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Why, Exactly, Are Ultraprocessed Foods So Hard to Resist? This Study Is Trying to Find Out.

Understanding why they’re so easy to overeat might be key to making them less harmful, some researchers say.

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By Alice Callahan

Photographs by Lexey Swall

Alice Callahan spent two days at the National Institutes of Health in Bethesda, Md., and interviewed more than a dozen researchers about ultraprocessed foods.

• Published July 30, 2024 Updated July 31, 2024

It was 9 a.m. on a Friday in March, and Ernest Jones III was hungry.

From a hospital bed at a research facility at the National Institutes of Health in Maryland, he surveyed his meal tray: Honey Nut Cheerios with fiber-enriched whole milk, a plastic-wrapped blueberry muffin and margarine.

Listen to this article with reporter commentary

“Simple, old school,” one of those “Saturday morning breakfasts from back in the day,” said Mr. Jones, 38, who is studying to become a pastor.

He was about halfway through his 28-day stay at the N.I.H., and Mr. Jones was one of 36 people participating in a nutrition trial that is expected to be completed in late 2025. For one month each, researchers will draw participants’ blood, track their body fat and weight, measure the calories they burn, and feed them three meticulously designed meals per day.

The subjects don’t know it, but their job is to help answer some of the most pressing questions in nutrition: Are ultraprocessed foods harmful to health? Are they a major driver of weight gain and obesity? And why is it so easy to eat so many of them?

If researchers can answer these questions, they say, perhaps there are ways to make ultraprocessed foods healthier.

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• Correspondence
• Published: 24 July 2024

Consensus on commitment and action to monitor healthy diets

• Lynnette M. Neufeld   ORCID: orcid.org/0000-0003-2652-9108 1 ,
• Edward A. Frongillo   ORCID: orcid.org/0000-0002-8265-9815 2 ,
• Jennifer C. Coates   ORCID: orcid.org/0000-0001-6510-3199 3 ,
• Victor M. Aguayo   ORCID: orcid.org/0000-0003-1825-4108 4 &
• Francesco Branca 5  

Nature Food volume  5 ,  pages 533–534 ( 2024 ) Cite this article

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Diets are not monitored towards global nutrition-related targets either, despite clear commitments to “ensure access by all people to safe, nutritious and sufficient food” explicit in Sustainable Development Goal (SDG) 2. Current SDG 2 indicators, which capture undernourishment (that is, insufficient dietary energy supply at a national level), food insecurity, and nutritional status of children and women, do little to provide insights into the population-level consumption of healthy diets.

For example, in 2017 and 2018, the prevalence of undernourishment estimates for Tajikistan and Nigeria were relatively similar (11.6% and 10.4%, respectively) (Table 1 ). However, minimum diet diversity for women (MDD-W), collected in the same years through the Demographic and Health Surveys, revealed that although 80% of women of reproductive age were reaching MDD-W in Tajikistan, only 56% of women achieved MDD-W in Nigeria. The corresponding prevalence of minimum dietary diversity for children (MDD-C) was 22.5% in Tajikistan in the same year and 31.1% in Nigeria (2021). That is, with the same national availability of dietary energy, women in Tajikistan were achieving far better dietary diversity than women in Nigeria. At the same time, less than a third of children in both countries were achieving MDD-C, but the prevalence was higher in Nigeria than in Tajikistan 4 .

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Acknowledgements

The HDMI core group acknowledges contributions to the initiative from S. Farley (the Rockefeller Foundation) and S. Sundberg (Bill & Melinda Gates Foundation). Funding for HDMI is gratefully acknowledged from the Rockefeller Foundation (organization, hosting and funding for the first group convening) and from the Bill & Melinda Gates Foundation (grant no. INV-063321) for ongoing efforts. The findings and conclusions contained within are those of the authors/contributors and do not necessarily reflect positions or policies of author’s or acknowledged individual’s affiliate organizations or funders.

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Lynnette M. Neufeld

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Edward A. Frongillo

Tufts University, Friedman School of Nutrition Science and Policy, Boston, MA, USA

Jennifer C. Coates

United Nations Children’s Fund (UNICEF), New York, NY, USA

Victor M. Aguayo

World Health Organization (WHO), Geneva, Switzerland

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Neufeld, L.M., Frongillo, E.A., Coates, J.C. et al. Consensus on commitment and action to monitor healthy diets. Nat Food 5 , 533–534 (2024). https://doi.org/10.1038/s43016-024-01016-8

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Your environment. your health., nutrition, health, and your environment, what is niehs doing, further reading, introduction.

What we eat is considered an environmental factor that influences health, in positive and negative ways. Healthy diets with an optimal balance of nutrients help people accomplish daily physical activities and mental processes. Within your diet, a deficiency or excess of certain nutrients can affect health.

The term diet refers to foods and beverages consumed over time in all settings, such as worksites, schools, restaurants, and the home. Diet also often means a specific nutritional plan or eating pattern.

Nutrition is the process of consuming, absorbing, and using nutrients from food that are necessary for growth, development, and maintenance of life.

What Are Nutrients?

Nutrients give your body energy and enable bodily functions. They are usually classified in two major groups:

• Macronutrients , in the form of protein, carbohydrate, or fat, primarily provide energy to your body. The different macronutrients serve different energy pathways and functions in the body. Energy from macronutrients in food is measured in units called calories.
• Micronutrients , known as vitamins and minerals, are required by the body in minute amounts. They protect and promote various bodily functions, including processing energy from macronutrients. Although critical to health, micronutrients do not supply energy.

What Should People Eat?

As reflected in the federal Dietary Guidelines for Americans , scientific evidence shows that healthful eating patterns can help people achieve and maintain well-being and reduce their chance of chronic disease. The guidelines also say that people can enjoy foods that meet their personal needs and cultural preferences while eating healthfully.

By translating science into succinct, food-based guidance, the guidelines are intended to help the U.S. population at large choose a better diet. Specific nutritional recommendations for individuals suffering from diet-related conditions are not provided.

The Dietary Guidelines for Americans are jointly developed and issued by the U.S. Department of Agriculture and the U.S. Department of Health and Human Services. Updated every five years, they are the cornerstone for many federal nutrition programs and policies.

Why Study Nutrition and Health?

More than half of U.S. adults – 129 million people – have one or more preventable chronic diseases, such as cardiovascular disease, high blood pressure, type 2 diabetes, and some cancers, which are often related to diet and physical inactivity.

Beyond health effects, nutrition-related diseases create strains on productivity, health care spending, health disparities, and military readiness . Addressing such issues requires understanding interrelated biological and social environmental determinants, and corresponding solutions.

As a scientific field, nutrition is integral to health promotion and disease prevention. Information from many disciplines, including anthropology, biology, biochemistry, economics, epidemiology, food science and technology, genetics, physiology, psychology, and sociology, are applied in nutritional studies. Scientists consider what people eat and drink, and take as dietary supplements, during different life stages and over time. They focus on interconnections to build evidence for public policy, health system, and environmental improvement strategies.

Nutrition Research at the National Institutes of Health

The Precision Medicine Initiative is a long-term research project at NIH. This initiative aims to understand how a person's genetics, environment, and lifestyle can determine the best approaches to prevent or treat disease.

As part of the Precision Medicine Initiative, NIH has a plan to accelerate nutrition research. While dietary guidelines and related public health approaches can help improve nutritional status across a population, researchers have growing appreciation for how different factors may affect people differently.

NIH nutrition research will help answer: what should I eat to stay healthy ?

The 2020 – 2030 Strategic Plan for NIH Nutrition Research focuses on how nutrition and dietary patterns affect all health conditions and emphasizes the importance of understanding variation among people. NIEHS assists with the coordination and implementation of this nutrition research plan.

With funding and support from NIEHS, scientists are looking at whether certain nutritional components may protect people’s health when they are exposed to harmful chemicals and other environmental hazards. Scientists are also studying whether environmental factors can worsen health conditions related to nutrition or dietary patterns.

Nutrition May Reduce Harmful Health Effects From Environmental Factors

The concept of reducing risk from harmful exposures tends to mean removing or decreasing exposure to environmental contaminants. But that form of prevention can be difficult to achieve. An alternative concept is to focus on nutrients with potential to be protective or reduce the risk of harmful health effects from environmental factors.

Researchers at the NIEHS-funded University of Kentucky Superfund Research Center have an innovative, long-running program that studies if and how nutrition can reduce the risk of harmful health effects from environmental pollutants. Their research is based on the premise that nutrition should be considered a necessary variable in the study of human diseases associated with exposure to environmental contaminants.

Based on years of study, there is evidence that certain aspects of nutrition are protective and should be integral in efforts to intervene or prevent toxic health effects of some environmental factors.

For example, the researchers uncovered how a person’s diet can protect against the harmful health effects of exposure to polychlorinated biphenyls (PCBs). Now banned from production, PCBs were once commonly used in making products such as heat transfer fluids and coolant in electric transformers. They discovered that certain nutrients, vitamin E and omega 3-fatty acids , can reduce cell damage from PCB exposure and that a type of fiber found in vegetables can potentially protect against cardiovascular problems related to PCB exposure. Conversely, they also found that dietary fat that is high in linoleic acid can worsen the cardiovascular effects of PCBs.

Other Findings From NIEHS-supported Research Include the Following:

ADHD – Researchers demonstrated that low vitamin D during pregnancy was related to an increased risk of attention deficit hyperactivity disorder (ADHD), a finding that could lead to new prevention measures.

Asthma – Asthma is a common childhood disease that disproportionately affects urban minority populations. Researchers discovered that vitamin D has a protective effect among children with asthma who live in urban environments with poor indoor air quality. In other words, obese children with blood levels low in vitamin D had worse asthma than children with higher vitamin D levels.

A diet deficient in antioxidants--micronutrients that help defend cells in the body--has been suggested as one reason for the asthma epidemic. The traditional Mediterranean diet typically includes foods rich in antioxidants such as vegetables, fruits, nuts, fish, and olive oil, with a low intake of meat. This diet pattern has been shown to be protective of asthma and allergic disease in multiple studies. A study funded by NIEHS found that following this type of diet reduced the chance of asthma development among children in Lima, Peru.

Autism Spectrum Disorder – Autism spectrum disorder (ASD) is a broad range of conditions that affect communication and behavior. Environmental factors and genetics are thought to contribute to ASD, which affects 1 in 36 children in the U.S.

While more research is needed on the potential role nutrition may play in the development of ASD, studies reveal promising findings.

• Taking a prenatal vitamin during early pregnancy was associated with a lower rate of ASD in a 2021 study. This finding indicates that prenatal vitamins or supplemental folic acid could be preventative for ASD.
• The younger siblings of children with ASD have a greater chance of developing the disorder due to shared genetics and similar environment. A NIEHS-funded researcher reported, in 2019, that when mothers of these children took prenatal vitamins with folic acid in the first month of pregnancy, the recurrence of autism was reduced by about half . Folic acid is the synthetic form of folate, also known as vitamin B-9, which is found in many foods, such as dark-green leafy vegetables, beans, peas, broccoli, and oranges.

Autoimmune Diseases – Lupus, an autoimmune disease, occurs when your body's immune system attacks your own tissues and organs, affecting many different body systems. Lupus can flare up when genetically predisposed people encounter certain environmental agents, such as air pollutants, pesticides, or other chemicals. A study funded by NIEHS found that dietary micronutrients could either improve or worsen lupus symptoms . Study results suggest that dietary modification, such as more vitamin B-12, zinc, and folic acid, might be a therapeutic approach warranting further investigation in lupus patients.

Other NIEHS-funded research indicates that adequate vitamin D levels may be important for preventing immune dysfunction in older people.

Brain Health – Consuming omega-3 fatty acids, found in fish and flaxseed oil, may protect against brain shrinkage in older women who live in areas with high levels of air pollution called fine particulate matter (PM2.5).

Women living in locations with higher PM2.5 had significantly less white matter in their brains, a sign of shrinkage. But in those locations, women with high blood levels of omega-3 fatty acids had white matter that appeared healthier.

Cancer – More than 20 years ago, NIEHS researchers demonstrated a gene-diet interaction in a study that found isothiocyanates, a compound in cruciferous vegetables (e.g., broccoli, cauliflower, and cabbage), was protective against lung cancer.

In-house researchers at NIEHS found that vitamin D supplementation may be useful in breast cancer prevention . The study looked a group of women with a higher risk of developing breast cancer. The women who had high blood levels of vitamin D and regularly took vitamin D supplements had lower rates of postmenopausal breast cancer over a 5-year follow-up period.

Cardiometabolic disorders – These conditions include cardiovascular problems, diabetes, and nonalcoholic fatty liver disease. Dietary fiber may protect against metabolic and fatty liver diseases related to perfluorooctoane sulfonate (PFOS) exposure, according to a NIEHS-funded study  in mice. Study results may be useful for designing intervention strategies to reduce disease risk in PFOS-exposed populations.

A NIEHS-funded study found that triclosan , an antimicrobial found in medical soaps and household products, accelerated development of fatty liver, fibrosis, and nonalcoholic fatty liver disease  in mice that ate a high-fat diet. Understanding the molecular mechanisms by which triclosan disrupts metabolism and the gut microbiome, while also stripping away liver cells’ natural protections, may provide a basis on which to develop therapies.

Obesity is a chronic health condition that increases the chance of developing cardiometabolic disorders. High lead levels during pregnancy were linked to child obesity in a large study, partially funded by NIEHS . Children born to women who have high blood lead levels are more likely be overweight or obese, compared to children whose mothers have low levels of lead in their blood. But women who take folic acid supplements during pregnancy may reduce the chance that their children are obese.

Inflammation – Many epidemiological studies provide evidence that cardiovascular diseases are linked to environmental pollution . NIEHS-funded researchers found that a mix of B vitamins (folic acid, B-6, and B-12) may protect DNA in immune cells from harmful effects of PM2.5 air pollution. They found that this pollution caused changes in DNA related to inflammation and metabolism, which may be tied to cardiovascular or respiratory conditions. According to the researchers, dietary supplementation with B vitamins almost completely prevented the changes to DNA that may lead to adverse health effects.

Reproductive Health – There is growing acceptance that nutrition may be related to fertility, and specifically the success of infertility treatment in women. NIEHS-funded research found that women consuming a “pro-fertility” diet that included supplemental folic acid, vitamin B12, vitamin D, low-pesticide fruits and vegetables, whole grains, seafood, dairy, and soy foods have a greater chance of live birth following assisted reproductive technologies.

The same researcher found folic acid could counter the adverse effects of air pollution on reproductive success in women using assisted reproductive technology. Air pollution can harm reproduction through a variety of biological mechanisms, including oxidative stress, endocrine disruption, DNA methylation, an altered immune response, and inflammation. Given exposure to traffic-related air pollution, pregnant women who took folic acid had a greater chance of their pregnancy resulting in a live birth .

Environmental Factors Affect Nutrition

Eating Fish – Eating fish can provide many health benefits, but consumers should be cautious. Some types of fish caught in certain areas are lower in mercury, PFAS, and other contaminants than other fish. Fish consumption advisories help people understand what fish are safe to eat, for whom, and in what quantities.

Researchers supported by NIEHS, for example, developed the Eat Fish, Choose Wisely guide for North Carolina residents, which includes a color-coded map for people to identify areas where they can catch fish that are safer to eat.

Fish consumption during pregnancy is a complex scientific topic. Other NIEHS-supported researchers created a framework for untangling questions about the risks and benefits of fish consumption. It could help produce clearer guidance on fish consumption for pregnant mothers .

A 2024 study found that people who frequently eat seafood may have an increased risk of exposure to PFAS, and this source of exposure may be underestimated. Among all types of seafood sampled in the study, the highest PFAS concentrations were found in shrimp and lobster. The New Hampshire-based researchers said that because PFAS are in many aspects of the environment, it is unclear where and how these chemicals enter the marine food chain. More research is needed.

Food Environments – A systematic review published in 2020, partially funded by NIEHS, suggests that the health of some children may be affected by food environments near schools . Researchers examined the presence of fast-food outlets, convenience stores, supermarkets, and grocery stores near schools along with measures of overweight/obesity by race/ethnicity, gender, grade, and income level.

This review found that when fast food outlets were located near schools, obesity rates were generally higher among children in all grade levels. Additional research is needed to better understand this finding, especially for children at higher risk of obesity, such as those from socio‐economically disadvantaged populations.

Food Packaging – PFAS are a group of more than 15,000 perfluoroalkyl and polyfluoroalkyl substances , a class of chemicals associated with harmful health effects, including liver damage, cancer, and impaired immunity . Due to wide-spread usage, PFAS are in the blood of nearly every American , according to the Centers for Disease Control and Prevention.

• Some PFAS have grease-repellent properties and were added to food packaging. A National Science Foundation study, in 2017, found PFAS coatings on 46% of food-wrap papers and 20% of paperboard containers collected from fast-food restaurants across the U.S. In a subsequent, related NIEHS-funded study, consumption of meals from fast food, and pizza and other restaurants, was generally associated with higher serum PFAS concentrations in people . In the same study, consumption of microwave popcorn was associated with significantly higher serum levels of certain PFAS chemicals. A 2024 study by the international Food Packaging Forum identified 68 PFAS in various food contact materials, including paper, plastic, and coated metal.
• In February 2024, FDA announced that grease-proofing materials containing certain PFAS are no longer being sold for use in food packaging in the U.S.

Food Safety – Food safety studies funded by NIEHS include contaminants in common foods. In particular, arsenic, a metal-like element that can harm many human organs, presents a global food contamination problem.

Researchers measured arsenic concentrations in several rice-based products. They found high levels of arsenic in brown rice syrup , a substitute for corn syrup in many foods including toddler formula. This discovery informed the Food and Drug Administration’s Inorganic Arsenic in Rice Cereals for Infants: Action Level Draft Guidance for Industry and other federal actions and reports.

The problem of contaminants in food led researchers funded by the Superfund Research Program to develop approaches for addressing soils used to grow crops. Some are working on phytoremediation approaches that are cost-effective and ecologically friendly. Phytoremediation is a process that uses fast-growing plants in engineered systems to degrade, extract, contain, or immobilize contaminants from soil or groundwater .

One team is testing a species of a non-food crop plant called oilseed to absorb and concentrate arsenic in its stems and leaves. Once harvested, these plants could be safely destroyed through incineration. Then, the plan is for farmers to plant food crops in the soil remediated from arsenic. This project is ongoing through 2025.

Food Gardening – The need for affordable, healthy foods has increased public interest in home, school, and community gardens. While urban gardens provide numerous benefits, soil contamination may be an issue. Some NIEHS-funded researchers have taken on safe urban gardening in their community engagement projects. Examples include:

• Producing videos about safely gardening in areas where soil may have contaminants.
• Testing soil for lead and other contaminants and raising awareness of children’s health risks associated with exposure.
• Reducing exposures of urban gardeners to soil contaminants by empowering communities to implement effective, community-based exposure mitigation strategies.
• Evaluating arsenic in vegetables commonly home grown and the potential risk from consumption.
• Transforming former brownfield sites into community gardens with safe soil .

Food Security – Diet is widely recognized as a key contributor to human gut microbiome composition and function. A healthy gut microbiome can help the immune system develop, protect against pathogens, and enable proper food digestion. Researchers found the gut microbiome of adults with food insecurity , a lack of access to healthy food, differed from those who were food secure. This study is significant because it focused on a social factor rather than dietary components.

Intramural Research

The following large projects, conducted in-house at NIEHS, have research components that concern dietary patterns or nutrition.

Agricultural Heath Study – More than 89,000 farmers and their spouses in Iowa and North Carolina have been involved in this study since 1993. The collaborative research effort involves investigators from NIEHS, National Cancer Institute, Environmental Protection Agency, and National Institute for Occupational Safety and Health. This research project includes a dietary survey. A list of published papers is organized by year.

The Sister Study – From 2003 to 2009, more than 50,000 women across the U.S. and Puerto Rico, who were 35-74 years old and whose sister had breast cancer, joined this landmark research effort to find causes of breast cancer. Because of their shared environment, genes, and experiences, studying sisters provides a way to identify risk factors for breast cancer, which may lead to prevention. Participants complete health updates each year, which include dietary surveys. A list of published papers is organized by year.

Infant Feeding & Early Development Puberty Study (IFED-2) – This research study is looking at what babies eat and how they grow, including hormonal changes, into adolescence. It will improve understanding of why some kids go through puberty earlier or later than others. The age when puberty starts may be linked to a person’s future health.

NIEHS Clinical Research Unit

CaREFREE Study: Calorie Restriction, Environment, and Fitness: Reproductive Effects Evaluation – Women who develop irregular menstrual cycles may find it difficult to become pregnant. Researchers want to learn more about functional hypothalamic amenorrhea, an improperly performing hypothalamus in the brain, and how it can cause a woman’s period to stop temporarily. Dietary patterns and exercise may affect this function and change menstrual cycles. The CaREFREE study will look at how these factors may affect some women.

Stories from the Environmental Factor (NIEHS Newsletter)

• Diet and Exposures in Pregnancy: Grantee Tackles Research, Messaging (September 2023)
• Chemicals Formed in Well-done Cooked Meats May Be Risk Factors for Parkinson’s (September 2023)
• Anticancer Effects of Dietary Methionine Depend on Immune Status (September 2023)
• Folate’s Protective Effects May Now Extend to PFAS (July 2023)
• Baking Industry Food Additive Raises Red Flag, Expert Says (June 2023)
• Eating Fish While Pregnant: Benefits Outweigh Harms (June 2023)
• High-Fiber Diet May Protect Against Exposure to PFOS (April 2023)
• Precision Nutrition Improves Health at Individual Level, Expert Says (February 2023)
• Path to Food Safety Requires Multidisciplinary Approach, Experts Say (January 2023)
• Autism Researcher Focuses on Maternal Diet, Prenatal Exposures (October 2022)
• Effects of Flame Retardants, Maternal Diet on Children Focus of Talks (September 2022)
• Links Between Nutrition, Exposures, and Autism Focus of NIEHS Event (July 2022)
• North Carolina Fish Forum Turns Research Collaboration Into Action (July 2022)
• Diet holds key to slowing biological aging, researchers say  (November 2021)
• Good Nutrition Can Help Counter Effects of Contaminants, Expert Says (September 2021)

Printable Fact Sheets

Fact sheets.

Arsenic and Your Health

Autoimmune Diseases and Your Environment

Drinking Water and Your Health

Environment and Health A to Z

NTP Botanical Dietary Supplements Program

• Campaign Promotes Eating Safer Fish (2022) – The “ Stop, Check, Enjoy! ” campaign helps fishers in southeastern North Carolina understand the risks of consuming certain fish from the Cape Fear River.
• Community-engaged Research Leads to Soil Cleanup (2022) - Emory University works with residents of Atlanta’s Westside community to test their urban gardening soil for lead. This effort led to awareness of health risks and the removal of lead-contaminated soil in neighborhoods.
• Botanical Safety (2021) – Cynthia Rider, Ph.D., a toxicologist at NIEHS, describes how certain botanical dietary supplements may affect health and how consumers can make informed decisions.

Additional Resources

• Dejunking Your Diet: The Drawbacks of Ultra-Processed Foods (February 2024) – This NIH News in Health story says eating too much ultra-processed foods may lead to weight gain and increase risk for certain diseases. Tips for healthier eating are also given.
• Foodborne Diseases and Nutrition (NIEHS) – Climate change may affect foodborne illness, nutrition, and food security, which can affect many populations.
• Healthy Food Environments – From the CDC, learn about supports for people in making healthier food choices.
• National Agricultural Library, Food and Nutrition Information Center – For health professionals, this entity provides access to trustworthy food and nutrition resources from both government and non-government sources.
• NIH Office of Nutrition Research – Information about nutrition-related research funding opportunities at NIH.
• Nutrition – Public health nutrition information from the CDC.
• USDA Food and Nutrition – This federal department works to increase food security and reduce hunger by providing children and low-income people better access to a healthful diet and nutrition education.

Related Health Topics

• Gene and Environment Interaction
• Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)
• Safe Water and Your Health

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EDITORIAL article

Editorial: ethical and sustainable food choice: drivers and health effects.

• 1 Independent Researcher, Messina, Italy
• 2 Center for Complementary Medicine, Department of Medicine II, Faculty of Medicine, Medical Center, University of Freiburg, Freiburg, Germany

Editorial on the Research Topic Ethical and sustainable food choice: drivers and health effects

Since the lack of fair and appropriate access to food is a global public health problem affecting many populations, a transition toward a more sustainable food system is urgently required ( 1 ). While in low-income countries food access is often limited due to disadvantageous socio-economic conditions, high-income countries are nowadays frequently characterized by an excess supply of low-quality, energy-dense foods. The use of highly processed foodstuffs and poor dietary habits favor the onset of non-communicable chronic diseases, which could be largely prevented by adopting a plant-based diet ( 2 , 3 ). At the same time, countries with a rapid urbanization trend are adopting an increasingly Westernized diet with a prevalence of meat-based food options which poses strong health risks and an ecological impact that is not sustainable ( 4 , 5 ).

If we consider social, economic, health, and environmental aspects, a global system that ensures fair and regular access to high quality foods must include a broad concept of sustainability that embraces all these aspects ( 6 , 7 ). In particular, the typical diet of high-income countries, based on a large use of foods of animal origin, requires greater resources starting from the use of agriculture intended for the production of feed for livestock, with a more expensive environmental cost and a greater impact from by-products such as greenhouse gases ( 8 ). Arguably, a transition toward a diet based mostly on plant foods can satisfy all social, health and environmental critical issues, guaranteeing sustainable agriculture and promoting more homogeneous access to food among low-income countries and industrialized ones ( 9 , 10 ).

In this context, the drivers and barriers to encourage the adoption of more sustainable food choices cannot be underestimated ( 11 ). Dietary modifications frequently involve resistance by individuals and a correct and sensitive communication of the possible advantages for the planet and human health could have favorable effects ( 12 ).

In the pilot study “ A multi-center prospective study of plant-based nutritional support in adult community-based patients at risk of disease-related malnutrition ,” Delsoglio et al. enrolled 24 adults at risk of malnutrition who required nutritional support. The study aimed to verify the acceptability of a vegan option of an oral nutritional supplement. Taking into account the increase in demand for plant-based options, the authors studied the acceptability of a particular formulation that could satisfy this type of request. Participants were followed for 28 days during which they received dietary advice and support. The results suggested excellent compliance and tolerance with maintenance of appetite. While the nutritional status of participants improved subsequent to a higher energy intake (mainly from protein), malnutrition risk decreased.

The impact of food choices on health and the environment was explored in the manuscript “ Identification of three dietary groups in French university students and their associations with nutritional quality and environmental impact ” Arrazat et al. , examined a representative sample of 582 French students. Based on data from a 125-item food frequency questionnaire, the three distinct dietary patterns emerged. While 20% of the participants adopted a diet with high health indices but a high impact on the environment through greenhouse gas emissions, the other participants were equally divided between a Westernized diet, characterized by a high environmental impact and low health indices, and a frugal diet with lower environmental impact and intermediate health indices. These results highlight that among some segments of the population, it may still be necessary to adopt a dietary style which combines health and environmental advantages. The social determinants that emerged from this study (economic availability, age, and cohabitation in the family of origin) could help in this task.

Consistently, Patel et al. in “ Testing the effect of descriptive dynamic social norm messages on meatless food purchases in Aotearoa New Zealand and UK university food outlets ” conducted 2 parallel week-long intervention studies (in New Zealand and the UK) to test the effectiveness of social norm messages to reduce the consumption of animal-based foods. However, messages displayed in university food outlets and via social media did not appear to be effective in changing meat and meatless food purchases. This suggests that modifying eating behavior is challenging, and complex mechanisms may be taken into account. An approach not limited to descriptive dynamic social norm interventions may be warranted. Customers at food outlets could be profoundly influenced by social aspects that stimulate the maintenance of meat-based eating behaviors while at the same time, they could ignore messages that discourage a choice that they may have already planned at that moment. However, it should be mentioned that awareness of the messages was low in both studies, as emerged from a survey conducted among a subgroup of customers.

Resistance to the transition to a plant-based diet often stems from a misinterpretation of the possible risks associated with adopting a vegetarian diet. This may apply in particular to bone health, which is controversially discussed ( 13 ). However, as highlighted by Galchenko et al. in the cross-sectional study entitled “ Bone mineral density parameters and related nutritional factors in vegans, lacto-ovo-vegetarians, and omnivores: a cross-sectional study ,” there appeared no difference in bone mineral density among three different dietary patterns. Forty-four omnivores, 38 lacto-ovo vegetarians, and 46 vegans from Russia consumed less vitamin D than recommended without significant differences among groups. Vegans showed higher levels of PTH than omnivores but still within the normal range. This suggests that it is not the dietary lifestyle itself that represents possible deficiencies but some nutrients deserve particular attention when planning a sustainable diet.

Among the foods that can guide the dietary transition toward greater sustainability, legumes and common beans emerge as promising options, according to the review “ Legumes and common beans in sustainable diets: nutritional quality, environmental benefits, spread and use in food preparations ,” Lisciani et al. showed that the environmental and health sustainability, cost-effectiveness and versatility of legumes and common beans in traditional recipes and second-generation foods could easily guarantee fair access to food in low-income countries while mitigating the food excesses of industrialized countries.

Overall, this Research Topic brings together contributions emphasizing the importance of providing plant-based alternatives that can satisfy the growing demand among the world population but at the same time the need to implement effective strategies for a more sustainable food transition.

Author contributions

GR: Writing – original draft. MS: Writing – review & editing.

The author(s) declare that no financial support was received for the research, authorship, and/or publication of this article.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher's note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

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5. Khara T, Riedy C, Ruby MB. “We have to keep it a secret”—the dynamics of front and backstage behaviours surrounding meat consumption in India. Appetite. (2020) 149:104615. doi: 10.1016/j.appet.2020.104615

6. Dixon KA, Michelsen MK, Carpenter CL. Modern diets and the health of our planet: an investigation into the environmental impacts of food choices. Nutrients. (2023) 15:692. doi: 10.3390/nu15030692

7. Carey CN, Paquette M, Sahye-Pudaruth S, Dadvar A, Dinh D, Khodabandehlou K, et al. The environmental sustainability of plant-based dietary patterns: a scoping review. J Nutr . 2023:S0022-316606589-6. doi: 10.1016/j.tjnut.2023.02.001

8. Food and Agriculture Organization of the United Nations. Tackling Climate Change through Livestock. A Global Assessment of Emissions and Mitigation Opportunities . Policy Support and Governance. (2023). Available online at: https://www.fao.org/policy-support/tools-and-publications/resources-details/en/c/1235389/ (accessed August 27, 2023).

9. EAT. EAT-Lancet Commission Summary Report (2024). Available online at: https://eatforum.org/eat-lancet-commission/eat-lancet-commission-summary-report/ (accessed June 25, 2024).

10. CORDIS European Commission. Growing Sustainable Agriculture Through Local Legumes . (2023). Available online at: https://cordis.europa.eu/article/id/434323-growing-sustainable-agriculture-through-local-legumes (accessed September 27, 2023).

11. Sanchez-Sabate R, Sabaté J. Consumer attitudes towards environmental concerns of meat consumption: a systematic review. Int J Environ Res Public Health. (2019) 16:1220. doi: 10.3390/ijerph16071220

12. Marteau TM. Towards environmentally sustainable human behaviour: targeting non-conscious and conscious processes for effective and acceptable policies. Philos Trans Royal Soc A Math Phys Eng Sci. (2017) 375:20160371. doi: 10.1098/rsta.2016.0371

13. Hsu E. Plant-based diets and bone health: sorting through the evidence. Curr Opin Endocrinol Diabetes Obes. (2020) 27:248–52. doi: 10.1097/MED.0000000000000552

Keywords: vegetarian, vegan, plant-based, flexitarian, climate change, environmental, ethical, sustainability

Citation: Rizzo G and Storz MA (2024) Editorial: Ethical and sustainable food choice: drivers and health effects. Front. Nutr. 11:1455664. doi: 10.3389/fnut.2024.1455664

Received: 27 June 2024; Accepted: 16 July 2024; Published: 25 July 2024.

Edited and reviewed by: Barbara Burlingame , Massey University, New Zealand

Copyright © 2024 Rizzo and Storz. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Gianluca Rizzo, drgianlucarizzo@gmail.com

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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Healthy diet

• A healthy diet helps to protect against malnutrition in all its forms, as well as noncommunicable diseases (NCDs), including diabetes, heart disease, stroke and cancer.
• Unhealthy diet and lack of physical activity are leading global risks to health.
• Healthy dietary practices start early in life – breastfeeding fosters healthy growth and improves cognitive development, and may have longer term health benefits such as reducing the risk of becoming overweight or obese and developing NCDs later in life.
• Energy intake (calories) should be in balance with energy expenditure. To avoid unhealthy weight gain, total fat should not exceed 30% of total energy intake (1, 2, 3). Intake of saturated fats should be less than 10% of total energy intake, and intake of trans-fats less than 1% of total energy intake, with a shift in fat consumption away from saturated fats and trans-fats to unsaturated fats (3), and towards the goal of eliminating industrially-produced trans-fats (4, 5, 6).
• Limiting intake of free sugars to less than 10% of total energy intake (2, 7) is part of a healthy diet. A further reduction to less than 5% of total energy intake is suggested for additional health benefits (7).
• Keeping salt intake to less than 5 g per day (equivalent to sodium intake of less than 2 g per day) helps to prevent hypertension, and reduces the risk of heart disease and stroke in the adult population (8).
• WHO Member States have agreed to reduce the global population’s intake of salt by 30% by 2025; they have also agreed to halt the rise in diabetes and obesity in adults and adolescents as well as in childhood overweight by 2025 (9, 10).

Consuming a healthy diet throughout the life-course helps to prevent malnutrition in all its forms as well as a range of noncommunicable diseases (NCDs) and conditions. However, increased production of processed foods, rapid urbanization and changing lifestyles have led to a shift in dietary patterns. People are now consuming more foods high in energy, fats, free sugars and salt/sodium, and many people do not eat enough fruit, vegetables and other dietary fibre such as whole grains.

The exact make-up of a diversified, balanced and healthy diet will vary depending on individual characteristics (e.g. age, gender, lifestyle and degree of physical activity), cultural context, locally available foods and dietary customs. However, the basic principles of what constitutes a healthy diet remain the same.

A healthy diet includes the following:

• Fruit, vegetables, legumes (e.g. lentils and beans), nuts and whole grains (e.g. unprocessed maize, millet, oats, wheat and brown rice).
• At least 400 g (i.e. five portions) of fruit and vegetables per day (2) , excluding potatoes, sweet potatoes, cassava and other starchy roots.
• Less than 10% of total energy intake from free sugars (2, 7) , which is equivalent to 50 g (or about 12 level teaspoons) for a person of healthy body weight consuming about 2000 calories per day, but ideally is less than 5% of total energy intake for additional health benefits (7) . Free sugars are all sugars added to foods or drinks by the manufacturer, cook or consumer, as well as sugars naturally present in honey, syrups, fruit juices and fruit juice concentrates.
• Less than 30% of total energy intake from fats (1, 2, 3) . Unsaturated fats (found in fish, avocado and nuts, and in sunflower, soybean, canola and olive oils) are preferable to saturated fats (found in fatty meat, butter, palm and coconut oil, cream, cheese, ghee and lard) and trans- fats of all kinds, including both industrially-produced trans- fats (found in baked and fried foods, and pre-packaged snacks and foods, such as frozen pizza, pies, cookies, biscuits, wafers, and cooking oils and spreads) and ruminant trans- fats (found in meat and dairy foods from ruminant animals, such as cows, sheep, goats and camels). It is suggested that the intake of saturated fats be reduced to less than 10% of total energy intake and trans- fats to less than 1% of total energy intake (5) . In particular, industrially-produced trans -fats are not part of a healthy diet and should be avoided (4, 6) .
• Less than 5  g of salt (equivalent to about one teaspoon) per day (8).  Salt should be iodized.

For infants and young children

In the first 2 years of a child’s life, optimal nutrition fosters healthy growth and improves cognitive development. It also reduces the risk of becoming overweight or obese and developing NCDs later in life.

Advice on a healthy diet for infants and children is similar to that for adults, but the following elements are also important:

• Infants should be breastfed exclusively during the first 6 months of life.
• Infants should be breastfed continuously until 2 years of age and beyond.
• From 6 months of age, breast milk should be complemented with a variety of adequate, safe and nutrient-dense foods. Salt and sugars should not be added to complementary foods.

Practical advice on maintaining a healthy diet

Fruit and vegetables.

Eating at least 400 g, or five portions, of fruit and vegetables per day reduces the risk of NCDs (2) and helps to ensure an adequate daily intake of dietary fibre.

Fruit and vegetable intake can be improved by:

• always including vegetables in meals;
• eating fresh fruit and raw vegetables as snacks;
• eating fresh fruit and vegetables that are in season; and
• eating a variety of fruit and vegetables.

Reducing the amount of total fat intake to less than 30% of total energy intake helps to prevent unhealthy weight gain in the adult population (1, 2, 3) . Also, the risk of developing NCDs is lowered by:

• reducing saturated fats to less than 10% of total energy intake;
• reducing trans -fats to less than 1% of total energy intake; and
• replacing both saturated fats and trans- fats with unsaturated fats (2, 3) – in particular, with polyunsaturated fats.

Fat intake, especially saturated fat and industrially-produced trans- fat intake, can be reduced by:

• steaming or boiling instead of frying when cooking;
• replacing butter, lard and ghee with oils rich in polyunsaturated fats, such as soybean, canola (rapeseed), corn, safflower and sunflower oils;
• eating reduced-fat dairy foods and lean meats, or trimming visible fat from meat; and
• limiting the consumption of baked and fried foods, and pre-packaged snacks and foods (e.g. doughnuts, cakes, pies, cookies, biscuits and wafers) that contain industrially-produced trans- fats.

Salt, sodium and potassium

Most people consume too much sodium through salt (corresponding to consuming an average of 9–12 g of salt per day) and not enough potassium (less than 3.5 g). High sodium intake and insufficient potassium intake contribute to high blood pressure, which in turn increases the risk of heart disease and stroke (8, 11) .

Reducing salt intake to the recommended level of less than 5 g per day could prevent 1.7 million deaths each year (12) .

People are often unaware of the amount of salt they consume. In many countries, most salt  comes from processed foods (e.g. ready meals; processed meats such as bacon, ham and salami; cheese; and salty snacks) or from foods consumed frequently in large amounts (e.g. bread). Salt is also added to foods during cooking (e.g. bouillon, stock cubes, soy sauce and fish sauce) or at the point of consumption (e.g. table salt).

Salt intake can be reduced by:

• limiting the amount of salt and high-sodium condiments (e.g. soy sauce, fish sauce and bouillon) when cooking and preparing foods;
• not having salt or high-sodium sauces on the table;
• limiting the consumption of salty snacks; and
• choosing products with lower sodium content.

Some food manufacturers are reformulating recipes to reduce the sodium content of their products, and people should be encouraged to check nutrition labels to see how much sodium is in a product before purchasing or consuming it.

Potassium can mitigate the negative effects of elevated sodium consumption on blood pressure. Intake of potassium can be increased by consuming fresh fruit and vegetables.

In both adults and children, the intake of free sugars should be reduced to less than 10% of total energy intake (2, 7) .  A reduction to less than 5% of total energy intake would provide additional health benefits (7) .

Consuming free sugars increases the risk of dental caries (tooth decay). Excess calories from foods and drinks high in free sugars also contribute to unhealthy weight gain, which can lead to overweight and obesity. Recent evidence also shows that free sugars influence blood pressure and serum lipids, and suggests that a reduction in free sugars intake reduces risk factors for cardiovascular diseases (13) .

Sugars intake can be reduced by:

• limiting the consumption of foods and drinks containing high amounts of sugars, such as sugary snacks, candies and sugar-sweetened beverages (i.e. all types of beverages containing free sugars – these include carbonated or non‐carbonated soft drinks, fruit or vegetable juices and drinks, liquid and powder concentrates, flavoured water, energy and sports drinks, ready‐to‐drink tea, ready‐to‐drink coffee and flavoured milk drinks); and
• eating fresh fruit and raw vegetables as snacks instead of sugary snacks.

How to promote healthy diets

Diet evolves over time, being influenced by many social and economic factors that interact in a complex manner to shape individual dietary patterns. These factors include income, food prices (which will affect the availability and affordability of healthy foods), individual preferences and beliefs, cultural traditions, and geographical and environmental aspects (including climate change). Therefore, promoting a healthy food environment – including food systems that promote a diversified, balanced and healthy diet – requires the involvement of multiple sectors and stakeholders, including government, and the public and private sectors.

Governments have a central role in creating a healthy food environment that enables people to adopt and maintain healthy dietary practices. Effective actions by policy-makers to create a healthy food environment include the following:

• Creating coherence in national policies and investment plans – including trade, food and agricultural policies – to promote a healthy diet and protect public health through:
• increasing incentives for producers and retailers to grow, use and sell fresh fruit and vegetables;
• reducing incentives for the food industry to continue or increase production of processed foods containing high levels of saturated fats, trans -fats, free sugars and salt/sodium;
• encouraging reformulation of food products to reduce the contents of saturated fats, trans- fats, free sugars and salt/sodium, with the goal of eliminating industrially-produced trans- fats;
• implementing the WHO recommendations on the marketing of foods and non-alcoholic beverages to children;
• establishing standards to foster healthy dietary practices through ensuring the availability of healthy, nutritious, safe and affordable foods in pre-schools, schools, other public institutions and the workplace;
• exploring regulatory and voluntary instruments (e.g. marketing regulations and nutrition labelling policies), and economic incentives or disincentives (e.g. taxation and subsidies) to promote a healthy diet; and
• encouraging transnational, national and local food services and catering outlets to improve the nutritional quality of their foods – ensuring the availability and affordability of healthy choices – and review portion sizes and pricing.
• Encouraging consumer demand for healthy foods and meals through:
• promoting consumer awareness of a healthy diet;
• developing school policies and programmes that encourage children to adopt and maintain a healthy diet;
• educating children, adolescents and adults about nutrition and healthy dietary practices;
• encouraging culinary skills, including in children through schools;
• supporting point-of-sale information, including through nutrition labelling that ensures accurate, standardized and comprehensible information on nutrient contents in foods (in line with the Codex Alimentarius Commission guidelines), with the addition of front-of-pack labelling to facilitate consumer understanding; and
• providing nutrition and dietary counselling at primary health-care facilities.
• Promoting appropriate infant and young child feeding practices through:
• implementing the International Code of Marketing of Breast-milk Substitutes and subsequent relevant World Health Assembly resolutions;
• implementing policies and practices to promote protection of working mothers; and
• promoting, protecting and supporting breastfeeding in health services and the community, including through the Baby-friendly Hospital Initiative.

WHO response

The “WHO Global Strategy on Diet, Physical Activity and Health” (14) was adopted in 2004 by the Health Assembly. The strategy called on governments, WHO, international partners, the private sector and civil society to take action at global, regional and local levels to support healthy diets and physical activity.

In 2010, the Health Assembly endorsed a set of recommendations on the marketing of foods and non-alcoholic beverages to children (15) . These recommendations guide countries in designing new policies and improving existing ones to reduce the impact on children of the marketing of foods and non-alcoholic beverages to children. WHO has also developed region-specific tools (such as regional nutrient profile models) that countries can use to implement the marketing recommendations.

In 2012, the Health Assembly adopted a “Comprehensive Implementation Plan on Maternal, Infant and Young Child Nutrition” and six global nutrition targets to be achieved by 2025, including the reduction of stunting, wasting and overweight in children, the improvement of breastfeeding, and the reduction of anaemia and low birthweight (9) .

In 2013, the Health Assembly agreed to nine global voluntary targets for the prevention and control of NCDs. These targets include a halt to the rise in diabetes and obesity, and a 30% relative reduction in the intake of salt by 2025. The “Global Action Plan for the Prevention and Control of Noncommunicable Diseases 2013–2020” (10) provides guidance and policy options for Member States, WHO and other United Nations agencies to achieve the targets.

With many countries now seeing a rapid rise in obesity among infants and children, in May 2014 WHO set up the Commission on Ending Childhood Obesity. In 2016, the Commission proposed a set of recommendations to successfully tackle childhood and adolescent obesity in different contexts around the world (16) .

In November 2014, WHO organized, jointly with the Food and Agriculture Organization of the United Nations (FAO), the Second International Conference on Nutrition (ICN2). ICN2 adopted the Rome Declaration on Nutrition (17), and the Framework for Action (18) which recommends a set of policy options and strategies to promote diversified, safe and healthy diets at all stages of life. WHO is helping countries to implement the commitments made at ICN2.

In May 2018, the Health Assembly approved the 13th General Programme of Work (GPW13), which will guide the work of WHO in 2019–2023 (19) . Reduction of salt/sodium intake and elimination of industrially-produced trans- fats from the food supply are identified in GPW13 as part of WHO’s priority actions to achieve the aims of ensuring healthy lives and promote well-being for all at all ages. To support Member States in taking necessary actions to eliminate industrially-produced trans- fats, WHO has developed a roadmap for countries (the REPLACE action package) to help accelerate actions (6) . 

(1) Hooper L, Abdelhamid A, Bunn D, Brown T, Summerbell CD, Skeaff CM. Effects of total fat intake on body weight. Cochrane Database Syst Rev. 2015; (8):CD011834.

(2) Diet, nutrition and the prevention of chronic diseases: report of a Joint WHO/FAO Expert Consultation. WHO Technical Report Series, No. 916. Geneva: World Health Organization; 2003.

(3) Fats and fatty acids in human nutrition: report of an expert consultation. FAO Food and Nutrition Paper 91. Rome: Food and Agriculture Organization of the United Nations; 2010.

(4) Nishida C, Uauy R. WHO scientific update on health consequences of trans fatty acids: introduction. Eur J Clin Nutr. 2009; 63 Suppl 2:S1–4.

(5) Guidelines: Saturated fatty acid and trans -fatty acid intake for adults and children. Geneva: World Health Organization; 2018 (Draft issued for public consultation in May 2018).

(6) REPLACE: An action package to eliminate industrially-produced trans -fatty acids. WHO/NMH/NHD/18.4. Geneva: World Health Organization; 2018.

(7) Guideline: Sugars intake for adults and children. Geneva: World Health Organization; 2015.

(8) Guideline: Sodium intake for adults and children. Geneva: World Health Organization; 2012.

(9) Comprehensive implementation plan on maternal, infant and young child nutrition. Geneva: World Health Organization; 2014.

(10) Global action plan for the prevention and control of NCDs 2013–2020. Geneva: World Health Organization; 2013.

(11) Guideline: Potassium intake for adults and children. Geneva: World Health Organization; 2012.

(12) Mozaffarian D, Fahimi S, Singh GM, Micha R, Khatibzadeh S, Engell RE et al. Global sodium consumption and death from cardiovascular causes. N Engl J Med. 2014; 371(7):624–34.

(13) Te Morenga LA, Howatson A, Jones RM, Mann J. Dietary sugars and cardiometabolic risk: systematic review and meta-analyses of randomized controlled trials of the effects on blood pressure and lipids. AJCN. 2014; 100(1): 65–79.

(14) Global strategy on diet, physical activity and health. Geneva: World Health Organization; 2004.

(15) Set of recommendations on the marketing of foods and non-alcoholic beverages to children. Geneva: World Health Organization; 2010.

(16) Report of the Commission on Ending Childhood Obesity. Geneva: World Health Organization; 2016.

(17) Rome Declaration on Nutrition. Second International Conference on Nutrition. Rome: Food and Agriculture Organization of the United Nations/World Health Organization; 2014.

(18) Framework for Action. Second International Conference on Nutrition. Rome: Food and Agriculture Organization of the United Nations/World Health Organization; 2014.

(19) Thirteenth general programme of work, 2019–2023. Geneva: World Health Organization; 2018.

• Preventing noncommunicable diseases
• Global nutrition targets 2025: policy brief series
• Global database on the Implementation of Food and Nutrition Action (GIFNA)
• Five keys to safer food
• 5 keys to a healthy diet
• International food standards (Codex Alimentarius)
• Comprehensive implementation plan on maternal, infant and young child nutrition
• WHO Recommendations on the marketing of foods and non-alcoholic beverages to children
• Global Action Plan for the Prevention and Control of NCDs
• Guideline: sodium intake for adults and children
• Guideline: potassium intake for adults and children
• Preparation and use of food-based dietary guidelines

The MORE WIC! Team

Johns Hopkins Bloomberg School of Public Health

Bloomberg School of Public Health faculty have been engaged in research to design, support and modernize the WIC Program since the beginning of the program. The prototype for the National WIC Program was designed and piloted at this School and adopted nationally by Congress in 1974.  Recent projects include a  systematic review of the impact of WIC participation on maternal and child outcomes and the  Hopkins Participant Research Innovation Laboratory (HPRIL) to evaluate innovations to increase child retention in WIC. The Johns Hopkins WIC Program has served Baltimore City for more than 35 years. 

Laura Caulfield, PhD

As the Principal Investigator (PI) of MORE WIC!, Laura is responsible for overall leadership and administration of the program. She is a professor in the Department of International Health's Center for Human Nutrition and has over 35 years of research experience in maternal and child nutrition in the US, Canada and Latin America. She has conducted research with WIC populations on nutrition, infant feeding, and breastfeeding promotion, and served on the 2002 NASEM committee evaluating dietary risk criteria for WIC. She was the co-PI of the USDA/FNS HPRIL project that supported local agencies in the implementation and evaluation of innovations to increase child retention in WIC.

Susan M Gross, PhD '96, MPH, RDN, LDN

Susan is a co-investigator on the MORE WIC! project. She is an Associate Practice Professor in the Department of Population, Family and Reproductive Health at the Johns Hopkins Bloomberg School of Public Health and is the director of Johns Hopkins WIC Program. She is a specialist in maternal and child nutrition, and has extensive experience with WIC implementation, evaluation methods, quality improvement research techniques, and providing technical assistance to state and local WIC agencies. She was a co-investigator for the HPRIL project where she provided technical assistance to sub-grantees on evaluation.

Elizabeth Kushman, MPH

Elizabeth is a Senior Research Associate at the Center for Indigenous Health, supporting implementation of the Family Spirit Home Visiting model nationally and internationally. Elizabeth has more than 25 years of experience developing and managing maternal, infant and early childhood programs, as well as contributing to tribal, state and national policy development efforts.  She has experience in program piloting and evaluation, and population-based surveillance projects using vital record, PRAMS and BRFS data. She completed a Master of Public Health at the University of Michigan.

Michelle Estradé, DrPH, RDN

Michelle is a Research Associate at the Johns Hopkins Bloomberg School of Public Health. She completed her doctorate in public health at the Bloomberg School in 2024, with a dissertation focused on tribally-administered WIC programs and Indigenous health equity. As the Project Manager for MORE WIC!, Michelle works closely with the Principal Investigator to coordinate project activities and serves as the main point of contact regarding overall administration of MORE WIC!

Caiti Roth-Eisenberg, MPA, MSSP

With over a decade of experience in the health and human services sector, Caiti works to increase access to public nutrition programs so that families have the resources they need to thrive. Much of her work has focused on breaking down silos between WIC, SNAP, and Medicaid through cross-program data matching, outreach, and streamlined enrollment, and she has co-authored a toolkit on this subject with the Center on Budget and Policy Priorities. In her role with MORE WIC!, Caiti leads technical assistance with participating State agencies to help them achieve their project goals. 

Jeneé Saffold, JD

Jeneé is a Pennsylvania licensed attorney, with over a decade of experience in legal research, policy development, and regulatory compliance. In her previous role at Benefits Data Trust Jeneé was a subject matter expert on benefits law and state benefit agency data sharing for targeted outreach to bridge enrollment gaps. She is passionate about exploring innovative ways policy can be used to improve benefits access. Jeneé holds a Bachelor of Science from Northwest Missouri State University and a Juris Doctor from Saint Louis University School of Law.

National WIC Association (NWA)

NWA is the nonprofit voice of the 12,000 public health nutrition service provider agencies and the over 6.3 million mothers, babies, and young children served by the Special Supplemental Nutrition Program for Women, Infants and Children (WIC). NWA provides education, guidance, and support to WIC staff; and drives innovation and advocacy to strengthen WIC as we work toward a nation of healthier families.

Georgia Machell, PhD

Georgia is originally from Leeds, England. After completing a PhD in Food Policy from City University of London, Georgia joined the National WIC Association in 2015 as the Research and Evaluation Manager. She is currently serving as President and CEO of NWA and has over 15 years working in policy-driven food access on the local and national levels in both the US and UK. In 2022 Georgia completed a certificate in Nonprofit Executive Leadership from the McCourt School of Public Policy at Georgetown University. She is passionate about connecting the dots between research, policy, programming, operations, and governance to advance mission-driven work. She is committed to ensuring all people have equitable access to nutritious food. Georgia lives in Washington DC with her husband, 6-year-old daughter, and their spaniel.

Chloe Dillaway, MSPH, RD, LDN

Chloe is a Registered Dietitian with over a decade of experience in public health research, programs, and community-based practice. She is responsible for managing the National WIC Association’s activities related to WIC program innovation and technological advancements to improve the participant experience. Prior to joining NWA, she worked at the Maryland WIC State Office on outreach strategy and partnerships with healthcare providers and community partners.  She also worked as a nutritionist at the Johns Hopkins WIC program in Baltimore where she provided high-risk nutrition counseling to participants. Chloe holds a Bachelor of Arts from Tufts University in International Relations, Community Health and Spanish, and a Master of Science in Public Health from Johns Hopkins Bloomberg School of Public Health.

USDA Food and Nutrition Service

The Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) provides healthy foods, breastfeeding support, health care and social services referrals, and nutrition information to income-eligible pregnant, breastfeeding, and non-breastfeeding postpartum women, and to infants and children up to age 5. USDA is investing in WIC to: 

• reach more eligible families
• keep families in WIC until they are no longer eligible
• encourage families to redeem more of their food benefits
• advance equity

Learn more about efforts to modernize WIC .

• Open access
• Published: 02 August 2024

Advances in single-cell transcriptomics in animal research

• Yunan Yan 1 ,
• Senlin Zhu 1 ,
• Minghui Jia 1 ,
• Xinyi Chen 1 ,
• Wenlingli Qi 1 ,
• Fengfei Gu 1 , 2 ,
• Teresa G. Valencak 1 , 3 ,
• Jian-Xin Liu 1 &
• Hui-Zeng Sun   ORCID: orcid.org/0000-0001-5380-6030 1 , 2  

Journal of Animal Science and Biotechnology volume  15 , Article number:  102 ( 2024 ) Cite this article

Metrics details

Understanding biological mechanisms is fundamental for improving animal production and health to meet the growing demand for high-quality protein. As an emerging biotechnology, single-cell transcriptomics has been gradually applied in diverse aspects of animal research, offering an effective method to study the gene expression of high-throughput single cells of different tissues/organs in animals. In an unprecedented manner, researchers have identified cell types/subtypes and their marker genes, inferred cellular fate trajectories, and revealed cell‒cell interactions in animals using single-cell transcriptomics. In this paper, we introduce the development of single-cell technology and review the processes, advancements, and applications of single-cell transcriptomics in animal research. We summarize recent efforts using single-cell transcriptomics to obtain a more profound understanding of animal nutrition and health, reproductive performance, genetics, and disease models in different livestock species. Moreover, the practical experience accumulated based on a large number of cases is highlighted to provide a reference for determining key factors (e.g., sample size, cell clustering, and cell type annotation) in single-cell transcriptomics analysis. We also discuss the limitations and outlook of single-cell transcriptomics in the current stage. This paper describes the comprehensive progress of single-cell transcriptomics in animal research, offering novel insights and sustainable advancements in agricultural productivity and animal health.

Introduction

Cells, the basic unit of life, vary widely in shape, size, and gene expression. It is vital to explore the different biological properties of individual cells in complex tissues to understand the process of life activities. The invention of flow cytometry at the end of the 1960s was a major breakthrough in both qualitative and quantitative measurements of cellular characteristics, as well as cell sorting [ 1 ]. It remains a widely applied strategy for single-cell analysis and isolation to date. In 1990, polymerase chain reaction was introduced to amplify DNA or RNA in individual cells, providing even more functional information [ 2 ], which further demonstrated that transcriptomic studies on individual cells were feasible. However, this method is limited by amplification bias and low throughput. The development of first-generation sequencing techniques made significant progress in molecular sequencing technology, but the costs remained high, and the sequencing throughput was low [ 3 , 4 ]. Next-generation sequencing technologies, such as “sequencing by synthesis” and accelerated parallel sequencing, have successfully overcome the above limitations, and RNA sequencing (RNA-Seq) is the best-known and most commonly used approach to date [ 5 ]. RNA-Seq involves total RNA extracted from organs, tissues, or a group of cells, obtaining average transcriptomic data while often masking specific information of individual cells in the population. To systematically study complex biological processes at higher resolution and reveal functional heterogeneity within tissues, researchers have developed a series of technologies, including multidimensional studies at the single-cell level. In 2009, Tang’s team developed the single-cell RNA sequencing (scRNA-Seq) method, enabling large-scale access to gene expression information from individual cells [ 6 ]. Since then, the use of scRNA-Seq has undergone rapid growth and evolution. In 2018, the journal “Science” ranked scRNA-Seq at the top of its list of the year’s most noteworthy technologies. Using scRNA-seq, international research projects, such as the Human Cell Atlas ( https://www.humancellatlas.org/ ), have been launched to identify all cell types involved in human development, health, and disease. Notably, a collaborative project consortium focusing on livestock, FarmGTEx ( http://farmgtex.org/ ), joined forces in the single-cell transcriptomic research of different livestock species by bringing together researchers from around the world to discover regulatory variants, molecular targets, and phenotype predictions at the single-cell level. Single-cell technologies are now emerging at multiple molecular levels, including genomics, transcriptomics, epigenomics, proteomics, and metabolomics, at continuously enhanced resolution, accuracy, and efficiency, setting the stage for the practical application of single-cell technologies.

Single-cell RNA sequencing is a technology that can be used to comprehensively reveal the gene expression profiles of cells by sequencing transcripts in individual cells one by one [ 7 ]. It is currently the most mature technology for high-throughput functional resolution at the single-cell level. As shown in Fig.  1 , the process begins with the dissociation of fresh tissue into a single-cell suspension, followed by the selection of different single-cell capture strategies depending on the cell numbers. Manual operations (e.g., limited dilution, laser cutting, micromanipulation) are generally chosen for small cell numbers, but microfluidic and microwell techniques are used when the cell throughput is on the order of tens of thousands [ 7 ]. After single-cell capture, cDNA is obtained through reverse transcription, amplified, and then sequenced. Downstream analysis can be conducted after completion of the single-cell sequencing run. The analysis process typically involves 3 stages: primary analysis (base detection), secondary analysis (multiple isolation, alignment, and genetic identification), and tertiary analysis (data visualization and interpretation) [ 8 ]. As scRNA-Seq involves a sufficient number of active cells from fresh samples, it is impossible to perform it efficiently from frozen or indigestible samples. The emergence of modern single-nucleus RNA sequencing has solved this problem by inserting an extraction procedure to extract the nuclei of single cells before isolating and labelling the nuclei, making it possible to detect nuclear gene expression at the single-cell level [ 9 , 10 ]. However, this method is currently not applicable for immune cells, and sequencing sensitivity may be low due to the low abundance of mRNA in the nuclei of some cells. Overall, single-cell transcriptomics has allowed us to fully decipher cell types/subtypes and functions in almost all species by constructing a reference catalogue of gene expression encompassing cells throughout the body. In addition, single-cell transcriptomic data can be visualized in multiple dimensions via bioinformatics analyses, such as differential enrichment and proposed time-series analyses. These strategies enable the reconstruction and simulation of biological system operations.

The workflow of single-cell/nucleus RNA sequencing

Livestock produces more than 15% of the world’s high-quality protein. The Food and Agriculture Organization of the United Nations predicts that by 2050, up to 50% of animal food will be required to feed 10 billion people. Rapidly emerging bioscience biotechnologies have assisted animal science experts in producing even more animal products with limited resources. However, when facing new challenges, such as studying the biological factors determining economic traits, product quality, and animal health, it is crucial to use high-throughput methods, especially single-cell transcriptomics, to better investigate cellular functions and interactions. Relevant research has already been conducted in animal studies worldwide using scRNA-Seq (see Additional file 1 for details). For example, identifying and annotating various cell types in livestock can reveal their specific functions and interactions, which is crucial for obtaining an even better understanding of the cellular composition, differentiation status, and intercellular regulatory networks in animal tissues and organs. This technology provides high-resolution information on gene expression in individual cells, facilitating the discovery and comparison of expression differences between cells and allowing for the identification of key genes related to economically important characteristics, nutrient metabolism, and disease resistance. In addition, scRNA-Seq can enable the discovery of new genes and regulatory elements, particularly those that are poorly expressed or cell-specific. Thus, our understanding of livestock animal genomes is enhanced, and a new approach to functional studies is provided. The transcriptomic changes in cells can be tracked at different time points via scRNA-Seq, revealing the dynamic processes of cell development, differentiation, and functional transformation. This information is important for understanding tissue growth, development, regeneration, and immune responses in livestock.

Our paper provides an overview of the use of scRNA-Seq in livestock research in recent years. It also offers insights and references on the single-cell data analysis process, which can serve to make scRNA-Seq a more robust tool for research on animal husbandry and breed optimization.

Applications of single-cell transcriptomics for livestock husbandry

Exploration of nutrient metabolism and immune responses.

The gastrointestinal tract (GIT) serves as a vital organ for nutrient absorption, and the mucosal immune system in animals largely affects production performance, animal welfare, and the safety of livestock products. Through single-cell sequencing of the livestock GIT, we will be able to investigate the composition and distinct metabolic patterns of various cell types, and ultimately, we may provide precise targets for nutritional manipulation and enhance nutrient absorption in these animals. Among the GIT in ruminants, the rumen holds undeniable significance for nutrient digestion and absorption, particularly for short-chain fatty acids (SCFAs), which are absorbed by the rumen epithelium and can meet 70%–80% of the body’s energy requirements [ 11 ]. However, the rumen epithelium is a complex structure consisting of four layers of cells of different types and functions. This complexity has hindered mechanistic explorations of rumen epithelial absorption and turnover of specific nutrients. Earlier scRNA-Seq work has shown that spiny cells of the rumen epithelium play a crucial role in SCFAs [ 12 ], but more detailed cell subtypes were not identified due to factors such as the lack of identified marker genes. The application of the newly developed rumen single-cell suspension preparation method for scRNA-Seq has given rise to even more comprehensive insights into rumen epithelial cell types. Wu et al. [ 13 ] integrated and expanded specific marker genes for bovine cell lineages based on previous studies; 20,728 rumen epithelial cells were clustered into 18 rumen epithelial cell types, and the specific metabolic characteristics of each cell subtype were characterized. The ability of different epithelial cells to absorb SCFAs was explored by analysing the expression of genes encoding transporter proteins and scoring the related functional pathways. The findings revealed that channel-gap-like (Cg-like) spinous cell regulated by IL-17 was the preferred subtype for SCFA absorption in dairy cows [ 13 ]. The microbiota is essential for nutrient absorption in the GIT, and further joint mining of rumen metagenomic data characterized the interactions between Cg-like cells and fibre-degrading bacteria via structural domains of the secreted proteins (Fig.  2 ) [ 14 ]. Unfortunately, the study did not address ruminal nutrient uptake during different developmental stages. Studies on intestinal nutrient absorption in monogastric animals based on single-cell transcriptomics have primarily concentrated on cross-species comparisons of distinct cell types and functional analyses. Specifically, studies have examined significant interspecies differences and regional characteristics in hormone-secreting enteroendocrine cell [ 15 , 16 ]. For example, there is a gradual decrease in the number of these cells after the birth of piglets [ 17 ].

Functional mechanism of rumen short-chain fatty acids uptake

The immune system is vital for animal health and plays a pivotal role in defending against external hazards by maintaining physiological equilibrium. The application of scRNA-Seq for investigating livestock immunity has generated valuable insights. The advent of scRNA-Seq has contributed to an in-depth understanding of functional heterogeneity, molecular regulatory mechanisms, and infection responses among cellular subsets within central immune organs (e.g., the bursa and thymus) and peripheral immune organs (e.g., Pyle’s collecting lymph node) [ 18 , 19 , 20 ]. However, investigations on the bone marrow of domestic animals remain a major issue. Single-cell transcriptional profiling of various immune cells, such as peripheral blood monocytes and lymphocytes of domestic animals, underlines the homology and species specificity of immune gene expression, providing a molecular basis for understanding the immune response process in livestock [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ]. For example, single-cell transcriptomic data of peripheral blood mononuclear cells (PBMCs) following disease in domestic animals have been used to identify pathogenic immune cell subpopulations and transcriptional modules driving pathogenesis [ 32 ]. This approach has helped with identifying subpopulations and molecular markers of PBMCs in chickens infected with avian influenza and avian leukemia virus [ 33 , 34 , 35 ], unravelling key signalling factors associated with lipopolysaccharide-induced glycolipid metabolism abnormalities in cattle [ 22 ], and uncovering cell types and genes linked to periparturient immunosuppression in dairy cows [ 36 ]. In recent years, single-cell sequencing research has shifted towards porcine immune cells during piglet weaning stress, weaning diarrhoea, and intestinal inflammation, as it enables the tracking of immune cell heterogeneity during pathogenic microbial infections and host responses during diseases. For example, scRNA-Seq analysis revealed that tumor necrosis factor-α secreted by different immune cells could contribute to disease, as observed in studies investigating African swine fever and porcine intestinal inflammation [ 37 , 38 ]. These observations have opened new avenues for the development of novel vaccines and targeted therapies. In summary, scRNA-Seq studies allow for the precise identification and analysis of cell types and their interactions involved in the immune processes of domestic animals. They also allow for the examination of regulated genes, signalling pathways, transcription factors, and immune cell subpopulations with potential pathogenic functions. Current studies primarily focus on exploring immune mechanisms, however the potential of scRNA-Seq could be harnessed to evaluate the efficacy and response to immunotherapy. This involves concentrating on T cells, which are important players in the immune response and play key roles in animal health.

Investigation of cell factors for animal reproductive performance

The level of reproductive performance in livestock, which can directly affect productivity, depends on the ability to produce high-quality male and female gametes. The use of scRNA-Seq combined with proposed time-series analysis has allowed for the careful investigation of the dynamic mapping of cell fate transitions and gene expression changes during spermatogenesis in dairy goats, sheep, yaks, and premature piglets [ 39 , 40 , 41 , 42 , 43 , 44 , 45 ]. Through comprehensive analyses, researchers have identified specific marker genes and key signalling pathways related to germ cells within the testes of farm animals. Furthermore, studies have explored the homology and differences in male germ lines across different species, expanding our understanding of testicular development and spermatogenesis [ 40 , 46 , 47 ]. It has become evident that spermatogenesis relies on an ecological niche composed of testicular somatic cells. Consequently, studies have increasingly focused even more on single-cell sequencing analyses of these cells over the past few decades. However, due to variations in study samples and resolution, there are significant knowledge gaps related to the classification of testicular somatic cells, necessitating further investigation [ 40 , 42 , 43 , 44 , 46 ]. The growth and development of ovarian follicles are primarily regulated by granulosa cells. Through single-cell transcriptomics, the heterogeneity and differentiation pathways of follicular cells and granulosa cells in the ovaries of livestock animals have been characterized [ 48 , 49 , 50 , 51 , 52 ]. However, intercellular interactions within the ovary remain poorly understood. Recent studies in yaks, goats, and domesticated pigs have attempted to fill this gap [ 53 , 54 , 55 , 56 ]. For instance, Chen et al. discovered that porcine ovarian mural granulosa cells primarily engage in intercellular communication with cells of the same type, whereas ovarian theca granulosa cells predominantly emit signalling cues to different cell types [ 53 ]. Nevertheless, these studies are based on relatively small sample sizes, and more in-depth work is needed to corroborate their findings. High-precision mapping of germ cell genesis in livestock animals has enabled researchers to conduct in-depth studies on the screening, diagnosis, and treatment of reproduction-related disorders, such as sperm damage, abnormal oocyte development, and male infertility, in the progeny of interspecifically crossbred individuals [ 57 , 58 , 59 ]. The regulatory characteristics and interspecific differences of various types of cells in the gonads of livestock animals obtained at specific time points represent another research focus that can be assessed by single-cell transcriptomics [ 60 , 61 , 62 ]. To date, continuous developmental differentiation in livestock gonads is poorly understood. Only the gonadal differentiation of the chicken embryo has been analysed, and the discovery that the supporting cells during gonadal differentiation in the chicken embryo are derived from mesenchymal stem cells, in contrast to other vertebrates, has revolutionized our previous understanding of gonadal cell types [ 63 ]. Notably, noncoding RNAs significantly affect the regulation of germ cell proliferation and differentiation in livestock [ 40 , 64 ]. However, capturing these noncoding RNAs remains challenging, necessitating advancements in the application of this technology to enhance our understanding of livestock reproductive performance [ 65 ].

Single-cell transcriptomics has also been widely accepted as an efficient tool for investigating cell fate and transcriptional regulation during embryonic development. Studies employing scRNA-Seq have examined embryos at various life stages in livestock, such as cattle, pigs, chickens, sheep, and rabbits, thus making dynamic transcriptional profiles and cellular differentiation trajectories accessible within each germ layer of early-stage embryos [ 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 ]. For example, these analyses have uncovered species-specific features of early embryonic development (E5-E13) in pigs, revealing the differentiation of bovine trophoblast mononuclear cells into binucleated cells and the changes in differential gene expression and associated signalling pathways from the 8-cell to the mulberry embryo stage in sheep [ 67 , 68 , 71 ]. By leveraging scRNA-Seq, researchers can also analyse embryos with developmental abnormalities or those transferred from in vitro cultures. These investigations contribute to identifying potential causes of developmental abnormalities, offering valuable guidance for improving reproductive techniques such as in vitro fertilization and embryo transfer. It has been observed that incomplete activation of certain metabolic pathways leads to metabolic abnormalities. Epigenetic modification may be responsible for the significant effects on subsequent pregnancy and calving rates in females, and comparing the developmental transcriptional profiles of embryos transferred in vitro from different states [ 75 ] may provide new ideas for the treatment of embryonic developmental abnormalities.

Elucidation of genetics and developmental biology in livestock

Throughout the ontogeny of an organism, the transcriptome of certain cells undergoes substantial transformation. scRNA-Seq represents a novel approach for elucidating the dynamic patterns of gene expression during livestock genetic development and for revealing the regulatory networks governing developmental and evolutionary processes. The ultimate goal is to depict the trajectory of cellular fate transformations. Developmental mapping has been performed on the nervous systems and skeletal limbs of monogastric animals [ 74 , 76 , 77 , 78 ] while focusing on the nodes and key cell types involved in the developmental differentiation of organs or tissues. It is worth mentioning that aided by single-cell transcriptomics of embryonic limbs in poultry, studies have pinpointed pivotal regulators and signalling pathways driving limb differentiation formation along with their regionalization for the first time [ 79 , 80 ]. Among ruminants, rumen development has received significant attention. Scientists have constructed a comprehensive developmental landscape of thirteen metabolic tissues in ruminants [ 81 , 82 ], which encompasses a holistic comparison of heterogeneity within rumen epithelial cell types, cell functions and interacting microbiota between calves and adults. These findings suggested that calf epithelial progenitor cells exhibit greater differentiation potential and display greater activity in cell proliferation, differentiation, and innate immune responses [ 81 , 82 ]. Conversely, adult bovine cells show prominence in immune cells and have increased activity during antioxidant, adaptive immune, and fatty acid metabolism processes [ 81 , 82 ]. Similarly, studies have shown that the keratinization process during rumen epithelial cell development is associated with the cessation of keratinocyte differentiation at specific stages [ 12 , 83 ]. Previous studies have successfully identified key genes associated with rumen growth and development by scRNA-Seq of the rumen epithelium [ 84 , 85 ]. Overall, scRNA-Seq is assisting in the construction of a developmental evolutionary tree of livestock from the embryo to the mature individual. In single-cell transcriptional studies on animal genetic development, previously unidentified cell types are discovered, such as a specific class of endothelial cell clusters found in yak lungs, were revealed as potential factors in plateau acclimatization, and it was shown that calf-specific STOML3 +  cells have the potential to maintain the internal environment of the liver [ 82 , 86 ]. In addition, the exploration of unexpected functionalities harboured by common cell types has become possible, e.g., luminal epithelial cells could be involved in both lactation and immune responses [ 13 ]. It is worth mentioning that whole-body single-cell atlases have been generated for several mammalian species [ 87 , 88 , 89 , 90 , 91 ], with those in humans and mice covering the entirety of life stages [ 92 ]. However, to date, comprehensive whole-body single-cell atlases are still lacking for livestock animals.

The comparison of single-cell transcriptomic data from high- and low-productivity livestock has become an approach to identify genes and key cell types related to economic traits and has led to the selection and breeding of highly productive livestock breeds. Taking meat production traits as an example, the quantity and quality of meat production largely depend on the development of skeletal muscle. Analyses of the single-cell transcriptomics of skeletal muscle from fat and lean pigs could effectively identify key genes for adipocyte differentiation and epigenetic modifications [ 93 , 94 , 95 ]. By analysing the developmental trajectories of myogenic progenitor cells, it was observed that the skeletal muscles of lean livestock were more closely related to myogenic progenitor cells and more responsible for muscle development than the skeletal muscles of fat pigs, suggesting that mechanistic explorations of myogenesis can lead to the study of differences in genealogical cell differentiation [ 93 , 96 ]. The identification of specific liver cell clusters between laying and non-egg-laying populations in egg-laying birds may also provide new insights for improving egg production in the future [ 97 ]. More information can also be acquired from single-cell transcriptomic studies of niche economic traits such as fleece- and silk-producing traits. The former is limited by the asynchronous development of the wool bursa [ 98 ], and the latter is limited by the understudied organ of the silk gland; neither the wool bursa nor silk glands have been accurately analysed previously for specific cell types. The emergence of scRNA-Seq has enabled in-depth knowledge of the distribution of the composition of each cell type and the trajectories of key cells during the different developmental periods of the wool bursa and silk glands [ 99 , 100 , 101 , 102 ]. Additionally, new marker genes involved in the synthesis of velvet and silk proteins have been identified [ 100 ], which can improve the quality of cashmere and silk. For instance, the ACTA2 , COL1A1 , and CLCL6 genes may regulate cashmere fineness [ 103 ]. Although single-cell transcriptomic analyses have shown promise for improving genetic breeding, current research results are difficult to apply in animal production or have limited impact. Future research concentrating on diseases that are commonly associated with production should follow. For example, particular cell subpopulations associated with mastitis in dairy cows can be identified.

Emergence of disease models

The utilization of scRNA-Seq in model animals is highly important, especially in pigs, an animal commonly used as a medical/disease model [ 104 , 105 , 106 ]. By employing scRNA-Seq, researchers have gained profound insights into the composition of organelle types between pigs and men, thereby revealing the heterogeneity and conservatism of gene expression and regulatory mechanisms within the biological processes of interest and promoting in-depth biomedical research and widespread use of the domestic pig as an animal model. Previous studies have focused on individual tissues or organs (e.g., immune cells [ 15 , 18 , 23 , 24 , 27 , 60 ], lungs [ 107 ], liver, embryos [ 108 ], the reproductive system [ 46 , 47 , 109 ], and the digestive tract [ 16 , 110 ]) in pigs. These studies utilized cross-species analyses to identify conserved or specific gene modules in tissues or screened for cellular subpopulations and risk genes associated with disease. Moreover, they have revealed gene–trait associations through modelling or induction. Pig lung tissue data were characterized for both similarities and differences in cellular communication and expression patterns of respiratory virus receptors in each cell type of the lung compared with human lung tissue data [ 107 ]. A comprehensive porcine brain atlas has facilitated the identification of cell types and risk genes linked to eight neurological disorders, e.g., attention deficiency [ 111 ]. Data from the pancreas have suggested that TXNIP , a stress gene in acinar cells, could become a potential target for the treatment of diabetes [ 112 ]. The investigation of the gallbladder in neonatal piglets has shed light on the mechanisms of cystic fibrosis-related hepatobiliary disease [ 113 ]. For the first time, a pioneering study constructed a porcine single-cell atlas database that comprehensively describes the heterogeneity of cells among 20 tissues/organs in pigs [ 114 ], providing a global view of tissue differences between domestic pigs and humans. Rather than focusing on specific cell clusters, Wang et al. [ 114 ] emphasized distinct functions and typical markers of endothelial cells commonly involved in different tissues and suggested that the endothelium may interact with cells through the VEGF, PDGF, TGF-β, and BMP pathways. Microglia have also been noted to be highly conserved across species during evolution [ 114 ], strongly supporting the view of pigs as an invaluable data resource for research on human diseases. In the context of xenotransplantation, pigs are considered the most suitable donors for human organ transplantation. However, the occurrence of rejection has restricted the application of this technique [ 115 ]. The expression patterns of ten genes associated with human immunobiological incompatibility and dysregulation of coagulation have been obtained across different cell types in pigs [ 107 ]. This discovery holds the potential to enhance the immunocompatibility of porcine xenotransplantation in the future through targeted genetic engineering, thereby improving survival after organ transplantation [ 116 ]. However, is important to note that the current study does not adequately address the influence of physiological states and manipulation on the samples. These factors may affect the results by leading to differing numbers of captured cells and altered cell typing. Future research should address this crucial aspect.

In addition to pigs, chickens and rabbits serve as valuable disease models for constructing single-cell reference maps. Differential cellular components can be identified by comparing “disease maps” with “normal maps”, which may in turn predict molecular disease mechanisms. For example, rabbits have been used to study mammalian cardiac contraction, proto-gut embryonic development, proliferative vitreoretinopathy, and hyperlipidaemia-induced spongiosis [ 72 , 117 , 118 , 119 ]. Similarly, chickens have proven valuable for investigating retinal development, hearing damage, and the mechanism underlying melatonin-related weight loss [ 120 , 121 , 122 ]. Among wild animals, antlers, a unique mammalian appendage capable of complete natural regeneration, have been demonstrated to grow similarly to long bones in humans. Leveraging the potential of scRNA-Seq, scientists have revealed key cell types and differentiation trajectories involved in antler regeneration [ 123 , 124 , 125 ], opening new avenues for exploring mammalian organ regeneration and organ damage repair. Future research should address the current limitations in genome annotations for reindeer [ 123 , 124 , 125 ].

Experience in single-cell transcriptomic data analysis

The optimal sample size for single-cell transcriptomic research.

Increases in sample size and sequencing depth could result in the discovery of new and rare cell types, encompassing both previously unrecognized entities and those present in tissues where they have not been detected before [ 126 ]. For instance, among 42,182 cells from three forestomach samples, T helper 17 and epithelial stem and progenitor cells were first identified in dairy cows [ 13 ]. A total of 29,231 individual cells were obtained from three samples of porcine adipose tissue, from which subtypes of cells transformed from endothelial to mesenchymal cells were distinguished [ 114 ]. Compared to studies in livestock, there are more instances of new cell type identification in humans and model organisms, such as a new specialized uroepithelial cell type discovered among 25,307 cells across three bladder samples in humans and mice [ 127 ] and four clusters of nonsensory epithelial cells of the ampulla identified from four stages of mouse crista ampulla samples [ 128 ]. Based on the aforementioned examples of novel cell discoveries, it is evident that employing three or more biological replicates and analysing over 20,000 cells significantly enhances the likelihood of uncovering new cell types. Considering the spatial positioning of tissue sampling and individual differences in cell dissociation, a larger number of biological samples further provides advantages in elucidating the comprehensive distribution of cell types. However, due to the high cost of reagents and sequencing (a total of 10–15 K RMB per sample), excessive sampling may cause more significant input and divert focus from validation experiments. As an illustration, in cell atlas studies, larger biological sample numbers are preferable for identifying cell types at higher resolution [ 21 , 44 , 102 ]. However, if the focus is solely on identifying which cell type is responsive to an experimental treatment, one biological replicate may be effective, as that one cell type typically consists of more than 20 cells/transcriptomes [ 129 , 130 ]. In addition, time-series designs generally involve fewer biological replicates than two-group comparisons [ 36 , 129 ].

With the development of single-cell sequencing technologies, an eight-channel microfluidic system that can capture up to 10,000 cells per channel has been developed, allowing for simultaneous detection of sample cell counts ranging from 50,000 to 800,000 cells in a single run [ 131 ], making a single sample cover a large number of cell/transcriptomic replicates. Bioinformatics tools allow us to enhance and refine the power of single-cell data analysis through the interpretation of transcriptome data. Deconvolution algorithms are now being employed to dissect bulk transcriptomic data to the single-cell level [ 132 ], increasing the statistical power of bulk transcriptomics in single-cell experiments. In addition to deconvolution algorithms, a framework for integrating single-cell RNA sequencing, epigenomic SNP-to-gene maps and genome-wide data enables the identification of target cell types based on the strong statistical power of GWAS data. Currently, emerging large-scale single-cell pre-trained models with tens of millions of cells, such as scGPT, can empower the tasks of our small datasets, including cell classification, network inference, and transcription factor perturbation analysis [ 133 ]. Taken together, researchers need to determine the amount of biological replication that is sufficient to capture biological variability and provide statistically significant results while considering the cost of experiments and the complexity of data analysis. Bulk sequence data and large-scale pre-trained models could be used to enhance the statistical power of single cells.

The number of cell clusters that optimally match the real situation

In brief, the number of cell types is determined by clustering algorithms; specifically, after obtaining single-cell datasets, the cells can be categorized into 2–5 major clusters based on automatic annotation and positional variance in the dimensionality reduction results. With major biological classifications, multiple higher resolutions could be used to identify the more specific cell types corresponding to the basic biological knowledge of a given tissue (Fig.  3 ). As an example, the large intestine comprises diverse epithelial cell types arranged in distinct configurations. Absorptive enterocytes predominate, lining the villi and crypts and specializing in the uptake of water, electrolytes, and nutrients from the luminal contents [ 134 ]. Goblet cells interspersed throughout secrete protective mucus, creating a mucosal barrier against pathogens and toxins [ 135 ]. Enteroendocrine cells release hormones to regulate digestive functions, while Paneth cells, predominantly found in the small intestine but also present in smaller numbers in the large intestine, contribute to innate immunity through the secretion of antimicrobial peptides [ 136 , 137 ]. Mesenchymal cells, immune cells, endothelial cells and neural cells are present in the large intestine. However, the epithelium of the intestine is usually composed of a single layer of columnar epithelial cells, such as those with 1 or 2 clusters, and some cuboidal cells, such as goblet cells, with 2 or 3 clusters [ 21 ]. Different resolution values should be tested to provide the finest demonstration of the known cell types within each tissue. Furthermore, based on the objectives and experimental design, the resolution and number of cell clusters may vary while maintaining biological features. A greater number of clusters is essential for key subcluster identification. For instance, specific macrophage and conventional dendritic cell subsets were identified as key mediators of cellular cross-talk in the colon tumour microenvironment from 54,285 cells divided into 40 clusters [ 138 ].

A summary of the common cell types identified in the gastrointestinal tract of livestock

Moreover, clustering algorithms should also be essential for generating the number of cell clusters. First, suitable algorithms should be chosen based on the cell numbers. The K-nearest neighbours algorithm is typically applied to datasets with small cell numbers, with the number of clusters predetermined before clustering. Moreover, the Louvain and Leiden algorithms are normally used for single-cell datasets with more than 100,000 cells, with the number of clusters determined by the resolution set by the analyser [ 139 , 140 ]. The number of clusters can be determined by intra- and intercluster similarity, community detection, eigenvector-based metrics, and stability [ 141 ]. However, these four predominant clustering methods lack systematic evaluation strategies for estimating the number of cell types. Therefore, stability-based approaches for estimating the number of cell types, such as scCCESS, have been proposed [ 141 ], enabling the estimation of the number of cell clusters without the need for researcher observation. Some bioinformatic visualization tools also help us estimate the number of clusters. The Clustree algorithm [ 142 ] employs a bottom-up hierarchical clustering approach for cluster information at different resolutions, which facilitates our selection of a suitable resolution by incorporating biological insights.

A well-formulated strategy for cell type identification

The identification of cell types is a fundamental and essential step in the analysis of single-cell transcriptome data and is accompanied by dimension reduction and clustering [ 143 ]. Generally, the number of cell types and the annotation results should be consistent with the corresponding physiological characteristics.

The common cell types identified in the GIT of livestock are summarized in Fig.  3 . The clusters can be classified into five main cell groups: epithelial cells, endothelial cells, stem cells, immune cells and others. We noticed that the number of clusters for immune cell types in the forestomach is generally lower than that in the intestine, while fibroblasts and muscle cells were more diverse. In the intestine, specifically in the small intestine, B cells and macrophages are more abundant. The cluster numbers correspond to substantial peristalsis and mechanical wear in the foregut, as well as the clear ability of the small intestine to eliminate exogenous invading microorganisms [ 144 ]. Collectively, these cells form a complex biological system responsible for digestion, nutrient absorption, protection against pathogens, and tissue repair and regeneration. Based on the previous cell group summary, we propose three approaches that are beneficial for identifying cell types: (1) collecting biological background information in a given situation; (2) referencing standard cell type names and databases; and (3) assisting in cell type identification with the help of bioinformatic software. It is necessary to summarize basic knowledge in the process of annotating cell types, including biological knowledge and standards/universal naming rules. Regarding how many types of cells should be classified, an effective method is to summarize the physiological characteristics of animal tissues through the accumulation of relevant experimental data and scientific research results [ 143 ]. For example, according to basic knowledge, the cell types present in the epithelial tissue of the rumen of dairy cows consist of four layers of epithelial cells (basal, spiny, granular, and stratum corneum; stratum corneum cells are dead cells and will not be captured), immune cells residing in the tissue, endothelial cells in the connective tissue, smooth muscle cells, and fibroblasts [ 13 ]. Therefore, the presence of these cell types can be used as a reference when determining whether the number of cell types is accurate and whether the current clustering parameters should be adjusted. In animal science research, genes related to animal production or health traits may have corresponding biological significance to cell type. For example, Wu et al. [ 13 ] found a new subcluster of rumen epithelial cells called channel gap-like spinous cells in dairy cows via an in-depth analysis of solute carrier gene expression. Additionally, Wang et al. identified EndMT cells as critical for endothelial-to-mesenchymal transition (EndMT) based on gene expression in stromal and endothelial cells [ 114 ].

To make the cell type identification results more biologically meaningful, the integration of public databases and bioinformatics analysis software should be considered. Public databases of single-cell transcriptome data, such as the Human Cell Atlas, incorporate marker genes for cell type identification and standard or universal cell type nomenclature rules [ 145 ]. In animal science research, the cattle cell atlas constructed by Wu et al. [ 82 ] and the pig cell atlas constructed by Wang et al. [ 114 ] are also of high reference value, although they do not cover all tissue types. A unified system will improve efficiency and applicability for other studies [ 146 ]. Clustree software can be used for determining whether the number of cell types obtained from clustering is appropriate [ 142 ]. Software that automatically annotates cell types can also assist in identifying cell types, e.g., Cellhint [ 146 ], CellTypist [ 147 ], and SingleR [ 148 ]. Software programs for the automated annotation of cell types have been developed based on mathematical models and are specific for annotating certain cell types. For example, Cellhint is used to annotate human cells, and CellTypist is only used to annotate human immune cells. Notably, bioinformatics analysis should be performed manually to ensure the biological significance of the annotated results.

Currently, single-cell transcriptome sequencing technology is cumbersome and costly in terms of experimental steps. Professional experimentation and specialized software support are required for all aspects, from sample preparation to data analysis. Moreover, the bias of cell capture during the sequencing process may lead to inaccurate results, which is mainly attributed to the possibility of missing or detecting specific types of cells at low frequencies. Moreover, bioinformatics tools and algorithms are still suboptimal, making it challenging to extract meaningful information from the massive amount of data. In the future, it will be necessary to simplify and optimize the process of single-cell technology to reduce its cost and operational difficulty and to make it easier to apply in different fields. The accuracy and efficiency of cell capture techniques should be improved to reflect the diversity of cellular communities. In the meantime, techniques for cell capture and mRNA enrichment in prokaryotes are still under development. The implementation of microbiome single-cell transcriptome technology will substantially broaden the application landscape of single-cell technology [ 149 ].

One of the greatest limitations of scRNA-Seq is the loss of spatial information due to tissue dissociation. Spatial transcriptomics is a more recently developed methodology that allows for the localization and construction of a cellular expression map with a spatial dimension, which is not achievable with scRNA-Seq. Coupled with scRNA-Seq, this approach can stereoscopically demonstrate the heterogeneous distribution and functional localization of individual cells and reveal spatial differences in cells during evolutionary development or disease onset. However, the application of this approach to domestic animals is still relatively rare. Only studies on the spatiotemporal transcriptional profiling of chicken heart development have been reported, but have revealed the pathways through which cardiac cell differentiation and morphological changes occur at the same time as spatially restricted regulatory programmes [ 150 ]. The complexity of life activities is difficult to determine by single-modality omics methods; therefore, single-cell multi-omics technologies, including single-cell transcriptome as the core analysis combined with genome, proteome and metabolome analyses, are inevitable [ 151 ] and will be able to deepen the understanding of cell type and state in greater dimension. For example, the dynamic changes of single-cell RNA/ATAC sequencing in porcine embryonic skeletal muscle were consistent with the activity of different cell type-specific transcription factors, which helped identify key regulators of muscle formation after integrative analysis [ 152 ].

Sequencing of certain animals or organs can be challenging due to their limited availability, difficulty in manipulation, or ethical concerns. Organoids, 3D cultures developed from stem cells that closely resemble the source tissue [ 153 ], are valuable in vitro tools for organoid single-cell transcriptomics in such cases. Integrating organoids with scRNA-Seq can allow more precise comparisons between organoids and source tissues in terms of cell types and gene expression patterns; moreover, through real-time monitoring of transcriptome changes in single cells of organoids cultured under different treatments, it is possible to provide potential cellular and molecular phenotypic information on complex traits, such as feed efficiency and disease resistance. Organoid models have been constructed for various livestock species [ 154 , 155 , 156 ] and are mainly used to study organ development, host–microbe interactions, cellular nutrient metabolism mechanisms, and drug toxicity. Zhang et al. [ 83 ] utilized a significant quantity of butyric acid to stimulate rumen organoids, and the organoids showed noticeable keratinization and significant increases in the expression levels of related keratinization genes. These findings were confirmed by single-cell sequencing, demonstrating the potential for combining single-cell transcriptomes and organoids for the study of biological mechanisms.

Single-cell transcriptomics reveals the role of different cells in organisms. However, it is important to recognize that in multicellular organisms, the functionality of the organism is dependent on synergistic interactions between different cells. Thus, single-cell transcriptome-based research should consider the relationships between cell lineages and the interactions between cells. This might also prevent an overemphasis on the functions of individual cells and might rather ensure that the influence of the hostile environment on cell development and function is not ignored. Using a multidimensional approach to single-cell transcriptome studies, such as cell communication analysis, the interaction network between cells can be reconstructed and predicted, revealing signalling and regulatory mechanisms and providing a more accurate reference for studying overall organism and tissue function. It is also possible to validate the accuracy of single-cell sequencing data through various biological experimental means, ensuring a more reliable assessment of research results.

Conclusions

Single-cell transcriptomics has enabled the analysis of heterogeneity in gene expression in tissues and organs at the single-cell level. This advancement has provided a robust framework for identifying cell types, discovering rare cell populations, screening marker genes, exploring cellular developmental trajectories, and analysing cellular functions. ScRNA-Seq has also been extensively applied in animal science, particularly in studies involving domestic species of high economic importance. Using scRNA-Seq, animal researchers have investigated topics such as nutritional regulation, metabolic mechanisms, spermatogenesis, embryonic development, genetic breeding, and disease mechanisms in livestock. Through the construction of single-cell atlases for different animal organs, researchers have revealed the intricate cellular heterogeneity and gene expression variability present at the individual, organ, and tissue levels. This approach has facilitated deeper mechanistic investigations at the molecular level, shedding light on the underlying genetic basis of important traits and disease pathogenesis. Consequently, scRNA-Seq has made substantial and significant contributions to advancing our understanding of animal biology and is ultimately poised to enhance the quality of livestock products to meet increasing consumer demands. When analysing single-cell transcriptomic data, the optimal sample size should be determined based on the biological variation, statistical significance, cost and complexity of the data analysis. Accurate cell clustering and cell type annotation should consider background knowledge, as well as appropriate and stable algorithms. Currently, scRNA-Seq still faces several great challenges, ranging from sample processing to data analysis, and the integration of novel experimental methodologies and sequencing technologies is needed to probe and elucidate the intricate regulatory networks and causal relationships among diverse biomolecules in a multidimensional manner. Through continued innovation and interdisciplinary collaboration, single-cell transcriptomics holds the promise of unlocking new frontiers in animal research and fostering sustainable advancements in agricultural productivity and animal health.

Availability of data and materials

Not applicable.

Abbreviations

Channel-gap-like

Endothelial-to-mesenchymal transition

Gastrointestinal tract

Peripheral blood mononuclear cells

RNA-Sequencing

Short-chain fatty acid

• Single-cell RNA sequencing

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Acknowledgements

We thank all the members in the Institute of Dairy Science, College of Animal Sciences, Zhejiang University.

This study was supported by the Natural Science Foundation of Zhejiang Province Outstanding Youth Fund Project (LR23C170001).

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Institute of Dairy Science, Ministry of Education Key Laboratory of Molecular Animal Nutrition, College of Animal Sciences, Zhejiang University, Hangzhou, 310058, China

Yunan Yan, Senlin Zhu, Minghui Jia, Xinyi Chen, Wenlingli Qi, Fengfei Gu, Teresa G. Valencak, Jian-Xin Liu & Hui-Zeng Sun

Key Laboratory of Dairy Cow Genetic Improvement and Milk Quality Research of Zhejiang Province, Zhejiang University, Hangzhou, 310058, China

Fengfei Gu & Hui-Zeng Sun

Agency for Health and Food Safety Austria, 1220, Vienna, Austria

Teresa G. Valencak

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YNY: Conceptualization, Writing–Original Draft, Visualization. SLZ: Conceptualization, Visualization. MHJ: Writing–Original Draft. XYC: Visualization. WLLQ: Visualization. FFG: Conceptualization, Writing–Review & Editing, Supervision. TGV: writing, reviewing, revising. JXL: Conceptualization, Writing–Review & Editing, Supervision. HZS: Conceptualization, Writing–Original Draft, Writing–Review & Editing, Supervision.

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Additional file 1.

. Applications of single-cell transcriptomics in animal science.

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Yan, Y., Zhu, S., Jia, M. et al. Advances in single-cell transcriptomics in animal research. J Animal Sci Biotechnol 15 , 102 (2024). https://doi.org/10.1186/s40104-024-01063-y

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Heavy metals, including lead, found in many dark chocolate bars, research shows

A new study finds that dark chocolate products sold nationwide may contain excessive amounts of heavy metals. 

The research, led by scientists at George Washington University and published Wednesday in the peer-reviewed Frontiers in Nutrition, examined over 70 dark chocolate products from retailers such as Whole Foods Market, Amazon and GNC. The products were tested to see whether the heavy metals lead, cadmium or arsenic were in them. 

Overall, 43% of the products studied exceeded acceptable levels of lead and 35% exceeded cadmium levels, according to the study, which was based on a California law that sets maximum allowable dose levels for heavy metals in food. Food researchers often use the 1986 regulations, known as Prop 65, as a safety standard because the Food and Drug Administration doesn’t set limits on heavy metals in most foods, said Leigh Frame, director of integrative medicine at George Washington University School of Medicine and Health Sciences and lead author of the study.

The FDA does have suggested limits for chocolate and sugar-based candy but only for children.

According to the California guidelines, the threshold for heavy metals in foods is 0.5 micrograms a day. For the study, the scientists estimated the number of micrograms a day people would be exposed to if they ate the suggested serving amounts on the chocolate product labels. They found that the chocolate samples ranged from 0 to as high as 3.316 mcg per daily serving. Levels of cadmium, a carcinogen at high levels, ranged from 0.29 to 14.12 mcg, with the limit being 4.1 mcg per day.

None of the products exceeded the maximum level for arsenic. 

Frame said that because the products had varying amounts of lead in them, limiting consumption is the only sure way to reduce exposure.

“Don’t have large amounts of chocolate every single day,” she said. “One ounce serving size is what we recommend, or maybe you have 2 ounces every other day.” 

How to avoid lead in foods

Researchers agree that avoiding heavy metals entirely in our diet is nearly impossible. Foods such as rice, fish, fruits and vegetables have been known to contain varying amounts of metals. While heavy metals can be naturally excreted by the body through sweat and urine, if they are consumed in high amounts they can accumulate in the body and damage major organs. 

“You actually cannot avoid exposure to heavy metals in the diet,” Frame said. “It’s really not about avoiding them; it’s about making sure you’re not getting too much.” 

She emphasized a diversity in diet to avoid excessive exposure to any particular substance.

“Not eating the same thing day after day is going to help protect you from many different things, including heavy metals,” she said.

The authors intentionally left out which brands had what concentrations of metals given that levels could vary even within the same company. Interestingly, the study found that organic cocoa products were more likely to have higher levels of cadmium and lead. 

“Organic food doesn’t necessarily mean that it’s been checked for exposure to toxic metals like lead, cadmium and arsenic,” said Manish Arora, vice chairman of the department of environmental medicine and climate science at the Icahn School of Medicine at Mount Sinai in New York City.   

“I think to most of the public ‘organic’ just means cleaner, and in this case it’s counterintuitive,” he said. 

Arora, who was not involved with the study, said that while the new research was strong, a big unknown with the paper is how the heavy metals got into the chocolate products in the first place. 

“Is it the processing, the farming or the type of soil or the fertilizer or any other farming process that they’re using?” he asked. “We are left not being sure where the metal actually entered the food chain.”

Previous research has found that lead and cadmium can enter dark chocolate through different ways. Cadmium comes primarily through the cacao plant’s taking it up from the soil, while lead can be introduced at various points in the manufacturing process, including the harvesting, drying and fermenting of the cocoa bean. 

There is no safe level of lead. While the FDA does not set limits for cadmium or arsenic, almost all of the chocolate bars in the study were below its recommended level for lead: 2.2 mcg a day for children under age 7 and 8.8 mcg a day for women of child-bearing age.

That contrasts with the California guidance because levels set by Prop 65 tend to be more conservative, Frame said.

Tewodros Godebo, an assistant professor of environmental health sciences at Tulane University School of Public Health and Tropical Medicine, said that in his opinion the Prop 65 standards are too conservative and may cause unnecessary panic. He has published his own study this year, in which his team tested over 100 chocolate products. 

Instead of the Prop 65 limits, Godebo's research used a method proposed by the Environmental Protection Agency that found levels of heavy metals in chocolate were not enough to be concerning to adults. The EPA commonly uses the formula, called the hazard quotient, to determine a substance’s toxicity. 

Still, he recommended consuming no more than an ounce of dark chocolate per day and limiting consumption for children and pregnant women. 

The new study did not examine milk chocolate, but theoretically it should have a lower risk of heavy metal contamination, Frame said. That is because the metals are believed to come from the cocoa powder itself, which is present in higher levels in dark chocolate. 

Akshay Syal, M.D., is a medical fellow with the NBC News Health and Medical Unit. 

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Nutrition and mental health: A review of current knowledge about the impact of diet on mental health

Mateusz grajek.

1 Department of Public Health, Department of Public Health Policy, Faculty of Health Sciences in Bytom, Medical University of Silesia in Katowice, Katowice, Poland

Karolina Krupa-Kotara

2 Department of Epidemiology, Faculty of Health Sciences in Bytom, Medical University of Silesia in Katowice, Katowice, Poland

Agnieszka Białek-Dratwa

3 Department of Human Nutrition, Department of Dietetics, Faculty of Health Sciences in Bytom, Medical University of Silesia in Katowice, Katowice, Poland

Karolina Sobczyk

4 Department of Economics and Health Care Management, Faculty of Health Sciences in Bytom, Medical University of Silesia in Katowice, Katowice, Poland

Martina Grot

Oskar kowalski, wiktoria staśkiewicz.

5 Department of Technology and Food Quality Evaluation, Department of Dietetics, Faculty of Health Sciences in Bytom, Medical University of Silesia in Katowice, Katowice, Poland

Applied psychopharmacotherapy and psychotherapy do not always bring the expected results in the treatment of mental disorders. As a result, other interventions are receiving increasing attention. In recent years, there has been a surge in research on the effects of nutrition on mental status, which may be an important aspect of the prevention of many mental disorders and, at the same time, may lead to a reduction in the proportion of people with mental disorders. This review aims to answer whether and to what extent lifestyle and related nutrition affect mental health and whether there is scientific evidence supporting a link between diet and mental health. A review of the scientific evidence was conducted based on the available literature by typing in phrases related to nutrition and mental health using the methodological tool of the PubMed database. The literature search yielded 3,473 records, from which 356 sources directly related to the topic of the study were selected, and then those with the highest scientific value were selected according to bibliometric impact factors. In the context of current changes, urbanization, globalization, including the food industry, and changes in people’s lifestyles and eating habits, the correlations between these phenomena and their impact on mental state become important. Knowledge of these correlations creates potential opportunities to implement new effective dietary, pharmacological, therapeutic, and above all preventive interventions. The highest therapeutic potential is seen in the rational diet, physical activity, use of psychobiotics, and consumption of antioxidants. Research also shows that there are nutritional interventions that have psychoprotective potential.

Inherent in urbanization and the accompanying technological and cultural development, the rush of life, the pursuit of self-actualization, and the resulting overstimulation and lack of time, affect the change in eating habits and the consumption of high-calorie and processed foods ( 1 ). We can consider them as factors influencing the development of civilization diseases, important from the point of view of public health. Among them, we cannot forget about depressive and anxiety disorders that are becoming a global epidemic ( 2 ). The number of people requiring assistance from a mental health professional is steadily increasing in Poland and worldwide. According to the International Health Metrics Evaluation (IHME), at the end of 2017, 13% of the world population suffered from mental disorders ( 3 ). The Wittchen et al. study shows that mental disorders affect 38% of the European population ( 4 ). By the end of 2019, about 1.6 million people in Poland had received psychiatric treatment ( 5 ). The situation was not improved by the COVID-19 pandemic and related sanitary restrictions, which led to the isolation of many people, with feelings of insecurity, sadness, anxiety, and misinformation ( 6 ). All this has made psychological and psychiatric help the most sought-after form of health support today. There are only about 4,300 practicing psychiatrists in Poland ( 7 ). Even fewer, only 455, are practicing child psychiatry specialists ( 8 ). Statistics are believed to be better in the psychological and psychotherapeutic support sector, although public opinion is still divided about this form of support. Moreover, registers of psychologists and psychotherapists are not common. The described phenomena lead to a transformation of the psychiatric care model and mental health support. The number of people receiving psychiatric treatment is expected to increase over the next decades. The applied psychopharmacotherapy and psychotherapy do not always bring the expected treatment result ( 9 ). As a result, other interventions are receiving increasing attention. In recent years, there has been a dramatic increase in research on the effects of nutrition on mental status, which may be an important aspect of the prevention of many mental disorders, and at the same time may lead to a reduction in the proportion of people with mental disorders.

Thus, this review aims to answer the question of whether and to what extent lifestyle and related nutrition affect mental health and whether there is scientific evidence supporting the diet and mental health relationship.

The question posed in the objective can be divided into specific questions according to which this review was divided.

Q1: Are there correlations between nutrition and mental health?

Q2: are there psychoprotective food ingredients, q3: are there nutritional interventions with proven preventive potential for mental disorders, review methodology, methodology background.

The main aspect that guided the review works conducted was to look for nutritional recommendations in the cited works regarding nutrition as psychoprophylaxis and dietary management of psychiatric disorders. Unfortunately, the current state of knowledge on this topic, despite many studies, is still poor, so the authors decided to conduct a broad review of the most current knowledge in this area to identify those sources that address the described topic and gather in one place the available knowledge.

Review procedure

The review was conducted following good practices associated with conducting similar reviews. Literature items were searched by a team of researchers (authors) along with a library staff member trained in literature searching and EBM (evidence-based medicine) and HTA (health technology assessment). A preliminary search for items consistent with the topic and purpose of the review was conducted to identify the research field. After reviewing existing data, a keyword package was selected that seemed most relevant and consistent with the review topic.

Eligibility criteria

The primary eligibility criteria were the language of publication, years of research or review, publication status, and whether the authors were specialists in their field (or had other publications in a similar field). Regarding language, English-language articles were selected because this language seems to be universal in the scientific community. In addition, articles that were published after 2005 were included to make sure that the topic addressed was not a completely new field of research, but also to avoid very old data, because as is known from common practice, dietetics, as well as mental health expertise, are two of the most rapidly developing scientific fields. Additionally, articles were selected that were available in full-text on an open-access basis and had impact factor values.

Search strategy

A review of the scientific evidence was conducted based on the available literature by entering sample phrases (consistent with the MeSh dictionary) with Boole operators, logical operators (and, or, not), and special characters,: “psychodietetics,” “nutripsychiatry,” “diet,” “mental health,” “lifestyle,” “body weight,” “obesity,” “depression,” “mental disorders” (and various combinations thereof) using the methodological tool of the PubMed database. The PubMed database in this regard seems most appropriate because it is a methodological tool that allows searching for articles available in multiple scientific databases (such as Medline or Embase). Its use provides the opportunity to meet all expectations from the review (transparency, clarity, comprehensiveness, focus, uniformity, accessibility, coverage of the entire topic).

Sources selection

The literature search yielded 3,473 records, from which 356 sources directly related to the topic of the study were selected, and then those with the highest scientific value were selected according to eligibility criteria.

The accuracy, objectivity, validity, and relevance of the evidence were tested using questions consistent with the GRADE scale: Is the information reliable? Is the information free of mistakes? Has the information been properly substantiated? Is it possible to verify the information against other reliable sources? Who are the authors? Are they qualified to present information on the topic? Are they affiliated with reputable institutions working on the issue? Is the data source peer-reviewed? For what purpose was the information? Is the information an evidenced-based fact or constitutes an opinion? Is the information subject to risk? Can this risk be estimated? When was the information published? Is the information current or outdated? Is the timeliness relevant to the issue at hand? Does the information cover the entire issue? Does the information contain background data or does it explore the issue in depth? The final literature review was based on 110 sources, representing mainly scientific output after 2005 and important multicenter studies performed after 2015. The data obtained from the review are presented in descriptive and tabular form. In addition, 11 additional sources were used in preparing the background of the research problem and the theoretical introduction.

Critical appraisal

In critically evaluating the sources, attention was paid to whether the articles appeared in peer-reviewed journals (by at least two reviewers) and whether they had an impact factor. As described above, 110 sources were eligible for final review. A limitation of the method adopted was primarily the exclusion of sources written in a language other than English. In addition, IF has many well-documented drawbacks as a research assessment tool and therefore is not the best way to evaluate the quality of individual research articles. Nevertheless, it was chosen because it is a synthetic indicator of a source’s impact on the field of science, and a journal that has it can more likely claim to be publishing credible scientific evidence. The review did not include so-called “grey literature”, i.e., literature that has not gone through the review process or that is internal to the university (theses, conference reports, government leaflets, newsletters, etc.). Despite their multiple values, these sources are characterized by a high risk of containing outdated knowledge ( Figure 1 ).

A flowchart of how to proceed in selecting bibliographic sources.

Excess body weight is certainly an important social problem today. More than 0.7 billion people worldwide are obese, this is about 30% of the total population, and the number of obesity-related deaths is constantly increasing ( 10 ). We consume more and more processed, high-energy, and nutrient-poor foods. Consequently, we face problems of overweight and obesity with concomitant nutrient deficiencies (quantitative malnutrition) ( 11 ). Although the level of calories consumed is increasing, we are not taking in the recommended values of micro- and macroelements that play a significant role in the proper functioning of our nervous system – B vitamins, zinc, and magnesium. Additionally, we consume less fiber- and nutrient-rich vegetables and cereal products than recommended ( 10 , 11 ). Superimposing smoking, limited physical activity, and harmful alcohol consumption to the above dietary patterns, adversely affect health and development of mental disorders, including depression ( 10 ). Whose nutritional prevention is well documented in the literature ( 12 ).

The antioxidant system, which has been implicated in the development of psychiatric disorders, is relevant here ( 13 ) and its proper functioning depends on the presence of nutrients in food. In addition, the concentration of brain-derived neurotrophic factor (BDNF), which is involved in plasticity and neurodegenerative processes, depends on nutrients ( 14 ). Findings indicate a reduction in the incidence of depression and suicide with a healthy eating pattern ( 15 , 16 ). Randomized trials are emerging that evaluate the efficacy of dietary change as a form of treatment for depression ( 15 – 17 ). Selective food supplementation can be beneficial in the treatment of psychiatric disorders. Among them, compounds such as S-adenosylmethionine, N -acetylcysteine, zinc, and B vitamins including folic acid, and vitamin D are mentioned. Also, omega-3 unsaturated fatty acids have a wide range of effects. They participate in synaptogenesis by influencing receptor degradation and synthesis. They have an anti-inflammatory effect and inhibit apoptosis. They affect cell membrane function, BDNF action, and neurotransmitter reuptake ( 18 ). S-adenosylmethionine (SAM) is a compound formed from adenosine and methionine, which plays a key role in methylation processes. The results of studies show its antidepressant effects ( 19 ). The use of N -acetylcysteine influenced the effectiveness of therapy in schizophrenia, bipolar affective disorder, or trichotillomania. It has anti-inflammatory, antioxidant, and neuroprotective effects ( 20 ). Zinc deficiency, in turn, has been linked to the severity of depressive symptoms, and its supplementation included with antidepressants plays a role in mood stabilization. Zinc modulates cytokine activity and influences neurogenesis by affecting brain-derived neurotrophic factor levels ( 21 ). B vitamins play a role in the proper functioning of the nervous tissue. Folic acid (vitamin B9) deficiency has been associated with depressive symptoms and determined in subjects with mediocre responses to antidepressants ( 22 ). Low vitamin D levels were associated with a higher risk of schizophrenia and depression ( 23 ). It has been proven that vitamin D supplementation for a period of 3 months (4,000 IU/day for 1 month and 2,000 IU/day for 2 months) significantly reduced the severity of depression, irritability, fatigue, mood swings, sleep difficulties, weakness, and ability to concentrate in adolescents diagnosed with depression. This effect is supported by studies on animal models – vitamin D contributes to the plasticity of synapses, has a neuroprotective effect, supports the production of neurotrophic factors such as nerve growth factor (NGF) and regulates the function of the dopaminergic system. ( 24 ).

For the review, the results of the most important studies on the psychoprotective effects of bioactive components contained in foods (vitamins, minerals, omega-3, and more). have been collected in tabular form ( Table 1 ).

Review of selected studies on the psychoprotective effect of probiotics.

Source: Own compilation based on literature review.

The gut microbiota is estimated to form a complex ecosystem containing 1,014 microorganisms. It contains 3.3 million genes and outnumbers the human genome by about 150-fold. At the same time, it is built by more than a thousand different species of microorganisms ( 25 ). The gut-brain axis describing the bidirectional relationship between the gastrointestinal tract and the central nervous system uses several communication mechanisms. Mutual exchange of information can occur via the autonomic nervous system and the vagus nerve ( 26 ). Many of the effects of probiotics on mental status are associated with information transmission via the vagus nerve ( 27 ). Results from germ-free (GF) mice cultured under sterile conditions, devoid of detectable microorganisms, demonstrate the involvement of the gut microbiota in the proper formation and function of the endocrine system by influencing the development of the hypothalamic-pituitary-adrenal axis. The response to a stress stimulus as measured by glucocorticosteroid and adrenocorticotropin levels was significantly elevated in GF mice. It was normalized after gastrointestinal colonization with the Bifidobacterium infantis strain ( 28 ). Additionally, stress affects the formation and diversity of intestinal microflora ( 29 ). Another link of communication is the immune system. The microbiota is involved in the proper development of the gastrointestinal mucosal immune system ( 30 ). Bacterial antigens such as polysaccharide A, lipopolysaccharides, and thymic acids shape its proper functioning ( 31 ). The microbiota also produces neurotransmitters: gamma-aminobutyric acid, butyric acid, serotonin, dopamine, and short-chain fatty acids, which can directly affect the nervous system ( 32 ).

So, can the psychoprotective effect of strains be used in nutritional intervention? It seems reasonable here to consider the possibility of implementing treatment with probiotic preparations containing selected bacterial strains that show positive effects on the human psyche. In this approach, “probiotic” is defined as living organisms that, when consumed in adequate amounts, have a beneficial effect on the functioning of the body ( 33 ). Ilya Metchnikov was awarded the Nobel Prize in 1908 for his research on probiotics. Among them, lactic acid bacteria are the most popular. Probiotics are mainly found in fermented dairy products, or pickled products ( 34 ). Prebiotics are non-digested food components whose fermentation in the gastrointestinal tract stimulates either bacterial growth or activity or affects both, leading to the development of beneficial intestinal microflora ( 35 ). Prebiotics can include ingredients such as inulin or fructooligosaccharides. Prebiotics may also have a beneficial effect by inhibiting the growth of pathogenic bacteria. Moreover, some research results show that prebiotics can reduce inflammation by modifying the composition of the microbiota ( 36 ). Synbiotics are ingredients that contain both prebiotics and probiotics. Such a constellation allows the use of synergistic effects of these preparations. In turn, psychobiotics are defined as microorganisms that are probiotics, that show positive effects in patients treated for mental disorders ( 37 ). They can often achieve their effect through the production of neurotransmitters such as gamma-aminobutyric acid, serotonin, or other substances with an effect on the cells of the nervous system such as short-chain organic acids: acetic, propionic, or butyric ( 36 ). Oral substitution of such probiotics as Lactobacillus helveticus and Bifidobacterium longum over a period of 1 month was associated with a reduction in symptoms of anxiety and depressive disorders and a reduction in stress levels as measured by the determination of cortisol levels in animal models ( 38 ). Currently, the most effective treatment of psychiatric disorders is achieved through the use of antidepressants, or antipsychotics. However, the additional use of psychobiotics to treat anxiety or depressive disorders may prove effective in the future. It is also worth noting that popular antidepressants and antipsychotics can affect the quality of gut flora and change the composition of the microbiome to a disadvantage by killing the cultures of bacteria living in the gastrointestinal tract ( 39 ).

For the review, the results of the most important studies on the psychoprotective effect of probiotics were collected in tabular form – Table 2 .

Review of selected studies on the psychoprotective effects of substances contained in food.

Factors such as genotype, intrauterine infections, developmental disorders, later traumatizing events, use of harmful psychoactive substances, and many others will influence the onset of psychiatric disorders. These factors influence not only the onset of the disorder but also its progression. Treating early conditions in psychiatry can result in a much better response to the treatment given and better functioning of patients. This fact can be particularly observed in studies on the early detection of psychotic disorders ( 40 ). Prevention in medicine, including psychiatry, requires knowledge of appropriate and useful tools that would allow detection of increased risk of mental illness and monitoring of the developing psychopathology of the disorder. McGorry et al. ( 41 ) proposed a four-stage model of the development of mental disorders. According to this model, serious mental disorders develop from high-risk states: grade 0 means the development of undifferentiated, general symptoms, such as slight anxiety, restlessness, depressive symptoms, or somatic symptoms lead to grade 1, in which types 1A and 1B can be distinguished according to their severity. Further progression of the disease results in the development of a first episode of the disorder and here we speak of stage 2, which is accompanied by persistent 7ncludims and frequent relapses. Grade 3 includes incomplete remission and regular and repeated relapses. Grade 4 in this context means treatment-resistant disorder. The worsening of a psychiatric disorder is determined by genetic and environmental factors, and it is the latter that seems to be the main target for preventive interventions in psychiatry. Some biomarkers in psychiatry are directly related to nutrition. The first of these is the hypothalamic-pituitary-adrenal axis (HPA). Reduced ability to cope with stress plays a role in the development of psychiatric disorders ( 42 ). It is known that traumatizing experiences in early childhood shape vulnerability to stress in later life ( 43 ). The normal functioning of the HPA axis is often altered in psychiatric disorders, and increased cortisol secretion is observed in affective and psychotic disorders. Additionally, antipsychotic drugs appear to decrease HPA axis activity ( 44 – 47 ). Furthermore, healthy individuals who were first-degree relatives of individuals with psychotic disorders were found to have HPA axis dysfunction with elevated cortisol levels ( 48 ). These studies show that the HPA axis appears to be an important biological marker of susceptibility to developing psychiatric disorders. In this context, its association with gut microbiota is not insignificant. Other potential biomarkers involved in the pathophysiology of psychiatric disorders are inflammation and oxidative stress ( 49 ). The inflammatory theory of depression development is gaining increasing attention, and elevated levels of proinflammatory cytokines are observed in depressive, psychotic, and manic states ( 50 , 51 ). Elevated levels of proinflammatory cytokines occur before the onset of de novo disorders, suggesting their role in the genesis of these disorders ( 52 ). An increase in oxidative stress in psychotic disorders with a decrease in glutathione and antioxidant enzymes has also been observed ( 53 ). The potential effectiveness of selective cyclooxygenase-2 antagonists in the treatment of bipolar affective disorder and schizophrenia has been demonstrated ( 51 , 54 ). The use of statins, which have anti-inflammatory and antioxidant properties, reduced the risk of depressive disorders ( 55 ). Polyunsaturated fatty acids are further potential biomarkers that may have applications in psychiatry. Omega-3 polyunsaturated fatty acids may play a role in the pathogenesis of affective and psychotic disorders ( 56 , 57 ). Their deficiency may be present in the early stages of psychotic disorders – stage 1b. Supplementation with omega-3 polyunsaturated fatty acids reduced the risk of psychotic disorders among individuals at high risk of developing them ( 58 ).

The intestinal barrier is composed of several layers, including the intestinal microflora, mucus layer, intestinal epithelium, and elements of the circulatory, immune, nervous, and lymphatic systems. The layer of epithelial cells, mainly enterocytes connected by tight junctions, is the most important for the intestinal barrier ( 59 ). Its main function is to regulate the absorption of nutrients, electrolytes, and water from the gastrointestinal lumen into the blood or lymphatic system and prevent the penetration of pathogens from the gastrointestinal lumen. Factors such as stress, pro-inflammatory factors, dysbacteriosis of the intestinal microflora, alcohol, or antibiotics may cause excessive permeability of the intestinal barrier ( 60 – 62 ). Currently, the microbiota and its diversity as a trigger for generalized inflammation are gaining great importance ( 61 ) Under the influence of the impaired functioning of the barrier, the migration of bacteria from the lumen of the gastrointestinal tract occurs, which activates the cells of the immune system affecting the functioning of the immune, endocrine and nervous systems ( 62 ). It has been observed that patients with depression have elevated IgA and IgM immunoglobulins against lipopolysaccharides of the bacterial microbiome ( 63 ). The current study indicates the use of a dietary inflammatory index, which assesses the effect of the entire diet or individual dietary components on the concentration of inflammatory markers. The results of a systematic review by Chen et al. ( 64 ) indicate that a higher dietary inflammatory index is associated with an increased risk of common psychiatric disorders, including symptoms of depression, anxiety, distress, and schizophrenia. Of particular importance is the novel finding from the dose-response analysis that a 1 unit increase in the dietary inflammatory index was associated with a 6% higher risk of depressive symptoms. Similar relationships have been observed by Firth et al. ( 63 ), particularly in schizophrenia – individuals who consume more pro-inflammatory foods and less anti-inflammatory foods are more predisposed to psychiatric disorders. At this point, it is important to look at the relationship between diet and the proper functioning of the intestinal barrier. It turns out that it is not without significance in maintaining homeostasis. A diet consisting of fast food and highly processed foods is associated with increased intestinal barrier permeability ( 65 , 66 ).

Epidemiological studies have shown that diet impacts mental health, and intervention studies confirm this relationship ( 17 ). The challenge for “nutritional psychiatry” is to produce comprehensive, consistent, and scientifically rigorous evidence-based studies that define the role of diet and nutrients in different aspects of mental health ( 67 – 70 ). Overall, few randomized trials investigate the effectiveness of dietary change in mental health treatment. One intervention study to date involved a 12-week Mediterranean diet. This study reported significant improvements in mood and reduced anxiety in adults with major depression ( 71 ) More recent RCTs – HELFIMED ( 72 ) and PREDI_DEP ( 73 ) have confirmed the benefits of a Mediterranean-style diet for mental health in depression. In contrast to these studies, in the MooDFOOD RCT, multiple nutrient supplementation did not reduce episodes of major depression in overweight or obese adults with subsyndromal depressive symptoms. This study found that multinutrient supplements containing omega-3 PUFAs, vitamin D, folic acid, and selenium neither reduced depressive symptoms, anxiety symptoms nor improved health utility indices ( 74 ). Similar results regarding the lack of effect on mental state improvement were obtained in a review of the literature in the context of vitamin D ( 75 ). For omega-3 PACs, one RCT including people with mild to moderate depression found no beneficial effect of omega-3 PACs on depressive symptoms ( 76 ). No effect of folic acid supplementation in combination with vitamin B 6 and B 12 on the onset of depression was found in older men ( 77 ) and older women ( 78 ). Furthermore, Rayman et al. ( 79 ) found no effect of selenium supplementation on mood in older people. Overall, the studies available to date, do not support the use of nutritional supplementation to prevent depression.

However, many studies confirm that higher dietary quality in adulthood is associated with a reduced risk of cognitive decline ( 17 ). Additionally, the intake of antioxidant polyphenols in older adults is associated with improved cognitive ability ( 80 – 82 ). Another study showed that a Mediterranean diet supplemented with olive oil and nuts was associated with improved cognitive function in an older population ( 83 ).

Therefore, we undertook an analysis of diets that could potentially affect mental health such as the MIND diet, the Mediterranean diet, and the ketogenic diet.

The MIND diet is a dietary recommendation to counteract neurodegenerative brain changes and improve nervous system function. This diet is beneficial for cognitive decline in the aging process, as well as for the prevention and progression of neurodegenerative diseases, including Alzheimer’s disease ( 84 ). The MIND diet combines the principles of the Mediterranean diet and the DASH diet, which are based on a high intake of vegetables, fruits, nuts, whole grain cereal products, olive oil, fish, and seafood, and moderate consumption of dry red wine with meals ( 85 ). Studies prove the positive effects of the DASH and Mediterranean diets on other diseases such as diabetes, cancer, and obesity ( 86 – 89 ).

Long-term observations confirm that adherence to the Mediterranean diet reduces the risk of developing neurological disorders by up to 28% compared to the use of other diets ( 83 ). Adherence to the MIND diet was significantly associated with a lower chance of depression and psychological distress, but not anxiety, in the entire study population ( 90 ). Like the Mediterranean diet and the DASH diet, the MIND diet emphasizes natural plant-based foods and limited intake of animal and high-fat foods, especially of animal origin. However, there are some differences between the MIND diet and the DASH diet, and the Mediterranean diet. For example, leafy green vegetables and especially berries are unique components of the MIND diet that are not included in the Mediterranean and DASH diets ( 90 ). The MIND diet does not focus on a high intake of fruit, dairy products, and potatoes. Another difference between MIND and the DASH and Mediterranean diets concerns fish consumption. In MIND, individuals consuming as little as 1 portion of fish per week receive a positive result, whereas, in the Mediterranean and DASH diets, larger amounts of fish would need to be consumed to achieve a result ( 91 ). The MIND diet significantly slows cognitive decline with age ( 92 ). The Mediterranean diet has also been shown to have a protective effect on anxiety and mental stress ( 93 ).

Mental illnesses are associated with numerous metabolic disorders in the brain and co-occur with many other metabolic disorders such as obesity, diabetes, and CVD. The ketogenic diet is an evidence-based treatment for epilepsy that has been shown to have profound effects on brain metabolism and neurotransmitter function. In a ketogenic diet, as much as 80 percent of energy can come from fat. This proportion sounds like a deal-breaker for healthy eating, but it turns out that ketones formed from fats can alleviate epileptic seizures unresponsive to anticonvulsant drug therapy ( 83 ). In the case of mitochondrial epilepsy, reports on the effects of the ketogenic diet are conflicting. In a study by El Sabbagh et al. ( 94 ), no patients on a ketogenic diet achieved no significant reduction in seizure frequency epileptic seizures. In contrast, a study by Kang et al. ( 95 ) involving 14 patients showed that the use of a ketogenic diet in 10 of them reduced the frequency of epileptic seizures by more than 50%, and in 7 patients, epileptic seizures ceased. In the analysis, there were improvements in symptoms including mood, cognitive function, communication skills, energy, anxiety, and auditory and visual hallucinations ( 90 ). Other reported benefits included positive biometric changes such as improvements in lipid profile, weight reduction, positive change in blood glucose, and reduction in HbA1c. These benefits may facilitate the management of comorbidities and improve overall health and well-being ( 93 ). This highlights that advances in nutritional psychiatry are important and it will be important to replicate, refine and scale up dietary intervention studies targeting the prevention and treatment of common mental health disorders. In addition, there is an unmet need for more randomized, controlled clinical trials ( 118 – 121 ).

Strengths and limitations

There is still little work in the scientific space that summarizes the major findings related to the impact of nutrition on mental health, especially, as this review does, highlighting the importance of nutrition in psychoprevention and pointing to the psychoprotective effects of nutrients. The primary limitation of the presented review of research on the relationship between diet and mental health is the plethora of studies on the topic. The plethora of studies here does not mean that they all address the issue presented in this manuscript. Much of the work that was searched and queried assumes a relationship between nutrition and the psyche, but these tend to be very superficial opinions that are not scientifically grounded. The authors are aware that in the face of such a large body of research, important reports may have been overlooked, but it should be noted that every effort was made to ensure that this review was conducted fairly, taking into account large, multi-center research projects and highlighting the major research streams in psychodietetics and nutripsychiatry.

Additionally, it was observed that in the current state of scientific knowledge, few large meta-analyses are treating the effects of food and diet on mental health. Therefore, it is difficult to discuss the effectiveness of introducing nutritional interventions among people with mental disorders or treating nutrition as the only means of prevention. Furthermore, the primary threat to interventions of this type is the difficulty in monitoring dietary patterns or intake of specific components. In addition, their absorption and metabolism are also dependent on many factors that rarely have a consistent course. Therefore, it is postulated that further research should be directed toward the creation of unambiguous dietary recommendations for mental health problems.

In recent decades, the relationship between nutrition and patients’ mental status has been underappreciated, as evidenced by the lack of research conducted before the 21st century in this area of knowledge – cited in this review. In recent years, this trend has been reversed, with research in psychodietetics and nutripsychiatry gaining popularity. In the context of current changes, urbanization, globalization, including the food industry, and changes in people’s lifestyles and eating habits, correlations between these phenomena and their impact on psychological status are becoming important. Exploring these correlations creates potential opportunities to implement new effective dietary, pharmacological, therapeutic, and above all preventive interventions ( Figure 2 ).

Links between nutrition and mental health.

Author contributions

MATG: conceptualization. MATG and KK-K: investigation and methodology. KS and AB-D: data curation. MATG: writing – original draft preparation. MATG, KK-K, MARG, and AB-D: writing – review and editing. KS and AB-D: supervision. KK-K: project administration. WS: conducting an additional literature review, creating tables summarizing current knowledge of psychobiotics and psychoprotective food ingredients, and revising the work. All authors contributed to the article and approved the submitted version.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

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