Rates of mental health disorders in the US might be higher than average—it is estimated that around four percent of the global population experience depression—but these are by no means exclusively American problems.² Approximately 280 million worldwide suffer from depression, and more than 700,000 annual deaths result from suicide, a leading cause of death in adolescents and young adults.

This epidemic is not just feelings. It is also physical. The evidence of a bidirectional relationship between emotional/psychological health and physical health is plentiful. For example, we know that those who are depressed are more likely to be obese, and the prevalence of obesity increases as depression becomes more severe.³

How Does This Work?

We can intuitively understand that if we feel depressed, we may not make the best choices. To medicate our anger, loneliness, stress, and depression, we may turn to hyper-palatable foods. These foods, high in processed sugars and fats, trigger pathways involved in feelings of happiness, including our dopamine and serotonin pathways. Being low on serotonin, as we would be during depressive episodes, it makes sense that we would try to fill the serotonin deficit with a tasty jelly donut or, better yet, three or four.

This response is common and understandable. If we are honest, we can all relate to this behavior. We even have a phrase for it—eating your feelings.

But think about causality in the other direction. In other words, what if depression not only causes unhealthy food and lifestyle choices but also results from unhealthy food and lifestyle choices?

What Does the Research Show?

People who are obese have suppressed dopamine pathways. The more obese they are, the more limited are their dopamine receptors.⁴ This limitation means that they need more stimulus (e.g., more hyper-palatable food) to get the dopamine surge required to achieve what we might call satisfaction. We now know from animal experiments that sugar diets can alter chemical receptor activity in the brain, a process sometimes called neuroadaptation.⁵ It turns out that hyper-palatable foods may well be altering the chemical pathways involved in happiness.

In one study of older adults without depression followed for over seven years in Chicago, those who adhered to a more plant-based, Mediterranean diet (more fruits, vegetables, whole grains, legumes, fish, and olive oil and less meats and high-fat dairy) had lower rates of new depressive symptoms.⁶ This finding was similar to that of a study in Spain.⁷

We know that metabolic syndrome and various psychological disorders often occur together and that they share features like increased levels of chronic inflammation and dysregulated hormone systems.⁸ Both of these features are affected by diet and lifestyle.

In one of the intriguing experiments from Dr. T. Colin Campbell’s research, simply changing the amount of protein in the diet was found to affect physical activity in rats. And it is not how one might expect—the rats consuming lower amounts of protein voluntarily exercised more.⁹

One study put all this information to the test in a small two-week pilot study; they found that omnivores who avoided fish and other meat (including poultry) for two weeks improved in some measurements of mood, including stress.¹⁰

All things are connected: physical, mental, and emotional health; nutrition and physical activity; spirituality and social connection; animal welfare, environmental sustainability, and more. These are interconnected issues that researchers and consumers have recently grown more accepting of. This acceptance is especially evident in the interest in gut health, a major hot topic, and the mounting research on the microbiota-gut-brain axis.¹¹ We have known that dietary choices affect the gut for a long time. What is fascinating is how a healthy gut may, in turn, affect so much else, including major depressive disorder, anxiety, sleep disorders, attention-deficit hyperactivity disorder (ADHD), and Parkinson’s disease.^12–14

To summarize, although mental illness may drive unhealthy lifestyle choices, it is also likely that harmful food choices drive mental illness. In addition to eating our feelings, we often feel what we eat. This subtle but powerful shift in how we think about mental illness opens the door to a more substantial role for diet in treating depression than we currently acknowledge.

Additional Resources

• What Can I Eat to Help Fight Depression and Anxiety?
• Can You Boost Your Brainpower with Plant-Based Nutrition?
• The Psychological Toll of Living with Preventable Disease
• The Impact of Stress on Health and Disease

References

1. Brody DJ, Gu Q. Antidepressant use among adults: United States, 2015–2018. NCHS Data Brief, no 377. Hyattsville, MD: National Center for Health Statistics. 2020.
2. World Health Organization (WHO). Depressive disorder (depression). March 31, 2023. https://www.who.int/news-room/fact-sheets/detail/depression
3. Pratt L, Brody D. Depression and Obesity in the U.S. Adult Household Population, 2005–2010. NCHS Data Brief, No. 167. Hyattsville, MD: National Center for Health Statistics. 2014.
4. Wang GJ, Volkow ND, Thanos PK, Fowler JS. Similarity between obesity and drug addiction as assessed by neurofunctional imaging: a concept review. Journal of addictive diseases 2004;23:39-53.
5. Avena NM, Rada P, Hoebel BG. Sugar and fat bingeing have notable differences in addictive-like behavior. The Journal of nutrition 2009;139:623-8.
6. Skarupski KA, Tangney CC, Li H, Evans DA, Morris MC. Mediterranean diet and depressive symptoms among older adults over time. J Nutr Health Aging 2013;17:441-5.
7. Sanchez-Villegas A, Delgado-Rodriguez M, Alonso A, et al. Association of the Mediterranean dietary pattern with the incidence of depression: the Seguimiento Universidad de Navarra/University of Navarra follow-up (SUN) cohort. Arch Gen Psychiatry 2009;66:1090-8.
8. Nousen EK, Franco JG, Sullivan EL. Unraveling the mechanisms responsible for the comorbidity between metabolic syndrome and mental health disorders. Neuroendocrinology 2013;98:254-66.
9. Krieger E, Youngman LD, Campbell TC. The Modulation of Aflatoxin B1 (AFB1)-Induced Preneoplastic Lesions by Dietary Protein and Voluntary Exercise in Fischer 344 Rats. FASEB Journal 1988;2:3304.
10. Beezhold BL, Johnston CS. Restriction of meat, fish, and poultry in omnivores improves mood: a pilot randomized controlled trial. Nutr J 2012;11:9.
11. Mayer EA, Nance K, Chen S. The Gut-Brain Axis. Annu Rev Med. 2022;73:439-453. doi:10.1146/annurev-med-042320-014032
12. Góralczyk-Bińkowska A, Szmajda-Krygier D, Kozłowska E. The Microbiota-Gut-Brain Axis in Psychiatric Disorders. Int J Mol Sci. 2022;23(19):11245. Published 2022 Sep 24. doi:10.3390/ijms231911245
13. Socała K, Doboszewska U, Szopa A, et al. The role of microbiota-gut-brain axis in neuropsychiatric and neurological disorders. Pharmacol Res. 2021;172:105840. doi:10.1016/j.phrs.2021.105840
14. Wang Z, Wang Z, Lu T, et al. The microbiota-gut-brain axis in sleep disorders. Sleep Med Rev.2022;65:101691. doi:10.1016/j.smrv.2022.101691