We all know that what we eat has an impact on our physical health, but what about our mental health? A growing body of research since the 1990s suggests that nutrition can play a key role in mental health, including major mental illnesses. This ought not to surprise us; after all, what we eat and drink provides the basis for every cell in our body. But how exactly does diet affect mental health?
The brain-gut axis
There is a strong communication link between our digestive system and the brain. It is a sort of two-way street called the brain-gut axis, with serotonin as a key neurotransmitter at both ends.[1 ,6] Serotonin carries messages between neurons, and has long been recognized as playing a role in a number of mental illnesses.
An unhealthy digestive system has a negative effect on brain function and mental health through this axis. Specifically, inflammation and microbial imbalance in the gut (dysbiosis) have been linked to several mental illnesses.
When diet, stress, or antibiotics challenge the microorganisms in the gut, a state of imbalance occurs. This results in increased permeability of the intestine, allowing molecules and bacteria to leak into the circulatory system. Gastrointestinal inflammation also causes the release of neurotransmitters and small proteins called cytokines, which in turn make the blood-brain barrier more permeable. These substances are detrimental to the immune system and brain function.
The body’s ability to detoxify is also affected by poor gut health, resulting in production of substances that damage all parts of the cell. This “oxidative stress” is thought to be involved in several disorders including ADHD, chronic fatigue syndrome, and depression.
Which mental illnesses have been linked to poor gut health?
A number of studies have found links to attention-deficit hyperactivity disorder (ADHD), autism, depression, anxiety, and psychosis.[2,3,6,8,9]
How can diet improve mental health?
The research strongly supports the role of certain foods in improving both GI health and mental health:
• Probiotics (supplements containing good gut bacteria) which restore the microbial balance in the gut. These also prevent or reduce physiological damage related to stress. Probiotics can be found in yogurts and cultured dairy products.
• Prebiotics which promote growth of good bacteria in the gut. Sources of prebiotics include whole grains, onions, bananas, garlic, honey, leeks, artichokes, fortified foods and dietary supplements.
• Omega-3 has anti-inflammatory properties as well as effects on transmission of serotonin and dopamine. 
• Vitamins and minerals: deficits in Vitamin D and folate are associated with worse symptoms in schizophrenia.
Specific diet patterns have been shown to have an effect on mental illnesses:
• Children and adolescents who consumed fewer vegetables, fruit, pasta, rice and fatty fish were more likely to be diagnosed with ADHD in a study of the Mediterranean diet. This same study found that diagnosis of ADHD was also associated with high consumption of sugar, candy, and soft drinks.
• Adults with ADHD who took a vitamin & mineral formula with no omega-3 experienced improvement in symptoms.
• An analysis of 21 studies from 10 countries found that a diet with high intake of red and/or processed meat, sweets, high-fat dairy products, butter, potatoes, refined grains and high-fat gravy, along with low intake of fruits and vegetables was associated with a higher risk of depression. A diet including low intake of red meat and high consumption of fruit, vegetable, whole grain, fish, olive oil and low-fat dairy was associated with lower risk of depression.
• Youth with depression benefited from a combination of omega-3 fatty acid supplements and Individual-Family Psychoeducational Psychotherapy.
Nutraceuticals: The Future of Mental Health Treatment
Dietary treatment is being touted as the future of mental health treatment. A whole field of Nutritional Psychology/Psychiatry is growing. Foods that have medicinal benefit are termed nutraceuticals and may be “prescribed” as an adjunct to other therapies. With our new awareness that the brain can indeed change and heal, and the role of diet in brain function, we are at an exciting threshold of discovery. There is hope for improvement and recovery in mental illness.
1. Clapp, M., Aurora,N. Herrera, L., Bhatia, M., Wilen, E , & Wakefield, S. (2017). Gut microbiota’s effect on mental health: The gut-brain axis. Clinics and Practice, 7(4), 987. DOI: http://doi.org/10.4081/cp.2017.987
2. Firth, J., Carney, R., Stubbs, B., Teasdale, S.B., Vancampfort, D., Ward, P.B., Berk, M & Sarris, J. (2017) Nutritional deficiencies and clinical correlates in first-episode psychosis: A systematic review and meta-analysis. Schizophrenia Bulletin, sbx162 DOI:https://academic.oup.com/schizophreniabulletin/advance-article/doi/10.1093/schbul/sbx162/4675234
3. Fristad, M.A., Vesco, A.T., Young, A.S., Healy, K.Z., Nader,E.S., Gardner, W., Seidenfeld, A.M., Wolfson, H.L. & L. Arnold, L.E. (2016) Pilot randomized controlled trial of Omega-3 and Individual–Family Psychoeducational Psychotherapy for children and adolescents with depression, Journal of Clinical Child & Adolescent Psychology, 45. DOI: 10.1080/15374416.2016.1233500
4. Kaplan, B.J., Rucklidge, J.J., Romin, A., & McLeoad, K. (2015). The emerging field of nutritional mental health. Clinical Psychological Science, (3)6, pp964-980. DOI: http://journals.sagepub.com/doi/abs/10.1177/2167702614555413
5. Li, Y., Lv, M-R, Wei, Y-J, Sun., L., Zhang, J-X, Zhang, H-G & Li, B. (2017) Dietary patterns and depression risk: A meta-analysis. psychiatry Research, 253, 373-382. DOI: https://doi.org/10.1016/j.psychres.2017.04.020
6. O’Mahoney, S.M., Clarke, G., Borre, Y.E., Dinan, T.G. & Cryan, J.F. (2017) Serotonin, tryptophan metabolism and the brain-gut-microbiome axis. Behavioural Brain Research, 277. DOI: https://doi.org/10.1016/j.bbr.2014.07.027
7. Rios-Hernandez, A., Aida, J.A., Farran-Codina, A. Ferreira-Garcia, E., & Izquierdo-Pulido, M. (2017) The Mediterranean Diet and ADHD in children and adolescents. Pediatrics, 139(2) e20162027; DOI: 10.1542/peds.2016-2027.
8. Rucklidge, J., Frampton, C., Gorman, B., & Boggis, A. (2014). Vitamin–mineral treatment of attention-deficit hyperactivity disorder in adults: Double-blind randomised placebo- controlled trial. British Journal of Psychiatry, 204(4), pp306-315. DOI:10.1192/bjp.bp.113.132126
9. Van Houtum, LAEM & Berend Deijen, J. (2016) The use of nutraceuticals as mono- or adjuvant therapy to pharmacothera[ies in major depressive disorder. International Neuropsychiatric Disease Journal, 8(2). DOI: http://www.journalrepository.org/media/journals/INDJ_29/2016/Oct/Deijen822016INDJ29568_1.pdf
10. Young, A.S., Arnold, E., Wolfson, H. & Fristad, M.A. (2017) Psychoeducational psychotherapy and Omega-3 supplementation improve co-occurring behavioural problems in youth with depression: results from a pilot RCT. Journal of Abnormal Child Psychology, 45(5) pp. 1025-1037. DOI: https://doi.org/10.1007/s10802-016-0203-3