The Effect of Diet on Mental Health

The brain controls and regulates most of the body’s vital functions, conscious or not. For this reason, it is essential that the brain receives a steady supply of fuel and oxygen. The fuel is obtained by metabolizing nutrients made available in the bloodstream, originating in the digested food.

The brain consumes 20% of the daily intake of calories, that is, about 400 (out of 2000) calories a day. Structurally, about 60% of the brain is fat, comprising of high cholesterol and polyunsaturated fatty acids (PUFAs).

Thus, the food one eats is directly linked to brain structure and function, and thus affects the working of the mind. Many studies have found that diets that are too rich in refined sugars are toxic to brain functioning because the high content of simple sugars stresses the pancreas and induces insulin resistance. The high sugar levels with compensatory insulin responses stimulate the counter-reactive surge of autonomic neurotransmitters like cortisol and glucagon.

These are known to produce increased anxiety, hunger and irritability. Moreover, they induce inflammatory and oxidative stress. This has been linked to an exacerbation of symptoms of depression and other mood disorders. These findings have led to the emerging field of nutritional psychiatry that traces relationships between food, feelings, gut microbiota, and human behavior.

Deficiency disorders and mood

The deficiency of nutrients like cobalamine, folate and zinc is known to be associated with symptoms of depression and dementia, cognitive decline and irritability. Both overeating and food insecurity are associated with mood and anxiety disorders.

Mental illness is ranked among the largest contributors to the global health burden, especially depression, which accounts for the major chunk of disability in the more developed countries, especially in the age group of 15-44 years. Therefore, it is crucial to explore nutritional strategies to ameliorate these conditions.

Not only do people eat differently when anxious or depressed, but these changes may occur in either direction. Conversely, depression may be the result, at least partly, of poor eating habits, or may become worsened by the inability of the patient to stop eating comfort foods and choose a healthy diet. Such inability may be financial, psychological, or iatrogenic.

Serotonin and the gut

Serotonin is a monoamine neurotransmitter that helps to control sleep and appetite, inhibit pain, and to regulate mood. About 95% of the serotonin is produced in the gut, which is rich in neurons – the enteric plexus contains a hundred million nerve cells. Thus, the gut is intimately involved in emotional regulation, pain perception, and vital physiological functions.

Interestingly, the function of these neurons and their secretion of serotonin, and other neurotransmitters, is closely regulated by the metabolic byproducts of the trillion or so bacteria that comprise the gut microbiome. These bacteria ensure epithelial barrier integrity for the intestine, preventing the entry of bacterial toxins and pathogens into the systemic circulation. They also prevent the spread of inflammation beyond the gut lumen, enhance nutrient absorption, and activate gut-brain neural pathways – the gut-brain axis.

Monoamine neurotransmitters are synthesized from amino acids in a process that is mediated by mineral-dependent cofactors. Both folate and vitamin B12 are essential for the methylation that occurs during these synthetic processes, also regulating the formation of homocysteine – a metabolite that is strongly linked to cardiovascular risk and depression.

Dietary fats and brain functioning

Anti-inflammatory fats such as omega-3 fatty acids (FAs) are known to be essential components of neuronal cell membranes, and also play a role in many vital neural processes such as neurotransmission, gene expression, neurogenesis and neuronal survival. They are also known to have antioxidant properties.

Omega-3 FAs are used to treat a number of psychological disorders, including attention-deficit hyperactivity disorder (ADHD), depression, bipolar depression and post-traumatic stress disorder (PTSD). A high omega-6 proportion is linked to a higher incidence of these conditions, especially the first two.

The standard Western diet is rich in omega-6 but low in omega-3 FAs, primarily because of the consumption of refined flours and sugars, and highly processed foods, and low amounts of seafood (including fish) and grass-fed beef.

Some studies have confirmed that diets that are richer in healthier carbohydrates and fats, and lower in refined and highly processed foods, such as the Japanese and Mediterranean diets, are linked to a reduction in the incidence of depression by anywhere between a quarter to over a third, compared to the standard American diet.

Inflammation and the diet

Inflammation of the nervous system is also important in the pathogenesis of mental illness, and this is also linked to the diet. Many biomarkers of inflammation, such as C-reactive protein (CRP) and tumor necrosis factor alpha (TNF-α) were associated with a dietary pattern that was linked to a higher risk of depression over the next decade or so. This pattern included high simple sugars (sweetened drinks and refined flours), red meat and margarine (saturated fats), and little green or yellow vegetables, coffee, wine, or olive oil, which are all features of the stereotypical Western diet.

The high content of vegetables, fruits, grains, and seafood, with less dairy and meat content, and no refined foods, of the Mediterranean and Japanese diets, compares very favorably with the Western diet. The former uses small amounts of red wine and cheese or yogurt in the daily diet. The mechanism is thought to be via the brain-derived neurotrophic factor or BDNF.

This important molecule is implicated in the plasticity and survival of neurons, and neurogenesis. It is reduced in many mental health conditions including depression, PTSD and schizophrenia, and is affected by many antidepressants that are commonly prescribed.

Not only so, but the former presents many of the fruits and vegetables in fermented form, which provides probiotics protecting the gut by enhancing the content of health-promoting gut microbes and reducing or preventing inflammation throughout the body.

Thus, including more foods with omega-3 FAs in the diet when on inflammation-inducing medications, not only prevents inflammatory changes but also prevents the induction of depression in such individuals, according to recent, admittedly early, work. Again, the Mediterranean diet promotes gut microbes that produce anti-inflammatory metabolites.

Of course, depressive tendencies or stressors may prevent the beneficial effects of healthy food from manifesting themselves as reduced inflammation or improved mood. Secondly, only some depressed individuals show this inflammatory tendency, which may mean that diet plays this role in only a proportion of people, perhaps with other inflammatory conditions or due to constitutional factors.

Conclusion

Many experts would recommend that people pay attention to the relationship between their diet and the foods they eat over a month or at least two weeks. If they could reduce or eliminate processed foods and sugars for this period of time, before bringing back these foods one by one, it would be instructive to notice how they feel.

Better eating strategies are essential to promote mental health and recovery from mental illness. It was over 2,000 years ago that the famous Greek physician Hippocrates said, “Let thy food be thy medicine and thy medicine be thy food.”

Not only does the Mediterranean (and similar) diet affect the availability of the basic building blocks of the brain and neurotransmitters, including myelin, the neuronal membrane, and monoamine neurotransmitters, but it modulates key chemicals like BDNF to alter neuroplasticity, mutes system inflammation, and determines the health and state of the gut microbiome.

Many such traditional diets are known to include mostly nutritious whole foods without much processing. The role of a dietary specialist in helping patients with mentally ill-health to choose approaches that promote the ability to take care of oneself and enhance one’s health is very important and should be encouraged.

As one set of authors comment,

This message supports the idea that creating environments and developing measures that promote healthy, nutritious diets, while decreasing the consumption of highly processed and refined “junk” foods may provide benefits even beyond the well known effects on physical health, including improved psychological wellbeing.”

Further Reading

• All Mental Health Content
• World mental health support and the effect of stigma and discrimination
• A Guide to Coping with Change
• Managing and Reducing Stress
• Analyzing the Stigma Surrounding Mental Health

References

• Lachance, L. et al. (2015). Food, Mood, and Brain Health: Implications for the Modern Clinician. Missouri Medicine. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6170050/. Accessed on December 13, 2021.
• Firth, J. et al. (2020). Food and Mood: How Do Diet and Nutrition Affect Mental Wellbeing? The British Medical Journal. https://doi.org/10.1136/bmj.m2382. Available at: https://www.bmj.com/content/369/bmj.m2382. Accessed on December 13, 2021.
• Selhub, E. (2020). Nutritional Psychiatry: Your Brain on Food. Available at: https://www.health.harvard.edu/blog/nutritional-psychiatry-your-brain-on-food-201511168626. Accessed on December 13, 2021.

Written by

Dr. Liji Thomas

Dr. Liji Thomas is an OB-GYN, who graduated from the Government Medical College, University of Calicut, Kerala, in 2001. Liji practiced as a full-time consultant in obstetrics/gynecology in a private hospital for a few years following her graduation. She has counseled hundreds of patients facing issues from pregnancy-related problems and infertility, and has been in charge of over 2,000 deliveries, striving always to achieve a normal delivery rather than operative.