The biggest contributor to mortality globally is a poor diet. Depression and anxiety, which often have a comorbidity with substance abuse, are the largest of the depressive disorders. The effects of diet on physical and mental health are well documented. In fact, over the last five years, close to 4,000 articles have been published on microbiota and gut health. The gastrointestinal system is the largest immunity organ of the body. This article will take a look at the links between gut health and mental health.
What are the Gut Microbiota?
Gut microbiota are microorganisms that are present in the gut. There are 1014 different types of gut microbiota, 10 times the number of human cells and 2/3 of these are specific to each person. They are like our identification, with more than 3 million genes. That is 150 times more than human genes. Their functions include aiding digestion, production of vitamin B and K, fighting against other microorganisms to maintain intestinal health and supporting the immune system (1).
There are over 1,000 species of these microbiota and certain species of these bacteria have a role in the production of organic chemicals that are known as neurotransmitters.
Some of these neurotransmitters include:
- Norepinephrine: Acts as an energy providing catecholamine.
- Serotonin: Primarily produced and found in the gut and central nervous system and helps regulate body processes, constrict smooth muscle and contributes to well-being and happiness.
- Dopamine: Produced is several areas of the brain and helps control the brain’s reward and pleasure centres and regulates movement and emotional responses.
- Tryptophan: An essential amino acid that the body cannot produce and must be obtained via the diet, which acts as a precursor for serotonin and melatonin production.
How does this impact Mental Health?
The vagus nerve is a direct connection between the brain and the stomach and transmits changes in hormones, neurones and bacterial alterations in the bowel to the brain.
Changes in gut microbiota may occur due to highly processed diets, which are high in sugar and fat, stress and chemical substances. An imbalance of our gut microbiota decreases levels of norepinephrine and dopamine in the brain. Tryptophan cannot be synthesised efficiently and this then affects serotonin and melatonin production (1).
Diets high in refined fat, sugar and low-fibre carbohydrates, result in systemic inflammation as harmful bacteria and foreign antigens seep through the damaged lining of the gut epithelial wall, into the bloodstream and eventually to the brain (2).
Comorbidity behaviours to anxiety are often binge drinking and other substance abuse. This causes more alterations to gut microbiota, further depleting the organic neurotransmitters and final, cortisol levels increase in this stressful environment further contributing to systemic inflammation.
Foods that promote Healthy Gut Microbiota
The International Society for Nutritional Psychiatric Research (ISNPR) exist to grow in the field of nutritional psychiatry. They have produced many papers on a range of topics associated with gut microbiota health and the effects on depression and other psychiatric disorders. Research has found that the following foods provide antioxidant properties and positively influence intestinal microbiota including an increase of lactobacilli and bifidobacteria and ultimately improving brain health and depression:
- Fibre-rich carbohydrates
- Whole fruits and vegetables
- Green Tea
- Fermented rice
- Foods rich in Omega 3 Fatty acids
Magnesium and Zinc also assist in preserving the diversity of gut microbiota and decreasing the systemic burden. In fact, research consistently shows that low levels of zinc in the diet is linked to long-term depression (2).
In 2009, research by Sanchez-Villegas et al., revealed after a 10-year follow-up of individuals involved in a seminal study, that the Mediterranean-style diet, had reduced the risk of depression (3). In 2010, an Australian study determined that a diet including vegetables, fruit, beef, lamb, fish and wholegrain foods, had a positive effect on reducing the risk of anxiety disorders and major depressive disorder (4).
Exercise has also been well documented in reducing the risk of, as well as improving the coping of those suffering depression and anxiety. In relation to the diversity of gut microbiota and exercise is closely related to diet. As mentioned above, a processed diet high in fats and refined carbohydrates with no physical activity levels can lead to obesity, causing systemic inflammation and changes in the diversity of gut microbiota.
However, excessive exercise combined with restrictive dieting, where many food groups are eliminated, can also have a negative effect of the diversity of gut microbiota. A study by Clarke et al., concludes that exercise can be beneficial in improving gut health but this is a complicated relationship affected by dietary extremes (5). Excessive exercise is often characterised by anxiety if exercise sessions are missed and this stress also affects gut health.
So as you can see, losing weight, controlling your dietary intake and ensuring exercise is done healthily, is critically important in maintaining the most appropriate balance between life, exercise and food when it comes to supporting mental health.
This article is just a brief introduction and summary of a few articles on the growing research on this topic. A balance of exercise and a diverse diet, low in processed foods and low in harmful behaviours often used to manage stress, can positively impact the diversity of systemic inflammation and gut microbiota.
Similarly, chronic physical illness induced by obesity and diabetes may also play a critical role in impacting gut microbiota.
For more information, additional research can be found at: http://www.isnpr.org
And as always with issues of this magnitude, medical consultation and supervision are highly recommended.
1. Evrensel, A., & Ceylan, M. E. (2015). The gut-brain axis: the missing link in depression. Clinical Psychopharmacology and Neuroscience, 13(3), 239.
2. Bested, A. C., Logan, A. C., & Selhub, E. M. (2013). Intestinal microbiota, probiotics and mental health: from Metchnikoff to modern advances: Part II–contemporary contextual research. Gut pathogens, 5(1), 3.
3. 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: 1090-1098.
4. Jacka FN, Pasco JA, Mykletun A, et al. Association of Western and traditional diets with depression and anxiety in women. Am J Psychiatry 2010; 167: 305-311.
5. Clarke, S. F., Murphy, E. F., O'sullivan, O., Lucey, A. J., Humphreys, M., Hogan, A., ... & Kerins, D. M. (2014). Exercise and associated dietary extremes impact on gut microbial diversity. Gut, gutjnl-2013.