The Link Between Gut Microbiome and Mental Health

Could the gut microbiome hold the key to mental health?

Worldwide, millions suffer from psychiatric illness or mental health disorders. Depression, for example, affects an estimated 264 million people and is recognised by the World Health Organisation (WHO) as “a major contributor to the overall global burden of disease”. There are effective treatments for mental disorders but, as noted by the WHO, social support and access to health care and related services, is key. ¹

Amid growing scientific evidence of the link between the gut microbiome and the brain, scientists believe it may become possible to treat psychiatric illness via the gut-brain axis. ² In fact, scientists have identified the specific microbiota that influence neurons and the brain. They’re called ‘psychobiota’ – a term coined by John Cryan (a neuropharmacologist) and Ted Dinan (a psychiatrist). ³

What we do know about psychobiota is that they have a direct influence on our immune systems, managing inflammation. They secrete substances directly into the bloodstream, which carries them to the brain. These microbes also prompt cells in the gut lining to stimulate the vagus nerve (linked to the brain). Additionally, these microbes activate the endocrine cells in the gut, responsible for the production and secretion of hormones in the body.⁴

Research studies around the globe have made a number of additional pertinent findings relating to psychobiota. For example:

In studying the link between depression and the microbiome, researchers found a correlation between depression and deficiencies in specific microbes.^{5 & 6 & 7}
Autism studies find that children with the condition have a distinct gut microbiome when compared to children without the condition. Many of these children also appear to have symptoms of irritable bowel syndrome (IBS). Additionally, in animal studies, autism-like symptoms appear when certain microbes are absent. ⁸
Studies have found a link between the microbiome and anxiety or stress. ^{9 & 10} In one study, scientists found that rats treated with antibiotics suffered from exacerbated anxiety and high stress. ¹¹
Studies are establishing the link between the microbiome and mental illness, including schizophrenia, bipolar disorder and depression. ¹²

Even though, there is no definitive guideline for psychobiotic treatment as yet; there is a need for greater scientific evidence to support a dietary treatment approach. ¹³

As Kathrin Cohen Kadosh (PhD of the School of Psychology at the UK’s University of Surrey) and her colleagues have noted: “As a still relatively unexplored area, any real progress will require a systematic multidisciplinary research approach, which gives priority to specifying mechanisms in the human and animal models, providing causal understanding and addressing realistic outcomes. This is particularly critical in light of strong public and commercial interests that are presently outpacing research efforts”. ¹⁴

Acknowledging that the research community still has a long way to go in providing a comprehensive foundation for psychobiotic treatment guidelines, there are a number of nutritional tips that we can share with patients, to help them improve their gut health:

Eat more healthy fibre (prebiotics): One study showed that a diet rich in prebiotics (fibre-rich foods that healthy gut bacteria feed on, such as onions and berries) had positive results. Study participants who followed this diet reported lower stress levels in general (with stress tests showing healthier responses too). The composition of their gut biomes were shown to have changed, with larger volumes of healthy bacteria. ¹⁵
Eat more probiotic foods: This includes fermented foods such as sauerkraut or kimchi, and probiotic yoghurt. Supplementing with a good quality probiotic is also wise, given the results of tests showing that these support psychobiotic function (promoting the release of happy hormones). ¹⁶

Sidebar – 11 prebiotic foods that boost healthy gut bacteria¹⁷
- Garlic
- Onion
- Leeks
- Asparagus
- Bananas
- Barley
- Oats
- Apples
- Cocoa
- Flaxseeds
- Wheat bran
Eat a Mediterranean diet: Rich in fresh vegetables, fruit, nuts and fish, eggs and olive oil, the Mediterranean diet is proving to be ideal for the promotion of a healthy gut. Additionally, studies are finding that patients who follow this diet report fewer symptoms of mental illness (depression, etc).¹⁸
Cut back on sugar: Sugar, it seems, is the favourite food of pathogenic bacteria. Likewise, scientists are finding a direct link between high sugar intake and rate of depression. ¹⁹
Eat more Omega 3s: Studies have found that healthy Omega-3 fatty acids (found in fish, nuts and plant oils) support microbiome health.
Avoid artificial sweeteners: Scientists have found a relationship between artificial sweeteners (such as aspartame) and increased stress hormone levels. consideration is now given to stevia and erythritol instead of artificial sweeteners. ¹⁸

^{1 Who.int. 2020. Depression. [online] Available at: <https://www.who.int/news-room/fact-sheets/detail/depression> [Accessed 10 February 2021].

. Misra, S. and Mohanty, D., 2017. Psychobiotics: A new approach for treating mental illness?. Critical Reviews in Food Science and Nutrition, 59(8), pp.1230-1236

3 Psychology Today. 2019. Can You Eat Yourself Happy?. [online] Available at: <https://www.psychologytoday.com/us/blog/mood-microbe/201908/can-you-eat-yourself-happy> [Accessed 7 May 2021].

4 Science, 2020. Meet the ‘psychobiome’: the gut bacteria that may alter how you think, feel, and act. [online] (6491). Available at: <https://www.sciencemag.org/news/2020/05/meet-psychobiome-gut-bacteria-may-alter-how-you-think-feel-and-act> [Accessed 9 April 2021].

5 Valles-Colomer, M., Falony, G., Darzi, Y., Tigchelaar, E., Wang, J., Tito, R., Schiweck, C., Kurilshikov, A., Joossens, M., Wijmenga, C., Claes, S., Van Oudenhove, L., Zhernakova, A., Vieira-Silva, S. and Raes, J., 2019. The neuroactive potential of the human gut microbiota in quality of life and depression. Nature Microbiology, 4(4), pp.623-632.

6 Stower, H., 2019. Depression linked to the microbiome. Nature Medicine, 25(3), pp.358-358.

7 Strandwitz, P., Kim, K., Terekhova, D., Liu, J., Sharma, A., Levering, J., McDonald, D., Dietrich, D., Ramadhar, T., Lekbua, A., Mroue, N., Liston, C., Stewart, E., Dubin, M., Zengler, K., Knight, R., Gilbert, J., Clardy, J. and Lewis, K., 2018. GABA-modulating bacteria of the human gut microbiota. Nature Microbiology, 4(3), pp.396-403.

8 Stower, H., 2019. Depression linked to the microbiome. Nature Medicine, 25(3), pp.358-358.

9 Foster, J., 2021. Is Anxiety Associated with the Gut Microbiota?. In: Microbes and the Mind. pp.68-73.

10 Bear, T., Dalziel, J., Coad, J., Roy, N., Butts, C. and Gopal, P., 2021. The Microbiome-Gut-Brain Axis and Resilience to Developing Anxiety or Depression under Stress. Microorganisms, 9(4), p.723.

11 Glover, M., Cohen, J., Singer, J., Sabbagh, M., Rainville, J., Hyland, M., Morrow, C., Weaver, C., Hodes, G., Kerman, I. and Clinton, S., 2021. Examining the Role of Microbiota in Emotional Behavior: Antibiotic Treatment Exacerbates Anxiety in High Anxiety-Prone Male Rats. Neuroscience, 459, pp.179-197.

12 Tzavellas, E., Logotheti, M. and Stefanis, N., 2021. The Gut Microbiome in Serious Mental Illnesses. Gut Microbiome-Related Diseases and Therapies, pp.243-263.

13 Berding, K., Vlckova, K., Marx, W., Schellekens, H., Stanton, C., Clarke, G., Jacka, F., Dinan, T. and Cryan, J., 2021. Diet and the Microbiota–Gut–Brain Axis: Sowing the Seeds of Good Mental Health. Advances in Nutrition, [online] Available at: <https://pubmed.ncbi.nlm.nih.gov/33693453/> [Accessed 1 July 2021].

14 Healio.com. 2021. Researchers find limited evidence for psychobiotics as youth anxiety treatment. [online] Available at: <https://www.healio.com/news/psychiatry/20210625/researchers-find-limited-evidence-for-psychobiotics-as-youth-anxiety-treatment> [Accessed 5 July 2021].

15 Bbc.co.uk. 2020. BBC Two - Trust Me, I'm a Doctor, Series 9, Episode 2 - Can your food change your mood?. [online] Available at: <https://www.bbc.co.uk/programmes/articles/Qz3DW8TR0m8bSR8zWxQwwD/can-your-food-change-your-mood> [Accessed 4 April 2021].

16 FutureBridge. 2020. Psychobiotics – Emerging Next-Generation Probiotics for the Wellness of Mind & Gut - FutureBridge. [online] Available at: <https://www.futurebridge.com/industry/perspectives-food-nutrition/psychobiotics-emerging-next-generation-probiotics-for-the-wellness-of-mind-gut/> [Accessed 12 April 2021].

17 Westover, A. and Marangell, L., 2002. A cross-national relationship between sugar consumption and major depression?. Depression and Anxiety, 16(3), pp.118-120.

18 BBC Science Focus Magazine. 2021. Dr Michael Mosley: What to eat to beat stress and improve your mood. [online] Available at: <https://www.sciencefocus.com/comment/beat-stress-with-food/> [Accessed 1 July 2021].

19 Westover, A. and Marangell, L., 2002. A cross-national relationship between sugar consumption and major depression?. Depression and Anxiety, 16(3), pp.118-120.}