The intestinal microbiome, also called intestinal flora, is all the microorganisms (bacteria, viruses, fungi, etc.) that live in our intestine1. It plays an essential role in many physiological processes, including digestion, immunity and mental health1,2.

In recent years, researchers have discovered that certain metabolites produced by the gut microbiome can have a significant impact on mental health3. These metabolites are chemical substances that result from the digestion of food by gut bacteria2, 3.

Mechanisms of action

The mechanisms by which gut microbiome metabolites may influence mental health are still poorly understood. However, researchers have identified several potential mechanisms, including:

  • Inflammation: Inflammation is a normal physiological process that is triggered by the immune system to fight infections and injuries4. However, chronic inflammation can have detrimental effects on mental health5. Some gut bacteria can produce inflammatory substances, while others can help reduce inflammation 2,5.
  • The gut-brain axis: The gut-brain axis is a bidirectional communication pathway between the gut and the brain6. It is involved in the regulation of many functions, including digestion, immunity and mood2. The gut microbiome can influence the gut-brain axis by producing neurotransmitters and other chemicals that act on the brain3.
  • Metabolite production: As mentioned previously, the gut microbiome produces a variety of metabolites that can impact mental health. Some of these metabolites have anti-inflammatory, neuroprotective or anxiolytic properties7,8.

Examples of metabolites

Here are some examples of gut microbiome metabolites that are important for mental health:

  • Butyric acid is a short-chain fatty acid that is produced by the fermentation of dietary fiber 9. It has anti-inflammatory and neuroprotective properties10. Studies have shown that butyric acid can reduce symptoms of depression and anxiety9, 11.
  • Tryptophan is an essential amino acid that is used by the body to produce serotonin, a neurotransmitter that plays an important role in mood and sleep12,13. Some intestinal bacteria produce tryptophan, and others are still responsible to produce submetabolites that have a role in intestinal and neural homeostasis12, 13, 14.
  • Omega-3 fatty acids are essential fatty acids that are important for brain health15. Studies have shown that people with high levels of omega-3 fatty acids in their blood have a lower risk of developing mental disorders such as depression and anxiety16.

Innovations

The gut microbiome is now at the heart of groundbreaking innovations that are redefining our understanding of mental health.

New therapeutic targets & new treatments

Recent research has identified several mechanisms by which the gut microbiome may influence mental health. For example, bacterial dysbiosis, i.e., an imbalance in the gut microbiome, can lead to systemic and central nervous system inflammation17. This inflammation can contribute to a variety of mental disorders, such as depression, anxiety, and schizophrenia18, 19. These findings have opened the door to new therapeutic targets for mental disorders: preliminary studies have shown that treatments targeting gut inflammation can improve symptoms of depression and anxiety20.

Innovative nutritional tools

In addition to drug treatments, innovative nutritional tools can also be used to improve gut microbiome health and, therefore, mental health. For example, probiotics, live microorganisms that benefit gut health, have been shown to reduce symptoms of depression and anxiety21, 22.

Towards personalized medicine

Conclusion

There is growing evidence that the gut microbiome has a significant influence on mental health. By targeting the uniqueness of everyone’s microbiome, it is possible to improve mental health and contribute to overall well-being. Attention to microbiome details and personalized nutritional solutions is fast becoming a central part of the therapeutic approach, highlighting the importance of personalization in promoting mental health in the future.

References

  1. Shreiner, Andrew B., John Y. Kao, and Vincent B. Young. “The gut microbiome in health and in disease.” Current opinion in gastroenterology 31.1 (2015): 69.
  2. Galland, Leo. “The gut microbiome and the brain.” Journal of medicinal food 17.12 (2014): 1261-1272.
  3. Spichak, Simon, et al. “Mining microbes for mental health: Determining the role of microbial metabolic pathways in human brain health and disease.” Neuroscience & Biobehavioral Reviews 125 (2021): 698-761.
  4. Antonelli, Maria, and Irving Kushner. “It’s time to redefine inflammation.” The FASEB Journal 31.5 (2017): 1787-1791.
  5. Carlessi, Anelise S., et al. “Gut microbiota–brain axis in depression: The role of neuroinflammation.” European Journal of Neuroscience 53.1 (2021): 222-235.
  6. Carabotti, Marilia, et al. “The gut-brain axis: interactions between enteric microbiota, central and enteric nervous systems.” Annals of gastroenterology: quarterly publication of the Hellenic Society of Gastroenterology 28.2 (2015): 203.
  7. Rutsch, Andrina, Johan B. Kantsjö, and Francesca Ronchi. “The gut-brain axis: how microbiota and host inflammasome influence brain physiology and pathology.” Frontiers in Immunology 11 (2020):604179.
  8. Liaqat, Humna, Amna Parveen, and Sun Yeou Kim. “Neuroprotective Natural Products’ Regulatory Effects on Depression via Gut–Brain Axis Targeting Tryptophan.” Nutrients 14.16 (2022): 3270.
  9. Bourassa, Megan W., et al. “Butyrate, neuroepigenetics and the gut microbiome: can a high fiber diet improve brain health?.” Neuroscience letters 625 (2016): 56-63.
  10. Alpino, Gabriela de Cássia Ávila, et al. “Beneficial effects of butyrate on brain functions: A view of epigenetic.” Critical Reviews in Food Science and Nutrition (2022): 1-10.
  11. Suda, Kazunori, and Kazunori Matsuda. “How microbes affect depression: underlying mechanisms via the Gut–brain axis and the modulating role of probiotics.” International journal of molecular sciences 23.3 (2022): 1172.
  12. O’Mahony, Siobhain M., et al. “Serotonin, tryptophan metabolism and the brain-gut-microbiome axis.” Behavioural brain research 277 (2015): 32-48.
  13. Roth, William, et al. “Tryptophan metabolism and gut-brain homeostasis.” International journal of molecular sciences 22.6 (2021): 2973.
  14. Bosi, Annalisa, et al. “Tryptophan metabolites along the microbiota-gut-brain axis: an interkingdom communication system influencing the gut in health and disease.” International Journal of Tryptophan Research 13 (2020): 1178646920928984.
  15. Lange, Klaus W. “Omega-3 fatty acids and mental health.” Global Health Journal 4.1 (2020): 18-30.
  16. Antao, Helena Sofia, et al. “Omega-3 index as risk factor in psychiatric diseases: a narrative review.” Frontiers in Psychiatry 14 (2023).
  17. Almeida, Cátia, et al. “Influence of gut microbiota dysbiosis on brain function: a systematic review.” Porto biomedical journal 5.2 (2020).
  18. Rogers, G. B., et al. “From gut dysbiosis to altered brain function and mental illness: mechanisms and pathways.” Molecular psychiatry 21.6 (2016): 738-748.
  19. Nemani, Katlyn, et al. “Schizophrenia and the gut–brain axis.” Progress in Neuro-Psychopharmacology and Biological Psychiatry 56 (2015): 155-160.
  20. Moulton, Calum D., et al. “Depressive symptoms in inflammatory bowel disease: an extraintestinal manifestation of inflammation?.” Clinical & Experimental Immunology 197.3 (2019): 308-318.