Raiyan Talukder

Background: Depression is one of the most common mood disorders in the world, characterized by at least 2 weeks of depressed mood, anhedonia, loss of interest, and other symptoms.¹ Unfortunately, depression is a growing issue, affecting over 280 million people worldwide with some communities observing a large uptick in incidence after the COVID-19 pandemic.^1,2Since depression is a highly complicated disease state, novel therapies are needed. Recent trends in depression research have involved the enteric nervous system, namely the gut microbiome, an amalgam of bacteria, fungi, viruses, and other microbes within the gastrointestinal system.³ Currently, clinicians and researchers report that lifestyle changes can improve depressive symptoms in some patients.⁴ However, more research is needed for exact guidelines: many basic science studies aim to understand the biomolecular pathway of depression, while observational experiments view depression scores after a treatment. This literature review attempts to bridge the biological changes of the gut microbiome to mood improvements from diet modifications to ultimately expand the understanding of diet as a potential therapy in the treatment of depression.

Methods: The following search phrase was used in the PubMed database: ((depression) OR (major depressive disorder)) AND (gut microbiome).

Results: An experiment involving fecal microbiota transplants from human donors with depression to rats found that the subjects gained depressive-like symptoms and changes in their gut microbiome.⁵ While the link between the gut microbiome and depression was being established, a different research group explored its biomolecular role. They realized that serotonin, a major neurotransmitter implicated in depression, is synthesized in the gut and found patients with long-term depression had a similar change in populations of certain taxa.⁶ To modulate this aberrant microbiome, a clinical trial treated patients with probiotics and found that their serotonin levels and depression scores improved.⁷ Finally, a 2024 study observed that the Mediterranean diet improved depression symptoms in young males, likely due to improving the microenvironment to favor certain species.⁸

Conclusion: Depression affects many people worldwide, and its prevalence is increasing. New therapeutics are necessary for better depression management and nutritional psychiatry is attempting to find various foods to optimize the gut microbiome. While many advancements have been made on the bench, further research is needed to identify beneficial and detrimental foods before clinicians can draft individual diet plans to help patients at the bedside. In short, diet is a promising therapeutic for the treatment of depression and may help many patients improve their symptoms.

Works Cited:

1. Depressive disorder (Depression). Accessed April 29, 2024. https://www.who.int/news-room/fact-sheets/detail/depression Inc G. U. S. Depression rates reach new highs. Gallup.com. Published May 17, 2023. Accessed April 29, 2024. https://news.gallup.com/poll/505745/depression-rates-reach-new-highs.aspx
2. Limbana T, Khan F, Eskander N. Gut Microbiome and Depression: How Microbes Affect the Way We Think. Cureus. Aug 23 2020;12(8):e9966. doi:10.7759/cureus.9966
3. Abdijadid. ZMSPPS. Antidepressants. StatPearls Publishing; 2023.
4. Knudsen JK, Michaelsen TY, Bundgaard-Nielsen C, et al. Faecal microbiota transplantation from patients with depression or healthy individuals into rats modulates mood-related behaviour. Sci Rep. Nov 8 2021;11(1):21869. doi:10.1038/s41598-021-01248-9
5. Liu L, Wang H, Chen X, Zhang Y, Zhang H, Xie P. Gut microbiota and its metabolites in depression: from pathogenesis to treatment. eBioMedicine. 2023;90doi:10.1016/j.ebiom.2023.104527
6. Kazemi A, Noorbala AA, Azam K, Eskandari MH, Djafarian K. Effect of probiotic and prebiotic vs placebo on psychological outcomes in patients with major depressive disorder: A randomized clinical trial. Clin Nutr. Apr 2019;38(2):522-528. doi:10.1016/j.clnu.2018.04.010
7. Bayes J, Schloss J, Sibbritt D. The use of diet for preventing and treating depression in young men: current evidence and existing challenges. Br J Nutr. Jan 28 2024;131(2):214-218. doi:10.1017/s000711452300168x