A Gut Feeling: The Relationship Between Your Microbiome and Mental State

Why have you been so sad eating dining hall food every day? It’s not just the lack of seasoning; the diversity in your gut bacteria might be as slim as your dinner options. The gut-brain axis is a two-way communication pathway facilitated by the vagus nerve which allows for the brain and gastrointestinal system to exchange physiological and psychological activity occurring in the body (Wang et al. 2025). It is widely understood that a nutritional diet aids an individual’s physical health, but it is not often correlated with mental health benefits directly. However, building a diverse gut microbiome through a rich variety of foods physically impacts the bacteria in the intestines by increasing the number of beneficial bacteria and repressing harmful ones (Dinan 2023).

Beneficial bacteria refer to specific species of organisms in the microbiome capable of synthesizing tryptophan: an essential amino acid in the process of serotonin synthesis in the brain. Tryptophan produced by gut bacteria such as Escherichia coli travels to the brain through the gut-brain axis, allowing for the synthesis of serotonin (Martinez-Gomez et al. 2012). Tryptophan is one of the nine amino acids humans cannot independently synthesize, and with the assistance of gut bacteria the synthesis of serotonin is in greater abundance.

 Similarly, harmful bacteria are microorganisms in the intestines hypothesized to have a direct correlation to clinical depression. A 2024 study comparing the stool samples of individuals with diagnosed depression and healthy individuals found that the Firmicutes phylum of bacteria was found in every individual of the first group, and in none of the control group (Arbabi et al. 2024). This does not suggest that the bacteria are solely responsible for the depression diagnosis but instead draws a correlation between mental health and the species of bacteria living in the gut microbiome.

The gut microbiome is an ecosystem that thrives on a high level of diversity. By eating a variety of probiotics, prebiotics, and dietary fiber, humans can aid their gut microbiome by creating favourable conditions for beneficial bacteria growth. If the gut microbiome is a diverse and stable system, it can persist through infection of a harmful bacterial species or a few bad meals (Ebel et al. 2026). However, frequent consumption of artificial sweeteners and preservatives can supress the growth of good bacteria significantly (Xiong et al. 2023).

Overall, a nutritional diet full of natural, whole foods significantly impacts one’s mental health by physically nourishing the gut microbiome which works in our favour when it eats sufficiently. By feeding good bacteria and helping it multiply, we reap the benefits of a greater increase in serotonin, and potential natural treatments for mental disorders.

References

Ebel, Eric R., et al. “Gut Microbiomes of Tribal Communities in India Vary with Dairy and Grain Consumption.” Gut Microbes 18, no. 1 (2026): 2694242. https://doi.org/10.1080/19490976.2026.2694242.

Arbabi, Shapoury, Haghi, Zeighami, and Pirzeh. “Investigating the Bacterial Profiles of Lactobacillus, Bifidobacterium, Actinobacteria, Fusobacterium, Firmicutes, and Bacteroides in Stool Samples from Patients with Severe Depression and Healthy Individuals.” Psychoneuroendocrinology 170 (December 2024): 107090. https://doi.org/10.1016/j.psyneuen.2024.107090.

Wang, Duan, Du, Zhu, Wang, Hu, and Sun. “Vagus Nerve and Gut-Brain Communication.” The Neuroscientist 31, no. 3 (June 2025): 262–78. https://doi.org/10.1177/10738584241259702.

Xiong, Li, Cheng, Zhou, Wu, Huang, Saimaiti, Yang, Gan, and Li. “The Role of Gut Microbiota in Anxiety, Depression, and Other Mental Disorders as Well as the Protective Effects of Dietary Components.” Nutrients 15, no. 14 (July 2023): 3258. https://doi.org/10.3390/nu15143258.

Dinan. “Key Role of Nutrition in Mental Health.” Irish Journal of Psychological Medicine 43, no. 2 (June 2026): 161–62. https://doi.org/10.1017/ipm.2026.10180.

Martinez-Gomez, Karla, Noemi Flores, Hector M. Castaneda, et al. “New Insights into Escherichia coli Metabolism: Carbon Scavenging, Acetate Metabolism and Carbon Recycling Responses during Growth on Glycerol.” Microbial Cell Factories 11, no. 1 (2012): 46. https://doi.org/10.1186/1475-2859-11-46.