Written by Mariam Karma | Edited by Olivia Cooper
Photo by Kindel Media
Does the phrase “you are what you eat” sound familiar [1]? The gut microbiota contains trillions of microorganisms that live in the intestines; even just the number of bacterial cells within the gut microbiota outnumber human cells in the entire body. In a healthy gut, a diverse array of microorganisms extracts nutrients from a variety of foods [2] [3]. The diversity of microorganisms in the gut microbiota is also linked to mood. A 2019 study of 1,045 participants in Belgium showed varying gut microbiota composition between healthy participants and those diagnosed with depression. Those diagnosed with depression lacked species of bacteria associated with mental well-being [3]. Because bacteria constitute most of the gut microbiota, and bacterial diversity in the gut does correlate with a person’s mental state.
Beneficial bacteria in the gut are associated with one’s level of contentment. They can use tryptophan, a chemical extracted from foods like turkey and chia seeds, to produce serotonin. Serotonin is a brain chemical associated with happiness; higher serotonin levels decrease feelings of depression. These ”good” types of bacteria also use tyrosine, a chemical found in foods like almonds and lentils, to produce dopamine. Dopamine is a chemical associated with motivation; greater dopamine presence in the brain increases feelings of motivation in individuals with depression [1]. Such chemicals travel from the gut to the brain through the vagus nerve [4]. Although good bacteria produce chemicals that help decrease depressive symptoms, their function is undermined if they are outnumbered by different types of “bad” bacteria.
Detrimental bacteria in the gut microbiota are associated with depressed mental states. These “bad” bacteria digest fatty foods like pizza and ice cream, which do not contain nutritious chemicals required for mental well-being [1]. Instead, the metabolism produces inflammatory signals that leave the brain vulnerable to depression—one such way being decreasing the production of nerve cells in brain regions linked to depressive states [4] [5]. Periods of pronounced stress also increase depressive symptoms through the release of a hormone called cortisol, which inhibits the body’s stress response system and sparks the same cycle of production of inflammatory signals by bad bacteria [6]. Fortunately, there are ways to increase diversity in the gut microbiota so that the bad bacteria do not outnumber the good bacteria and trigger depression.
Fecal Microbiota Transplantation (FMT) is a procedure that increases gut diversity, a feat usually attributed to probiotics and prebiotics. FMT involves transplanting feces containing a diverse collection of bacteria to individuals lacking bacterial diversity. The newly introduced bacteria outnumber the existing bad bacteria in the gut and produce the chemicals needed for mental well-being. FMT seems to be more beneficial for gut diversity than consuming probiotics like yogurt and pickles, which are foods containing live colonies of beneficial bacteria [4] [6]. Unlike FMT, probiotics are limited to specific types of bacteria that may not fit a certain gut’s diversity needs. In addition, FMT has a more long-term impact because the bacteria it transports are not at risk of destruction by stomach acid, which is a common problem faced when ingesting probiotics [2]. However, if FMT sounds discomforting, then consuming probiotics and prebiotics, which are foods like garlic and bananas that contain fibers promoting the growth of good bacteria [4], can help decrease inflammatory signals linked to depression and improve gut health [6].
References:
[1] “Your Gut Microbiome: The Most Important Organ You’ve Never Heard Of.” Youtube, uploaded by TEDx Talks, 12 Dec. 2019, www.youtube.com/watch?v=B9RruLkAUm8-. Accessed 05 April 2022.
[2] Hasan, N., Yang, H. (2019). Factors affecting the composition of the gut microbiota, and its modulation. PeerJ, 7:e7502.
[3] Butler, M. I., Mörkl, S., Sandhu, K. V., Cryan, J. F., Dinan, T. G. (2019). The gut microbiome and mental health: What should we tell our patients?: Le microbiote intestinal et la santé mentale : Que devrions-nous dire à nos patients? The Canadian Journal of Psychiatry, 64:747–760.
[4] “How Your Gut Bacteria Controls Your Mood.” YouTube, uploaded by Dr. Tracey Marks, 2 June 2021, www.youtube.com/watch?v=5h3Y4iNcN8g&t=145s. Accessed 05 April 2022.
[6] Clapp, M., Aurora, N., Herrera, L., Bhatia, M., Wilen, E., Wakefield, S. (2017). Gut microbiota’s effect on Mental Health: The gut-brain axis. Clinics and Practice, 7:987.