What is the Gut Microbiome?

By: Tana Mardian

When we think about bacteria, our minds are often flooded with  negative thoughts. We remember the pounding headache from a sinus infection or that gross cut that got infected. We often overlook the “good” bacteria that lives in and around us all the time, such as the bacteria that lives in our digestive system. Harvard’s T.H. Chan School of Public Health compares the gut microbiome to a busy city on a weekday morning, with sidewalks full of people going to a bunch of different places at once. They explain that our gut microbiome isn’t much different, bustling with bacteria, fungi, parasites, and viruses, making up the trillions of microorganisms that live in us (mostly in the small and large intestines). In a healthy individual, all of these microorganisms work together to have a functional and efficient digestive system (Harvard T.H. Chan School of Public Health). 

While we might not always think about the little “bugs” in our gut, the microbiome is a critical player in metabolism, protection against pathogens, and the immune system. As such, these microorganisms have profound effects on our physiology in both healthy and disease states, and while the field is still growing, researchers recently have been investigating the role of the microbiome in certain conditions (Shreiner et al., 2016). 

The high prevalence of obesity in the United States has initiated more research about the importance of the microbiome. Evidence suggests that having a diverse microbiome can be preventative in long-term weight gain, and a negative correlation exists between BMI and gut microbiota diversity. In other words, a high BMI is associated with a lower variety of gut microbiota, and this is an important finding due to the significance of diversity in gut bacteria (Aoun et al., 2020). Having a diverse microbiome is typically advantageous to health; it is associated with the production of beneficial metabolites, such as anti-inflammatory short chain fatty acids, and decreased development of inflammatory mediators (Laitinen & Mokkala, 2019). Additionally, those with obesity tend to have a higher ratio of Firmicutes to Bacteroidetes, and this ratio seems to be important in maintaining a healthy weight. Research demonstrates that there is a correlation between higher Bacteroidetes and weight loss as well as  between Firmicutes and progression of obesity. It’s essential to note that there are ways to improve gut microbial diversity, including taking probiotics and prebiotics. Studies have demonstrated that probiotics can reduce BMI and visceral fat, preventing increases in body weight and fat. Prebiotics enhance metabolic outcomes and the gut’s barrier to pathogens, as well as reduce food intake. While probiotics and prebiotics are two ways to help with gut bacteria health, dietary intervention, exercise, and other medications have also been found to  improve gut health in those with obesity (Aoun et al., 2020).

Another emerging area of research is looking into the relationship between the gut microbiome and mental illness,  most notably the gut’s effects on depression and anxiety. The gut microbiota acts as a critical mediator for biochemical signaling that occurs between the gastrointestinal tract and the central nervous system, and this is known as the gut-brain axis. With this in mind, researchers looked further into the connection between the microbiome and the brain (Durack & Lynch, 2019). Some studies have taken specific probiotics or antibiotics to manipulate the gut microbiome and have found that they can elicit behaviors similar to those seen in someone with depression. There is also evidence to suggest that prenatal stress and stress early on in life can change the gut microbiota. These harmful changes may happen during crucial neurodevelopmental periods and can even continue into adulthood. The gut microbiome can also influence serotonin and tryptophan (sertonin’s precursor), adjust our response to stress, and regulate cognition (Dash et al., 2015). The significance of the gut microbiome in mental health is apparent, and researchers continue to investigate the relationship between the two.

As such a complex and emerging topic, there is still much room in the literature to explore the significance of the gut microbiome in our everyday health. There is a growing list of disorders that seem to have a relationship with the microbiota in our digestive system, such as autism spectrum disorders, schizophrenia, Parkinson’s disease, multiple sclerosis, and bipolar mood disorders (Cullen et al., 2020). This is clearly a growing field with far-reaching discoveries. Through these studies, researchers may be able to get a deeper understanding of the gut microbiome and hopefully figure out even more ways to improve our health.

Reference List

Aoun, Antoine, Fatima Darwish, and Natacha Hamod. “The Influence of the Gut Microbiome on Obesity in Adults and the Role of Probiotics, Prebiotics, and Synbiotics for Weight Loss.” Preventive Nutrition and Food Science 25, no. 2 (June 30, 2020): 113–23. https://doi.org/10.3746/pnf.2020.25.2.113.

CDC. “Obesity Is a Common, Serious, and Costly Disease.” Centers for Disease Control and Prevention, November 12, 2021. https://www.cdc.gov/obesity/data/adult.html.

Cullen, Chad M., Kawalpreet K. Aneja, Sinem Beyhan, Clara E. Cho, Stephen Woloszynek, Matteo Convertino, Sophie J. McCoy, et al. “Emerging Priorities for Microbiome Research.” Frontiers in Microbiology 11 (2020). https://www.frontiersin.org/article/10.3389/fmicb.2020.00136.

Dash, Sarah, Gerard Clarke, Michael Berk, and Felice N. Jacka. “The Gut Microbiome and Diet in Psychiatry: Focus on Depression.” Current Opinion in Psychiatry 28, no. 1 (January 2015): 1–6. https://doi.org/10.1097/YCO.0000000000000117.

Laitinen, Kirsi, and Kati Mokkala. “Overall Dietary Quality Relates to Gut Microbiota Diversity and Abundance.” International Journal of Molecular Sciences 20, no. 8 (January 2019): 1835. https://doi.org/10.3390/ijms20081835.

Shreiner, Andrew B., John Y. Kao, and Vincent B. Young. “The Gut Microbiome in Health and in Disease.” Current Opinion in Gastroenterology 31, no. 1 (January 2015): 69–75. https://doi.org/10.1097/MOG.0000000000000139.

Harvard T.H. Chan School of Public Health: The Nutrition Source. “The Microbiome,” August 16, 2017. https://www.hsph.harvard.edu/nutritionsource/microbiome/.