Meducated

Arya Singla, Walton High School (Marietta, GA)

It is commonly accepted that the human gut microbiome consists of over 1000 different microbial species¹. The human gut microbiome is a complex community of microorganisms like bacteria, viruses, fungi, etc. that live in the gastrointestinal tract. They help with a multitude of activities throughout the body, like, immune response, prevention of pathogen colonization, and breakdown of compounds during digestion. The composition of the gut microbiome largely affects the metabolic activity of an individual and can contribute to metabolic disorders.

Metabolic disorders are conditions that occur when the body’s normal process of converting food into energy is disrupted, often due to enzyme deficiencies or hormonal imbalances. The combination of both genetics, which determines the foundational composition of an individual’s
gut microbiome, and external factors such as diet, both illustrate the impact of how the metabolism of an individual can shape their health and daily life.

Genetic factors can partially determine the diversity and composition of the gut microbiome. A study on twins’ fecal samples revealed heritable patterns in specific microbial communities. A study, using monozygotic twins (identical twins), identified many heritable taxa by using taxonomic classification (a system that organizes living organisms into hierarchical categories based on shared characteristics)⁵. While it may have been due to similar habits or diet, the twins showed to have a greater similarity in composition rather than unrelated individuals or even siblings. The most heritable microbial species, by far, was the bacterial family of Christensenellaceae, which was also associated with individuals with a lower BMI⁵. This suggests a heritable effect of certain microbes, which help to play a role in regulating body weight.

In addition, a study in 2016 revealed that certain microbial taxa in the gut maintain their relative abundance over time. Further analysis of the participants highlighted the heritability of microbial taxa and functional modules linked to complex disease risk, with additional findings suggesting that environmental factors also play a significant role in shaping the gut microbiome ² ⁴. Hence, while genetics plays a crucial role in initially shaping the gut microbiome, environmental influences, particularly diet, significantly contribute to an individual’s metabolism and health as well. 

Environmental factors, for instance, diet, have been shown to have a link between individual microbiome composition and the metabolism of an individual, or the set of chemical reactions that take place to maintain homeostasis (balance within the body). Obesity was first linked to the gut microbiome in an experiment using mice that showed different ratios between the bacterial families Firmicutes and Bacteroidetes in obese and non-obese mice¹. Obesity typically results from an imbalance between energy intake and energy discharge. When analyzing fecal samples of humans, those with obesity seemed to have higher amounts of butyrate and propionate, both of which are short-chain fatty acids that help regulate and maintain homeostasis in the GI tract¹. The increased levels of butyrate and propionate in obese individuals help support the connection between obesity, gut microbiota, and metabolism³. Evidence shows a strong link between metabolism, immunity, and gut microbiota, suggesting that metabolic imbalances can lead to immune challenges and that disrupted gut microbiota balance may increase disease susceptibility. 

Both the genetic components of specific microbes, as well as the environmental components of the diet, contribute to the overall health and composition of the gut microbiota. Having a diverse microbial community is important to prevent an imbalance of microbes, which could be the solution to overcoming specific metabolic diseases. The gut microbiome is extraordinary, as while it partially may be predetermined by genetics, it can be manipulated by external factors and can change the health outcome of an individual entirely. 

References:

1. Bull, Matthew J., and Nigel T. Plummer. “Part 1: The Human Gut Microbiome in Health and Disease.” Integrative Medicine: A Clinician’s Journal, vol. 13, no. 6, 2014, p. 17.

2. Cahana, Inbal, and Fuad A. Iraqi. “Impact of Host Genetics on Gut Microbiome: Take‐home Lessons from Human and Mouse Studies.” Animal Models and Experimental Medicine, vol. 3, no. 3, 2020, pp. 229–236, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7529332/

3. de la Cuesta-Zuluaga, Jacobo, et al. “Higher Fecal Short-Chain Fatty Acid Levels Are Associated with Gut Microbiome Dysbiosis, Obesity, Hypertension and Cardiometabolic Disease Risk Factors.” Nutrients, vol. 11, no. 1, 2018, p. 51, 

4. Felicia N. New, et al. “Collective Effects of Human Genomic Variation on Microbiome Function.” Scientific Reports, vol. 12, no. 1, 2022, pp. 1–12, https://www.nature.com/articles/s41598-022-07632-3

5. Goodrich, Julia K., et al. “Human Genetics Shape the Gut Microbiome.” Cell, vol. 159, no. 4, 2014, pp. 789–799, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4255478/