Research on the human microbiome is revolutionizing the medical field and health as we know it. Microbial populations living in and on our bodies have unique genetic contributions to our metabolism, incidence of disease, aging, and behavior. The study of the human microbiome is opening the doors to new therapeutic approaches and helping us better understand the role of diet in health and disease.
The Human Microbiome
The human body is inhabited by trillions of microorganisms that form a type of “microbial suit” that we wear for the duration of our lives (2). As it turns out, we are composed mostly of microbial cells and are only about 43% human cells. When comparing the genetic contributions of microbes to human cells, ~ 1% of genes come from the human genome and the rest comes from microbes (3). This helps us better understand the deep influence that microbial communities have on our health.
The human microbiome refers to the collective genetic contribution of all microbes that inhabit the human body. It is to be distinguished from the human microbiota, which refers collectively to all microbial communities living in and on our bodies. The microbiome includes genes from bacteria, viruses, fungi, and other microorganisms that inhabit our bodies (1). Genetic contributions from these microorganisms have deep effects on our health and how our own genes are expressed.
Microbial populations on the human body can differ greatly from one part of the body to another. Microbes living on different parts of our skin, like our hands vs our face vs our armpits, are unique to their particular selective environments. The same can be said for microbial environments living inside the body, bacteria from our oral cavity differ greatly from bacteria in our colon.
Microbial communities can be studied to better understand their contributions to their environments and the environments themselves (our bodies!). Microbial communities on the skin, for example, can be studied to better understand body odor and its role in attracting mosquitos and human mates (4).
The gut is a major focus in microbiome research due to its impact on human physiology and health. The gut microbiota is very diverse and variable compared to other parts of the body and has a unique effect on our immune system and even our brain.
According to Dr. Robert Knight, co-founder of the American Gut Project, animal studies on the gut microbiota involving fecal transplants have revealed fascinating connections between the gut microbiota and physiology. Studies on obesity, for example, revealed that fecal transplants from obese mice to germ-free mice made the recipients more prone to obesity (3). Fecal transplants from lean mice, on the other hand, led to a lean recipient. A similar dynamic has been seen in personality studies by Bercik et al. in the journal Gastroenterology, where germ-free mice receiving a fecal transplant from a shy donor verses and bold donors show changes in personality resembling their donors. While nothing is definitive, these types of studies are definitely suggestive and reveal interesting dynamics between gut microbes and behavior.
Dietary Influence on the Gut
Diet is a major determinant of gut microbiota and health. It is important to support a healthy gut environment by eating plenty of fruits and vegetables which can serve as prebiotics to feed too healthy bacteria. Limiting the number of processed and highly refined foods is also good for promoting a diverse microbial environment in the gut and a positive effect on overall health.
- Shreiner, A. B., Kao, J. Y., & Young, V. B. (2015, January). The gut microbiome in health and in disease. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/25394236
- UCTV, U. O. (2019, December 23). VIDEO: The Human Microbiome: A New Frontier in Health. Retrieved from https://www.uctv.tv/shows/35240
- Follow Your Gut: Microbiomes and Aging with Rob Knight … (n.d.). Retrieved from https://www.youtube.com/watch?v=2iKHMyWzclM
- The Human Microbiome – Introduction to Microbes and the Human Microbiome. (n.d.). Retrieved from https://www.coursera.org/lecture/microbiome/the-human-microbiome-EFtJY