Review of: Vangay P, et al. 2018. US Immigration Westernizes the Human Gut Microbiome. Cell. 175:962-972.
The gut microbiome has become a hot topic in the scientific community, and it is hoped that understanding the symbiotic relationship between bacteria and humans will help elucidate the role of bacteria in gastrointestinal diseases. The diversity of the species of bacteria in the gut depends on both diet and the environment (De Filippo et al., Proc. Natl. Acad. Sci., 2010) and therefore, differs between human populations. For example, it has been shown that non-westernized populations have a much higher diversity of bacteria (Clemente et al., Science, 2015) and contain novel microbial taxa (Obregon-Tito et al., Nature Comm., 2015) compared to westernized populations. While studies have determined a difference in microbiota between populations, exactly how different gut microbiota adapt to a changing environment remains to be elucidated. To study the short-term and long-term effects of both diet and the environment on the gut microbiome population, Vangay et al. measured the gut microbiomes and dietary intake of Hmong and Karen immigrants relocating to the United States (Vangay et al., Cell, 2018). Vangay et al. conclude that these immigrants lose gut microbiome diversity as well as bacteria specific for degrading plant fibers (Vangay et al.).
Vangay et al., highlight two bacterial groups, Prevotella spp. and Bacterioides spp. Prevotella are Gram-negative bacteria that while typically absent in European populations, make up approximately 53% of the gut bacteria in the people of Burkina Faso, a non-westernized country (Wu et al., Science, 2011). Bacterioides are Gram-negative, obligate anaerobic bacteria, meaning they thrive in very low oxygen environments. The presence or absence of these two species depends on the host’s diet. Prevotella have been found to be predominantly in humans with a diet high in carbohydrates, especially fiber, whereas Bacterioides are found predominantly in humans with a diet high in protein and animal fat. Interestingly, Vangay showed that Bacterioides displaced Prevotella in immigrants that relocated to the USA, indicative of diet changes altering the main composition of the gut microbiome.
“You are what you eat,” has long been the foundation of nutritional guidelines, and what you eat alters your body, both long term at a genetic level and immediately, at a more physiological level. Diet can have immediate effects on your body, beyond weight gain and weight loss; it also has immediate effects on your gut microbiome composition, as shown by Vangay et al. While the findings in this study provide direct insight into how the change of environment and diet can alter the ratio of Prevotella and Bacterioides, there are some limitations to this research finding. For example, the data were analyzed by comparing between individuals, and data were collected at different times. Therefore, the researchers could only compare ratios of bacterial species between individuals, not across the entire population. Interpreting the data based only on ratios does not allow the researcher to discern between changes in the total numbers of bacterial species and species replacing one another. Additionally, there are no quantitative data in this study regarding the individual’s exact diet. A follow-up study looking at the exact metabolic mechanisms underlying changes in bacterial species would be necessary to truly elucidate how different metabolites support different bacterial species.
Citations:
Clemente, J et al. (2015). The microbiome of uncontacted Amerindians. Microbial Ecology, 1(3). doi:10.1126/sciadv.1500183
De Filippo C et al. (2010). Impact of diet in shaping gut microbiota revealed by a comparative study in children from Europe and rural Africa. PNAS, 107 (33). doi: 10.1073/pnas.1005963107.
Obregon-Tito et al. (2015). Subsistence strategies in traditional societies distinguish gut microbiomes. Nature Communications, 6:6505. doi: 10.1038/ncomms7505.
Wu et al. (2011). Linking long-term dietary patterns with gut microbial enterotypes. Science, 334(6052):105-8. doi: 10.1126/science.1208344.