The topic today is a pretty cool example of gene-environment interactions. As these GEITP pages have discussed before, the bacteria in our gut (comprising each individual’s ‘MICROBIOME’) account for ~92% of all “our” DNA (i.e. just 8% of DNA is ‘our own’). Moreover, it is well known that diet and geographical environment are two principal determinants of microbiome structure and function. Rural indigenous populations have been found to harbor substantial biodiversity in their gut microbiomes — which sometimes even include novel microbial taxa (each ‘taxon’ is an evolutionary group of one or more populations of an organism, categorized by taxonomists to form a unit) not found in industrialized populations. This loss of indigenous microbes or ‘‘disappearing microbiota’’ (in migrants now living on a different country) may be important in explaining the rise of chronic diseases in the modern world. Despite the frequent migration of people across national borders in an increasingly interconnected world, little is known about how human migration affects one’s individual microbiome.
The United States hosts the largest number of immigrants in the world (49.8 million; 19% of the world’s total immigrants and ~21% of the U.S. population). Epidemiological evidence shows that residency in the US increases risk of obesity and other chronic diseases among immigrants (compared with individuals of the same ethnicity that continue to reside in their country of birth); indeed, some groups exhibit as much as a 4-fold increase in obesity after 15 years at their new location. In addition to Latinos migrating northward, Southeast Asian refugees display the highest average increases in body mass index (BMI) after relocation to the US. The Hmong, a minority ethnic group from China (i.e. SE Asia), make up the largest refugee group in Minnesota; the Karen, an ethnic minority from Burma, have been arriving in large numbers in more recent years. Overweight status and obesity rates are highest among Hmong and Karen, compared with other Asian ethnic groups in Minnesota. Changing to Western diet, previous history of malnutrition, and physical inactivity — have been suggested as contributing factors.
Authors [see attached article] analyzed stool, diet, and anthropometrics from 514 Hmong and Karen individuals living in Thailand versus the US, including first- and second-generation immigrants and 19 Karen individuals sampled before and after immigration, as well as from 36 US-born European-American individuals. By means of DNA sequencing of gut bacteria, authors found that migration from a non-Western country to the US is associated with immediate loss of gut microbiome diversity and function in which US-associated strains and functions displace native strains and functions. These effects were found to increase, as a function of the duration of US residence, and these effects are compounded by obesity and across generations.
Cell 2o18; 175: 962–972
COMMENT: Dan, I believe that “duration of US residence,” especially for children, would translate directly into “likelihood of (probably unnecessary) trearment with oral antibiotics in this country” — which will devastate your gut microbiome. The result in these kids would mean much less diverse population of microbiota.