Show me your gut flora, and i’ll tell you where you come from
A study published in the journal Cell reveals that migration from a non-Western country to the US could be associated with significant changes in the microbiota’s diversity and functions that could result in a predisposition to metabolic disorders.
International researchers reached this conclusion by studying over 510 women aged 18 to 78 belonging to the Hmong and Karen tribes, minorities from South East Asia whose migrants to the US are particularly affected by obesity. Scientific literature has previously shown that there is a link between excess weight and disruptions of microbiota. To understand the impact of migration on the gut microbiota, scientists analyzed the intestinal flora of women still living in Thailand, of women who left their country of origin, as well as of about fifty female volunteers belonging to the second generation of migrants. Nineteen Karen refugees were also monitored before their departure and after arriving in the US, as well as 36 persons born in the US or from Europe.
Some indigenous bacteria disappear
These different analyses indicated that the microbiota is much more diverse and abundant in people living in Thailand than in immigrants. Microbiotas of migrants and native-born Americans were similar. More precisely, the researchers reported the disappearance of some bacteria in favor of others, suggesting that the migrants’ flora goes through a “westernization” process, and all within a few months. Consequence: first- and second-generation migrants have lost an enzyme able to degrade complex sugars (especially vegetable fibers), which is naturally absent in native-born Americans but abundant in Thai people still living in their country of origin.
Diet cannot explain everything
Researchers consider that dietary changes alone cannot explain these variations. The scientists indicated that “although children of immigrants and native-born Americans followed a different diet, surprisingly, their microbiotas were still similar”. They also pointed out that exposure to antibiotics, stress or different drinking water could also induce these disruptions. Finally, they moderated their results by indicating that it was still too early to conclude that these changes are caused by migration, or to state that they directly contribute to the high incidence of obesity in US immigrants.
Vangay et al. US Immigration Westernizes the Human Gut Microbiome. 2018, Cell 175, 962–972 November 1, 2018