Last week, a really interesting new study[i] was published in the journal, Cell, detailing how immigrating to the USA negatively impacts the gut bacteria. Researchers looked at people from Southeast Asia and found that there was a significant reduction in the diversity of gut microbes with each subsequent generation, culminating with their microbiota resembling those of Americans of European origin.
You all know that a reduction in microbial diversity is associated with an increase in inflammatory health issues, including obesity. I’ve written about this several times before on this blog. 514 female immigrants to the Minnesota area, provided stool samples and diet diaries for this study. Some had lived in Thailand, some were first, and some second generation Americans. These were compared to the bacterial microbiomes of 36 Americans of European origin.
The dominant species of the recent immigrants was Prevotella but that changed remarkably quickly to Bacteroides. Prevotella is important in the digestion of high fiber foods, which are much more predominant in an Asian diet (as opposed to the “western” diet, which is heavy in sugar, fat and protein). Dan Knights, a co-author of the study, points to the change in diet as a key factor in this loss of diversity which changes within just a few months: “People began to lose their native microbes almost immediately after arriving in the U.S. The loss of diversity was quite pronounced: Just coming to the USA, just living in the USA, was associated with a loss of about 15 percent of microbiome diversity.” The children of these immigrants lost a further 10% of diversity. What’s really scary, and kind of amazing, is that “Even a short period of residence in the United States was sufficient to induce pronounced increases, in some cases over 10-fold, in the ratio of Bacteroides to Prevotella.”[ii]
The change in diet, and the loss of microbial diversity, was clearly associated with an increase in obesity and diabetes.
An important note: in the conclusion of the paper the authors of course point out the limitations of the study. While they looked at the diet/microbiome connection, they did not take into consideration changes in stress levels, exercise, drinking water, antibiotic use, and treatment with anti-helminth drugs. All of these, some more, some less, will also have an impact on the loss of microbial diversity. (In fact, in my next post, I’ll tell you about a different immigrant study from a couple of years ago, this one looking at Ethiopian immigrants to Israel and the health implications arising from the loss of their native helminth populations.)
Wouldn’t it be interesting to look at immigration the other way? What happens to the microbiota of Americans who move to less industrialized countries? Can this loss be reversed? The answer is currently unknown.
[ii] Vangay, P, et. al. US immigration westernizes the human gut microbiome. Cell. 2018;175(4):962-972.