For newcomers to the United States, the downside of immigration may be a rapid change in gut bacteria, researchers say.
Microbes in the digestive tract have a direct influence on digestion and overall health. This new finding could help explain health issues -- such as obesityand diabetes -- that often affect immigrants in the United States, the study authors said.
"We found that immigrants begin losing their native microbes almost immediately after arriving in the U.S., and then acquire alien microbes that are more common in European-American people," said senior study author Dan Knights.
"But the new microbes aren't enough to compensate for the loss of the native microbes, so we see a big overall loss of diversity," said Knights, a computer scientist and quantitative biologist at the University of Minnesota.
For the study, the researchers compared the gut bacteria population ("microbiome") of four groups: Hmong and Karen people living in Thailand; Hmong and Karen people who emigrated to the United States; the children of those immigrants; and white Americans (the "control" group).
The study was published Nov. 1 in the journal Cell.
The findings showed that the changes were greatest in immigrants' children.
"We don't know for sure why this is happening. It could be that this has to do with actually being born in the U.S.A. or growing up in the context of a more typical U.S. diet," Knights said in a journal news release.
"But it was clear that the loss of diversity was compounded across generations. That's something that has been seen in animal models before, but not in humans," he added.
"When you move to a new country, you pick up a new microbiome. And that's changing not just what species of microbes you have, but also what enzymes they carry, which may affect what kinds of food you can digest and how your diet interacts with your health," Knights said.
That's not always a bad thing, he said. But in this case, "Westernization of the microbiome is associated with obesity in immigrants, so this could be an interesting avenue for future research into treatment of obesity, both in immigrants and potentially in the broader population," Knights concluded.