“When they came to the U.S. almost immediately they began losing their native microbes.” Dan Knights, a computational biologist at the University of Minnesota. “And over time the balance shifted to the point where they were dominated by the U.S. associated microbes.”

He’s referring to first- and second-generation immigrant women, from the Hmong and Karen ethnic minorities in southeast Asia. His team sequenced the DNA found in their feces.

And they saw that there was an immediate decline in the number and diversity of gut microbes among the immigrants, compared to their counterparts still living back home. And the decline continued over time.