They found that levels of a particular bacteria called Prevotella, responsible for producing some of the enzymes that break down plant fiber, declined as the Hmong and Karen women spent more time in the US. At the same time, those of Bacteroides, a type associated with a westernized diet, shot up.
Overall, their microbiota started to look a lot more western – and like the white American controls'. This shake-up of bacteria in the gut was noticeable after just nine months on US soil but the change was most apparent among the children of immigrants.
Knights described this radical loss of diversity as "striking". “We don't know for sure why this is happening. It could be that this has to do with actually being born in the USA or growing up in the context of a more typical US diet,” he continued.
"But it was clear that the loss of diversity was compounded across generations. And that's something that has been seen in animal models before, but not in humans."
This would not be the first time diet (and obesity) has been associated with changes to the microbiome, particularly a microbiome that is less diverse – studies have linked microbiota to our waistlines, food cravings, and the food we eat as well as to changes in our mood, sleep, and behavior. But it is important to remember all this is showing is a correlation, it is not proving causation.
So, is the rise in obesity due to the change in microbiota? Or is a third factor – diet, environment, or both – affecting both microbiota and obesity rates? To find out, more research is needed.