When immigrants arrive in the United States, their gut microbiomes start to change. The native strains of bacteria that they bring from other continents are replaced by those found more commonly in Westernised bodies and the overall diversity is lost. This fascinating discovery was made by researchers at the University of Minnesota and the Somali, Latino and Hmong Partnership for Health and Wellness. It was published in the scientific journal Cell.
According to the study, moving to the US can seriously mess with immigrants’ microbiomes. “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,” says lead author Dr Dan Knights, a computer scientist and quantitative biologist at the University of Minnesota. Some of the strains they lose are the ones that help them break down and glean nutrients from fibres found in Southeast Asian staples like wild greens, coconut and tamarind.
The researchers began the study with the assistance and inspiration from Minnesota’s large community of refugees and immigrants from Southeast Asia, particularly the Hmong and Karen peoples, ethnic minorities that were originally from China and Burma and that, today, have communities in Thailand. They adopted a novel community-based participatory research method wherein members of the Hmong and Karen communities in Minnesota and Thailand were involved in designing the study, recruiting participants and educating their communities about the findings.
The team of researchers compared gut microbiota of Hmong and Karen people still living in Thailand; Hmong and Karen people who had immigrated to the US; the children of those immigrants; and Caucasian American controls. Much to their advantage, they were also able to follow a group of 19 Karen refugees as they relocated from Thailand to the US, allowing them to track how the refugees’ gut microbiomes changed longitudinally in their first six to nine months in the US.
The researchers were surprised to find that significant changes happened fast. In the first six to nine months, the Western strain Bacteriodes began to displace the non-Western bacteria strain Prevotella. This Westernisation also continued to happen over the course of the first decade in the US, and overall mircobiome diversity decreased, the longer the immigrants had been in the US. Analysing the participants’ food logs suggested that eating a more Western diet played a role in perturbing the microbiome but could not entirely explain all the changes.
Other studies have shown that people in developing nations have a much greater diversity of bacteria in their gut microbiome, the population of beneficial microbes living in humans’ intestines, than people living in the US. “But it was striking to see this loss of diversity actually happening in people who were changing countries or migrating from a developing nation to the US,” says Dr Knights. Lead author, Dr Pajau Vangay, added, “Obesity was a concern that was coming up a lot for the Hmong and Karen communities here. In other studies, the microbiome had been related to obesity, so we wanted to know if there was potentially a relationship in immigrants and make any findings relevant and available to the communities.”
The researchers also learnt that changes in the microbiome were even more pronounced in the children of immigrants. “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. 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,” explained Dr Knights. It should be noted that the research was not able to establish a cause and effect relationship between micrbiome changes in immigrants and the immigrant obesity epidemic. However, it did show a correlation that greater Westernisation of the microbiome was associated with greater obesity.
Dr Knights is of the belief that this research conveys a lot about our health. “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,” he said. “This might not always be a bad thing, but we do see that Westernisation 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.”
