Donald Trump, the Republican party, and their propaganda arm Fox News have been relentlessly promoting xenophobia by arguing that immigrants are coming to the US to kill people. But researchers Pajau Vangay and Dan Knights noticed something interesting and that is that the microbes in the guts of immigrants have a much greater microbe diversity than those of Americans. But the longer the immigrants live here, their guts change to match more closely the narrower gut diversity of the locals, and this narrowing gets more pronounced in the guts of their children. This is not necessarily a good thing because wider microbe gut diversity seems to be good for your health.

Many immigrants arrive in the U.S. healthy. But after living in this country for about a decade, they are at a very high risk of developing obesity. This is not just because these immigrants change their diets or increase caloric intake. Something else is going on. We believe that that part of the problem is a change in the trillions of microscopic creatures that live inside us all – the human microbiome.
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Having many different species of microbes in the gut is associated with good health.
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In our study, we found that the diversity of the gut microbes declined across generations of Hmong and Karen in the U.S. And individuals who were obese had an even greater decline in diversity.

We know from previous studies that in general, obese individuals have a lower microbe diversity in their guts than their lean counterparts. But obese Asians still had higher diversity than Asians who had immigrated to and were now living in the U.S. We also found that the children of immigrants had even fewer species of gut microbes than their parents. This suggests that the modern lifestyle in the U.S. may be causing each generation to lose more of their ancestral microbes.
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The obvious explanation for all of these changes is diet, since it is one of the strongest drivers of what species of microbes live in a person’s gut. We found that immigrants who lost Prevotella strains also lost highly specialized enzymes carried by those Prevotella for breaking down certain types of plants. These included palm, coconut, konjac and tamarind, which are commonly eaten in Southeast Asia. It is likely that the immigrants we studied had stopped eating some of these traditional foods after immigration, and the microbes that relied on those plant nutrients failed to grow and multiply and died off.

Although some of the microbes that U.S. immigrants begin to lose seem to be clearly related to changes in diet, we found that many species in the gut microbiome changed much faster and more drastically than their diet changed. We could not explain all of the changes in the gut microbiomes using dietary data alone, suggesting that there are likely other factors that are also affecting the microbiome. These factors could include water sources, antiparasitics or antibiotics, other medications, physical activity, mental health and other environmental exposures.

So when Donald Trump and the Republicans accuse immigrants of bringing diseases into the country and seeking to kill the people already here, it is actually the opposite. The immigrants are bringing in a lot of good microbes but America is killing a lot of them.