Immigration to US fosters obesity and changes microbiome

In November 2018, the University of Minnesota published a study on the “westernization” and the loss of immigrant’s innate gut microbiomes. This change comes along with a decrease of diversity and leaves immigrants with a tremendously greater chance for metabolic disease and obesity.

The study focused on a group of Thai women, living in rural Thailand and later immigrating to Minneapolis, USA. In Thailand the women fed on the traditional Thai cuisine – lots of rice, home-grown vegetables and practically no meat. With adapting the American lifestyle the women also took over all-American eating habits – that is lots of convenience food, rich in proteins and sugars. The obesity rate rose from 5% in Thailand to over 30% in the US within the very same group.

Thoroughly conducted study

This rise in obesity as such should not be any big surprise as an increase in BodyMass Index (BMI) is to be expected when switching from healthy Thai cuisine to American junk-food. However, the study deserves consideration as it thoroughly examined the participants’ microbiomes. The three groups were 1) a group of women living in southeast Asia, 2) the mentioned group of Thai women emigrating from rural Thailand to the US and 3) a group of second generation immigrant women, who were born and raised in the US, but their parents immigrated from southeast Asia. The control group were European-American women.

Nutrition is not the only thing

Remarkably, the change of eating habits seems to be only part of the problem. Even more important, the decrease of microbiome diversity seems to trigger later metabolic diseases. The study found that immigrants are losing their innate microbiome, such as enzymes for degrading plant fibres, as early as 6 months after arrival. The test group also showed a loss of the so called Prevotella that are typical for Asian microbiomes, and an increase in “western” Bacteroides. Along comes a reduced functionality of the digestive tract. For instance, carbohydrates such as resistant starch cannot be digested or fermented that easily.

Tremendous “westernization” of the microbiome

The longer immigrants live in the US, the more their microbiomes resemble the ones of the European-American control group. Only 6 to 9 months after arrival, the assimilation process starts and already the second-generation immigrants have a fully “westernized” microbiome with poorer functionality. But – and that is the core outcome of the study – 6 months after arrival, the eating habits have by far not assimilated to the western style. After 6 to 9 months, probands were consuming a multiple of rice compared to the European-Americans. However, the change in microbiomes has started as early as that – and that is an important indicator that nutrition does influence the microbiome, but not only.