The transition from a non-westernized to westernized gut microbiome in Indian-Immigrants and Indo-Canadians is associated with dietary acculturation

Background: The growing immigrant population in North America is rapidly westernizing through the adoption of practices like reduced physical activity, changes in hygiene/medical practices, and acculturation of the westernized diet, commonly characterized by caloric dense, highly processed foods with low fiber intake. Amidst this backdrop are health disparities emerging in these populations. Furthermore, the global spread of industrialization raises concern for the increasing prevalence of modern diseases.1 For instance, inflammatory bowel disease (IBD) is increasing in prevalence globally, and alarming evidence reveals a specifically increased risk in young Indian immigrants and Indians born in several westernized countries.2-4 In 2019, India had an incidence rate of 2.34, whereas South Asians in Canada showed an incidence rate of 14.6 per 100,000 person-years, which was comparable to the general population in Canada.5,6 A likely contributor to this elevated risk in westernized countries like Canada may stem from changes in the gut microbiome as a response to living in an industrialized environment. The industrialized microbiome has been previously characterized by the decline of VANISH (volatile and/or associated negatively with industrialized societies of humans) taxa, frequently found in populations adhering to traditional lifestyles, and the rise of BloSSUM (bloom or selected in societies of urbanization/modernization) taxa, which appear in modern, industrialized individuals.7,8 Furthermore, health consequences following the assimilation into westernized culture have been previously documented. For example, non-industrialized Irish Travellers who adopted modern practices and Hmong and Karen migrants from Thailand who relocated to the United States (US) both experienced gut microbiome shifts that were associated with an increased risk for metabolic disorders.9,10 Currently, there is only one study published on the Indian immigrant gut microbiome, highlighting the gap in non-western/non-European microbiome research. Indeed, over 71% of all microbiome research comes from westernized cohorts, skewing our interpretation of a healthy human gut.11 Here, we aimed to investigate the distinction between the Indian and westernized gut microbiomes and the differences in the gut of Indians who migrate to Canada, alongside the adoption of the westernized diet.