Microbiome changes following immigration: Rethinking “Westernization” as an explanatory concept

An emerging focus in microbiome science is on changes to people's microbiomes following immigration, particularly to so-called Western countries, such as the USA, Canada, and Australia. Moving to these regions has been linked to microbiome changes that may increase immigrants' susceptibility to health problems, including obesity and Inflammatory Bowel Disease. The term "Westernization" (and adjacent terminology) is frequently used to describe changes in diet, lifestyle, and built environment - and the consequent microbiome shifts - associated with immigration. However, what Westernization means in this context, and whether it is an appropriate descriptor, is often unclear. The purpose of this article is to provide a review of the diverse meanings associated with the terms "West", "Western", "Westernization" (and similar) across microbiome-related research and broader uses. We argue that these terms can obscure the specific structural, environmental, and cultural factors shaping microbiome changes. We discuss the consequences of this imprecision and provide recommendations for future research. Avoiding oversimplified conclusions about what impacts immigrants' microbiome and health can contribute to more accurate targets for public health interventions for these groups in the long term.