Why are we seeing these changes in the human microbiota? Studies show that the western lifestyle promotes a suboptimal phenotype, in the sense that highly processed diets, sedentary living, lack of sun exposure, etc., results in a gene expression that leads to poor health and disease (1,2). However, we’re now learning that this gene-environment mismatch in many ways also involves the second genome in our bodies, in the sense that the western lifestyle is a