We have demonstrated that metformin has effects on bile acid metabolism, entero-endocrine hormone secretion and gut microbiome changes in patients with T2DM, challenging the concept that the glucose lowering effects of metformin are attributable solely to activation of AMPK [38], and antagonism of glucagon-mediated elevation of cAMP in the hepatocytes [39]. The gene discussed is GCG; the disease is type 2 diabetes mellitus.