The gut microbiota usually affects the host metabolism via the regulation of its metabolite SCFAs, which can mediate the interaction between the gut and multiple organs by modulating glucose homeostasis, lipid metabolism, fatty acid oxidation, immune responses and insulin signaling, and have been proposed as valuable candidates in the prevention of obesity and T2D [47,56]. The gene discussed is INS; the disease is obesity due to melanocortin 4 receptor deficiency.