The associations between microbiota and obesity, insulin resistance, and diabetes are presumably due to the impaired ability of the microbes to extract energy from the diet [9], altered fatty acid metabolism [11], changes in secretion of gut hormones such as peptide YY (PYY) [12], activation of lipopolysaccharide toll-like receptor-2 [13], and changes in the intestinal barrier integrity [14]. Here, PYY is linked to obesity due to melanocortin 4 receptor deficiency.