GCG and obesity due to melanocortin 4 receptor deficiency: Now it is clear that there may be more complex factors, involving fermentation, modulation of intestinal absorption and the intestinal barrier, secretion of hormones related to appetite and insulin function (PYY, GLP-1, GLP-2), modulation of immunity and systemic inflammation, interference with topical deposition (obesity), and ectopic adipose tissue (steatosis) gene expression (151, 152).