GCG and obesity due to melanocortin 4 receptor deficiency: After Roux-en-Y gastric bypass (RYGB), patients with T2DM and obesity exhibit increased secretion of gut incretin peptides—PYY, GIP, GLP-1, and oxyntomodulin (Oxm)—that reduce food intake, delay gastric emptying, and enhance nutrient uptake [32,33,34].