This study also aims to investigate the differences between the three groups in postprandial serum insulin, serum glucagon, plasma free fatty acids (FFAs), serum triglycerides, serum leptin, and serum gastrointestinal hormones: polypeptide YY (PYY), active glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), amylin, cholecystokinin, and ghrelin in individuals with overweight or obesity and T2D. This evidence concerns the gene GCG and obesity due to melanocortin 4 receptor deficiency.