In people with severe obesity, gastric emptying and small intestinal transit time are slower compared to lean people and are associated with reduction in postprandial glucose absorption and glycaemic excursions as well as with reduced postprandial rise in GLP-1 and glucose-dependent insulinotropic polypetide levels (GIP) [43]. This evidence concerns the gene GLP1R and obesity due to melanocortin 4 receptor deficiency.