Studies employing intraduodenal infusion of nutrients at different rates that mimic the physiological range of gastric emptying have shown that the secretion of GIP and CCK increases in an approximately linear pattern with increasing rates of infusion in health, obesity and T2DM [154,155,156,157,158,159,160,161]. This evidence concerns the gene CCK and obesity due to melanocortin 4 receptor deficiency.