Incretins are a group of gastrointestinal hormones that cause an increase in the amount of insulin released from the beta cells of the islets of Langerhans after eating. They also inhibit glucagon release from the alpha cells of the islets of Langerhans. As a result, they slow the rate of absorption of nutrients into the blood stream by reducing gastric emptying and may directly reduce food intake. The two main candidate molecules that fulfill criteria for an incretin are glucagon-like peptide-1 (GLP-1) and Gastric inhibitory peptide (or glucose-dependent insulinotropic polypeptide or GIP).