GIP, also known as gastric inhibitory polypeptide, or glucose-dependent insulinotropic polypeptide, is a 42-amino-acid peptide hormone synthesized in and secreted from K cells in the intestinal epithelium. There are two major GIP molecular forms in circulation, GIP (1-42) and GIP(3-42). Previous studies have demonstrated that GIP (3-42) is a degraded form of GIP (1-42) by the enzyme DPPIV. GIP secretion is primarily regulated by nutrients, especially fat. GIP exhibits potent incretin activity in rodent and human subjects. The primary action of GIP is the stimulation of glucose-dependent insulin secretion. GIP may also play a role in adipocyte biology.