GIP and type 2 diabetes mellitus: Of the two principal incretin hormones, GLP-1 plays a more important role in T2DM since the insulinotropic action of glucose-dependent insulinotropic polypeptide (GIP) is essentially lost in persons with T2DM, while the insulinotropic activity of GLP-1 following administration of pharmacological doses of GLP-1 is preserved [5].