GIP and type 2 diabetes mellitus: As demonstrated by Michael Nauck using hyperglycemic clamp studies [144], and later confirmed by other studies [[147], [148], [149], [150], [151]], the insulinotropic effect of GIP is strikingly reduced in people with T2D relative to healthy controls, while the insulinotropic [144,151,152] and glucagon-inhibitory effects [153,154] of GLP-1 are largely preserved.