GLP1R and type 2 diabetes mellitus: Of the two endogenous incretins GLP-1 and GIP, GIP is considered to predominantly mediate the incretin effect and post-prandial insulin release in healthy individuals [28,29,30]; however, multiple studies indicate that patients with type 2 diabetes almost completely lose their insulinotropic response to GIP, whereas that to GLP-1 is preserved [28,31].