However, studies quantifying the incretin effect in type 2 diabetes before and after treatment with either vildagliptin [72] or sitagliptin [73] (DPP-4 inhibitors) surprisingly do not find an augmented effect (Fig. 6d,e,k,l), mainly because GLP-1 concentrations and insulin secretion are elevated both with oral glucose and with ‘isoglycaemic’ glucose infusions, even though, in the latter case, these GLP-1 concentrations remain in the low (basal) range [72, 73]. Here, INS is linked to type 2 diabetes mellitus.