Several studies have reported a reduced basal [75] and postprandial secretion of GLP-1 in patients with T2DM, however, recent meta-analyses have not confirmed a significant impairment in GLP-1 secretion in individuals with T2DM or prediabetes compared to healthy controls, whether assessed after OGTT or a mixed meal [76–78]. Here, GCG is linked to type 2 diabetes mellitus.