GLP1R and type 2 diabetes mellitus: Comparison of the actions of infused GLP-1 and GIP in human subjects with T2D, irrespective of the etiology of the disease, demonstrates that although the initial early phase of insulin secretion in response to GIP is preserved in diabetic subjects, the later phase from 20–120 min is characterized by a completely defective insulin response to GIP, even when higher concentrations of GIP are infused in study subjects, whereas the insulin secretory response to GLP-1 is preserved [24].