GIP and diabetes mellitus: Furthermore, we calculated the GIP/GLP-1 SR over time, assumed as an index of mutual incretin secretory dynamics, expressing the relationship between secreted levels of GIP and GLP-1 in response to a meal: compared to NGT and IGT people, DM subjects exhibited reduced GIP/GLP-1 SR (Fig. 1F, P = .02 for interaction time × glucose tolerance), possibly expressing an unbalanced overall incretin secretion in T2D.