Fig. 1.

Reduced incretin effect in type 2 diabetes. The incretin effect was quantified in individuals with type 2 diabetes (b, e, h, l) and in age- and weight-matched healthy individuals (a, d, g, k) by administering oral glucose (50 g) or an i.v. glucose infusion (a, b), aiming for a matched (‘isoglycaemic’) glycaemic excursion (d–f) to provide the same degree of hyperglycaemia as the stimulus for insulin secretion. With oral glucose, incretin hormones are released from the gut (not shown) and augment the insulin secretory response (g–i) and C-peptide levels (j–l). The difference in insulin secretory response between oral glucose and isoglycaemic i.v. glucose stimulation is the incretin effect, usually expressed as a percentage of the insulin secretory response after oral glucose (c). This measure of the incretin effect is greatly reduced in patients with type 2 diabetes, whether calculated from insulin or C-peptide responses (c). p<0.05; n.s., not significant. Data from [2, 15]. (a, b, d, e, g, h, k, l) adapted from [2] with permission from Springer Nature