BACKGROUND The incretin effect is known to be decreased in type 2 diabetes. However, there are limited data on the incretin effect in non-Caucasian subjects. Because Asian patients with type 2 diabetes are characterized by decreased insulin secretion, this study set out to examine the incretin effect in Korean subjects with normal glucose tolerance (NGT) or type 2 diabetes.

METHODS We performed 75-g oral glucose tolerance tests (OGTTs) and corresponding isoglycaemic intravenous glucose infusion (IIGI) studies in Korean subjects with NGT (n = 14) or type 2 diabetes (n = 16). The incretin effect was calculated based on the incremental area under the curves (iAUCs) of the plasma levels of insulin, C-peptide or insulin secretion rate (ISR). The plasma levels of total glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) were measured by ELISA.

RESULTS The incretin effect was not different between the subjects with NGT and type 2 diabetes (43 ± 6% vs 47 ± 4%, P = 0·575 by insulin; 29 ± 7% vs 38 ± 4%, P = 0·253 by C-peptide; 28 ± 7% vs 35 ± 5%, P = 0·372 by ISR, respectively). However, the gastrointestinally mediated glucose disposal (GIGD) was markedly decreased in type 2 diabetes (28·5 ± 4·2% vs 59·0 ± 4·3%, P < 0·001). The plasma levels of the total GLP-1 and GIP during the OGTTs were comparable between the two groups.

CONCLUSION In Koreans, the secretion of GLP-1 or GIP during OGTTs and the incretin effect were comparable between subjects with NGT and type 2 diabetes, whereas the GIGD was significantly decreased in patients with type 2 diabetes.