Roux-En-Y Gastric Bypass Is Associated With Hyperinsulinemia But Not Increased Maximal Beta-Cell Function

Context: Roux-en-Y gastric bypass (RYGB) is associated with postprandial hyperinsulinemia.Objective: This study assessed whether increased blood insulin levels may be due to an increase in maximal beta-cell function.Design, Setting, and Participants: We performed a cross-sectional study at Columbia University Medical Center, New York, New York. Subjects without a history of diabetes were studied after surgery (n = 12) and were compared with nonsurgical controls (n = 10) who were mean matched for body mass index, insulin sensitivity, and hemoglobin A1c and with nonobese controls (n = 8).Methods: Subjects underwent a mixed-meal tolerance test and on a separate day an intravenous glucose tolerance test followed by a hyperglycemic clamp (450 mg/dL; 25 mM blood glucose) and arginine stimulation. The main outcome measure was maximal insulin secretion quantified after arginine stimulation (AinsRmax).Results: The RYGB group exhibited greater peak postprandial glucose levels and fourfold greater peak insulin levels than control groups; however, there were no significant differences in insulinogenic index or AinsRmax. Another finding was significantly greater postprandial glucagon levels in the RYGB group compared with controls.Conclusions: Our results suggest that after RYGB, the increase in postprandial levels of insulin are not due to changes in maximal beta-cell function but appear to be an appropriate response to altered nutrient flow and absorption. Copyright (C) 2019 Endocrine Society.