Effect of Weight Loss by Gastric Bypass Surgery Versus Hypocaloric Diet on Glucose and Incretin Levels in Patients with Type 2 Diabetes

Abstract

Abstract Context: Gastric bypass surgery (GBP) results in rapid weight loss, improvement of type 2 diabetes (T2DM), and increase in incretins levels. Diet-induced weight loss also improves T2DM and may increase incretin levels. Objective: Our objective was to determine whether the magnitude of the change of the incretin levels and effect is greater after GBP compared with a low caloric diet, after equivalent weight loss. Design and Methods: Obese women with T2DM studied before and 1 month after GBP (n = 9), or after a diet-induced equivalent weight loss (n = 10), were included in the study. Patients from both groups were matched for age, body weight, body mass index, diabetes duration and control, and amount of weight loss. Setting: This outpatient study was conducted at the General Clinical Research Center. Main Outcome Measures: Glucose, insulin, proinsulin, glucagon, gastric inhibitory peptide (GIP), and glucagon-like peptide (GLP)-1 levels were measured after 50-g oral glucose. The incretin effect was measured as the difference in insulin levels in response to oral and to an isoglycemic iv glucose load. Results: At baseline, none of the outcome variables (fasting and stimulated values) were different between the GBP and diet groups. Total GLP-1 levels after oral glucose markedly increased six times (peak:17 ± 6 to 112 ± 54 pmol/liter; P < 0.001), and the incretin effect increased five times (9.4 ± 27.5 to 44.8 ± 12.7%; P < 0.001) after GBP, but not after diet. Postprandial glucose levels (P = 0.001) decreased more after GBP. Conclusions: These data suggest that early after GBP, the greater GLP-1 and GIP release and improvement of incretin effect are related not to weight loss but rather to the surgical procedure. This could be responsible for better diabetes outcome after GBP.