Effect of weight loss by gastric bypass surgery versus hypocaloric diet on glucose and incretin levels in patients with type 2 diabetes.

Abstract

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. 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. 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. This outpatient study was conducted at the General Clinical Research Center. 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. 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. 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.