The Effect of Standard Versus Longer Intestinal Bypass on GLP-1 Regulation and Glucose Metabolism in Patients With Type 2 Diabetes Undergoing Roux-en-Y Gastric Bypass: The Long-Limb Study

OBJECTIVE Roux-en-Y gastric bypass (RYGB) characteristically enhances postprandial levels of glucagon-like peptide 1 (GLP-1), a mechanism that contributes to its profound glucose-lowering effects. This enhancement is thought to be triggered by bypass of food to the distal small intestine with higher densities of neuroendocrine L-cells. We hypothesized that if this is the predominant mechanism behind the enhanced secretion of GLP-1, a longer intestinal bypass would potentiate the postprandial peak in GLP-1, translating into higher insulin secretion and, thus, additional improvements in glucose tolerance. To investigate this, we conducted a mechanistic study comparing two variants of RYGB that differ in the length of intestinal bypass. RESEARCH DESIGN AND METHODS A total of 53 patients with type 2 diabetes (T2D) and obesity were randomized to either standard limb RYGB (50-cm biliopancreatic limb) or long limb RYGB (150-cm biliopancreatic limb). They underwent measurements of GLP-1 and insulin secretion following a mixed meal and insulin sensitivity using euglycemic hyperinsulinemic clamps at baseline and 2 weeks and at 20% weight loss after surgery. RESULTS Both groups exhibited enhancement in postprandial GLP-1 secretion and improvements in glycemia compared with baseline. There were no significant differences in postprandial peak concentrations of GLP-1, time to peak, insulin secretion, and insulin sensitivity. CONCLUSIONS The findings of this study demonstrate that lengthening of the intestinal bypass in RYGB does not affect GLP- 1 secretion. Thus, the characteristic enhancement of GLP-1 response after RYGB might not depend on delivery of nutrients to more distal intestinal segments.