Enhanced thermic effect of food after roux-en-Y gastric bypass surgery

Context: The mechanisms of weight loss after Roux-en-Y gastric bypass (RYGB) surgery are incompletely understood. Objective: Our objective was to investigate changes in metabolic processing of ingested food that may contribute to the weight-reducing effect of RYGB surgery. Design and Setting: This was a cross-sectional case-control study at the Interdisciplinary Obesity Center, Cantonal Hospital St. Gallen, St. Gallen, Switzerland. Patients: Ten formerly obese women (mean±SEM body mass index [BMI] ±26.6±0.9 kg/m2) who had undergone RYGB surgery 41.9 ± 9.7 months before, 8 severely obese women (BMI ± 40.8 ± 2.0 kg/m2), and 10 lean women (BMI ± 20.9 ± 0.6 kg/m2). Intervention: Intervention was a standardized liquid meal test. Main Outcome: The thermic effect of food (TEF), respiratory quotient, and circulating levels of glucose, insulin, and C-peptide were assessed before and repeatedly during the first 90 minutes after the ingestion of a standardized liquid mixed meal containing 39.2 g carbohydrates, 15.4 g protein, and 2.8 g fat. Results: TEF area under curve (0-90 minutes) was significantly greater in RYGB patients than in severely obese and lean women (both P ± .01). After ingestion of the mixed meal, the respiratory quotient increased to significantly greater values in the RYGB patients than in the severely obese and lean group (P ± .001 for ANOVA time ± group interaction). Also, the postprandial rise in circulating glucose, insulin, and C-peptide levels was remarkably higher in the RYGB patients than in the other 2 groups (all P ± .001 for ANOVA time ± group interaction). Conclusion: Data demonstrate an enhanced TEF after RYGB surgery. Although this observation likely contributes to the weight-reducing effects of the surgery, data also point to an altered metabolic processing of food in RYGB patients characterized by an enhanced glucose absorption and postprandial carbohydrate oxidation.