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/m(2)) who had undergone RYGB surgery 41.9 +/- 9.7 months before, 8 severely obese women (BMI = 40.8 +/- 2.0 kg/m(2)), and 10 lean women (BMI = 20.9 +/- 0.6 kg/m(2)). 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 x 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 x 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. (J Clin Endocrinol Metab 98: 3776-3784, 2013)