Changes in resting energy expenditure and body composition after weight loss following Roux-en-Y gastric bypass

Background: The objective of this study was to evaluate changes in resting energy expenditure (REE), body composition and metabolic parameters, and to investigate predictors of the results in seriously obese patients after Roux-en-Y gastric bypass (RYGBP). Methods: 31 patients (BMI 44.4 +/- 4.8 kg/m(2); 27 female, 4 male; 37.3 +/- 11.1 y) were evaluated at baseline and 6 months after RYGBP. Weight, REE, waist circumference (WC), fat mass (FM) and fat-free mass (FFM), physical activity, food intake, fasting glucose (GLU), insulin (INS), HOMA-IR and lipid concentrations were measured. Results: At 6 months, percentage of weight loss (%WL) was 29.0 +/- 4.4% and percentage of excess weight loss was (%EWL) 59.7 +/- 12.3%. FM loss corresponded to 77.1 +/- 12.2% of the weight loss. REE decreased from 33.4 +/- 4.1 to 30.1 +/- 2.6 kcal/kg FFM (P < 0.05). Significant decreases (P < 0.001) were observed in GLU, INS, HOMA-IR, LDL-cholesterol and triglycerides. %EWL was correlated with baseline INS (r = 0.44; P = 0.014), baseline HOMA (r = 0.43; P = 0.017), change in %FM (r = 0.67; P < 0.001) and change in WC (r = 0.5; P < 0.01). Decrease in REE/FFM (%) was positively correlated with baseline REE/FFM% (r = 0.51; P < 0.005) and change in %FM (r = 0.69; P < 0.001). Initial REE/FFM, baseline energy balance and FM change explain 90% of REE/FFM decrease. Conclusion: RYGBP was an effective procedure to induce significant weight loss, fat mass loss and improvement in metabolic parameters in the short term. Metabolic adaptation was not related to FFM wasting but to a higher baseline REE. Fasting hyperinsulinemia was the best single predictor of weight loss after RYGBP.