OBJECTIVE: This study investigated the associations of both physical activity time (PA) and energy expenditure (EE) with weight and fat mass (FM) loss in patients following Roux-en-Y gastric bypass (RYGB) surgery. METHODS: Ninety-six nondiabetic patients were included in this analysis. Post-RYGB patients were randomized in one of two treatments: a 6-month exercise training program (RYBG+EX) or lifestyle educational classes (RYGB). Body composition was assessed by dual-energy x-ray absorptiometry and computed tomography. Components of PA and EE were quantified by a multisensory device. Dose-response relationships of both PA and EE with weight loss and body composition were explored according to quartiles of change in steps per day. RESULTS: Patients in the highest quartiles of steps per day change lost more FM (3rd -19.5 kg and 4th -22.7 kg, p < 0.05) and abdominal adipose tissue (4th -313 cm2, p < 0.05), maintained skeletal muscle mass (3rd -3.1 cm2 and 4th -4.5 cm2, p < 0.05), and had greater reductions in resting metabolic rate. Decreases in sedentary EE and increases in light EE and age were significant predictors of both delta-weight and deltaFM (R2 = 73.8% and R2 = 70.6%, respectively). CONCLUSIONS: Nondiabetic patients who perform higher, yet still modest, amounts of PA following RYGB have greater energy deficits and lose more weight and FM, while maintaining higher skeletal muscle mass.

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