Basic-Alimentary TractGastric Bypass Increases Energy Expenditure in Rats

Background & AimsMechanisms underlying weight loss maintenance after gastric bypass are poorly understood. Our aim was to examine the effects of gastric bypass on energy expenditure in rats.MethodsThirty diet-induced obese male Wistar rats underwent either gastric bypass (n = 14), sham-operation ad libitum fed (n = 8), or sham-operation body weight-matched (n = 8). Energy expenditure was measured in an open circuit calorimetry system.ResultsTwenty-four-hour energy expenditure was increased after gastric bypass (4.50 ± 0.04 kcal/kg/h) compared with sham-operated, ad libitum fed (4.29 ± 0.08 kcal/kg/h) and sham-operated, body weight-matched controls (3.98 ± 0.10 kcal/kg/h, P < .001). Gastric bypass rats showed higher energy expenditure during the light phase than sham-operated control groups (sham-operated, ad libitum fed: 3.63 ± 0.04 kcal/kg/h vs sham-operated, body weight-matched: 3.42 ± 0.05 kcal/kg/h vs bypass: 4.12 ± 0.03 kcal/kg/h, P < .001). Diet-induced thermogenesis was elevated after gastric bypass compared with sham-operated, body weight-matched controls 3 hours after a test meal (0.41% ± 1.9% vs 10.5% ± 2.0%, respectively, P < .05). The small bowel of gastric bypass rats was 72.1% heavier because of hypertrophy compared with sham-operated, ad libitum fed rats (P < .0001).ConclusionsGastric bypass in rats prevented the decrease in energy expenditure after weight loss. Diet-induced thermogenesis was higher after gastric bypass compared with body weight-matched controls. Raised energy expenditure may be a mechanism explaining the physiologic basis of weight loss after gastric bypass.