Increased Energy Expenditure and Energy Loss through Feces Contribute to the Long-term Outcome of Roux-en-Y Gastric Bypass on Diet Induced Obese Mouse Model

Abstract

Background Roux-en-Y gastric bypass (RYGB) has been proved to be more effective than other bariatric procedures in long-term on body weight loss and remission of diabetes. However, the mechanism remains poorly understood. Long-term change of energy metabolism after RYGB has rarely been reported. Objectives To investigate the long-term outcome of RYGB on mouse model and its mechanism from the perspective of energy metabolism. Methods High-fat diet induced obesity (DIO) mice were assigned to two groups receiving RYGB(n=8) and sham operation(n=7), followed by high-fat diet feeding until 12 weeks after surgery. Body weight and food intake were recorded weekly, measurement of body composition and energy metabolism by metabolic chamber were conducted on week 4, 8 and 12 after surgery. Fecal energy measurement, Intraperitoneal Glucose Tolerance Test (IPGTT) and Insulin Tolerance Test (ITT) were conducted on week 12 after surgery.Results Food intake was reduced in RYGB group within the first 3 weeks after surgery and increased to be the same withSham group from postoperative week 4. At 12 weeks after surgery, body weight reduced by 36±3.2% in RYGB group comparing to 16±2% body weight gain in Sham group, while fat mass was significantly reduced in RYGB group than in Sham group (9.2±1.5% versus 30.1±0.7%). Energy expenditure was significantly higher on postoperative week 8 in RYGB group than in Sham group. In comparison with Sham group, respiratory exchange ratio (RER) was unchanged, decreased and increased in RYGB group at postoperative week 4, 8 and 12, respectively. Fecal energy measurementshowed that feces from mice in RYGB group contained higher energy level than Sham group. Glucose metabolism was significantly improved in RYGB group in contrast to Sham group, demonstrated by the result of Intraperitoneal Glucose Tolerance Test (IPGTT) (AUC: 1502± 104 versus 2277±198, respectively) and the Insulin Tolerance Test (ITT) (AUC: 524 ±50 versus 838±63, respectively). Conclusions Increased energy expenditure and energy loss through feces contribute to the long-term body weight control after RYGB. Enhanced glucose utilization might play a role in the long-term improvement of glucose metabolism.