Energy Expenditure Before and After Roux-en-Y Gastric Bypass

Weight loss may decrease the energy expenditure (EE) because of changes in body composition (BC). The reduction in EE may contribute, in part, to weight regain. Experimental studies in animals indicate that Roux-en-Y Gastric Bypass (RYGB) increases the resting metabolic rate (RMR) when adjusted for body weight (BW). Thus, the aim of this study was to assess the clinical effects of RYGB on EE in patients who have undergone RYGB. The study was prospective and included 46 RYGB patients whose RMR was assessed prior to and at least 6 months post-surgery by indirect calorimetry. BW and BC were measured at these same time points using bioelectric impedance. RMR was adjusted for changes in BW, i.e., kilocalories per kilogram. Statistical tests were used to analyze the results. The BW-adjusted RMR (kilocalories per kilogram) increased post-RYGB by 17.66 % (p < 0.0001). RMR adjusted for BW was negatively correlated to the total percentage of body fat preoperatively (r = -0.30729, p = 0.0378) and postoperatively (r = -0.46731, p = 0.0011) and was positively correlated to the fat-free mass percentage (%FFM) both preoperatively and postoperatively. Furthermore, BW-adjusted RMR and %FFM were positively correlated to percent excess weight loss (r = 0.55398, p < 0.0001 and r = 0.31677, p = 0.0283, respectively). Weight loss following RYGB is associated with an increase in BW-adjusted RMR and with %FFM. An increase in energy expenditure post-RYGB may be responsible, in part, for successful long-term weight loss of the RYGB procedure.