[Changes in body composition in patients following bariatric surgery: gastric bypass and sleeve gastrectomy].

Introduction: among the surgical techniques that promote greater weight loss are Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG). These procedures generate changes in muscle mass (MM) and fat mass (FM). Objective: the aim of this study was to determine changes in body composition in patients undergoing RYGB and SG in a period of one-year after surgery. Methods: a cross-sectional retrospective study was conducted in three clinical centers of bariatric surgery in the Metropolitan Region, Chile. Information on MM and FM was obtained through bioimpedance analysis of 96 women and 32 men, operated between 2013 and 2017. Results: RYGB operated subjects presented higher MM content preoperatively and at the end of the first year compared to SG. In the first six months, the loss for MM, FM and % total fat (%FM) was similar in both techniques. Men with RYGB present greater loss of MM and FM in the first trimester post-surgery than those who submitted to SG (p = 0.0453). Subjects submitted to RYGB presented higher weight and body mass index (BMI) in the preoperative (p = 0.0109); the BMI at the end was similar in both surgical techniques (p = 0.6936). The lost kilos of MM were greater in the subjects submitted to RYGB (p = 0.0042), however, the % loss of MM exceeds the recommended (up to 22%) in both techniques. Conclusion: the nutritional approach is necessary to increase protein intake pre- and post-surgery as well as physical activity in order to preserve this compartment.