Metabolic Impact of Dietary Protein Supplementation in Surgical Weight Loss

The obesity epidemic has grown rapidly in the United States, and is associated with increased morbidity and mortality rates. Bariatric surgery (BS) has emerged as the most effective treatment for severe obesity. Surgical weight loss (WL) is very significant (\~40-50kg) during the first 6-12 months after surgery. The adequate amount of dietary protein during the active period of surgical weight loss is not known. Dietary protein affects body weight regulation: satiety, thermogenesis, energy efficiency and body composition. During diet-induced energy-restriction, sustaining protein intake (PI) at the level of requirement (0.8g /kg ideal body weight (IBW)/ day) appears to preserve fat free mass (FFM) during active WL. PI above requirements (1.2g protein/Kg IBW/ day) results in favorable body composition changes, with greater decrease in fat mass and preservation of FFM, but without effecting WL. Dietary PI 0.8g/day has been associated with greater satiety and increased energy expenditure (EE) during calorie restriction. In this randomized prospective study, the investigators will evaluate the effect of PI on nitrogen balance, body composition, EE and satiety in 40 women undergoing either Gastric Bypass or Vertical Sleeve Gastrectomy, assigned to high protein supplementation (PRO-S), high PRO-S (1.2g /kg IBW/day) or standard- based current guidelines -PRO-S (0.8g /kg IBW/day). PRO-S will be supplied for 3 months after surgery. Outcome measures including nitrogen balance, body composition changes and satiety will be assessed at pre-surgery, and at 3, 6 and 12 months post-surgery. These results will help provide evidence-based data on safe and optimal levels of protein supplementation after BS