"Gastric bypass surgery (GBP) and vertical sleeve gastrectomy (VSG) result in 40% weight loss with normalization of metabolism in severely obese patients. Protein deficiencies have been described after bypass surgeries. Guidelines recommend protein supplementation after the surgery, but without evidence based data to support these recommendations. Dietary proteins have positive effects on energy homeostasis by inducing satiety, maintaining lean body mass and increasing resting energy expenditure during calorie restriction, but may promote insulin resistance. Our goal is to test the effect of standard (SP) or high (HP) levels of dietary protein supplementation in patients undergoing GBP and VSG, randomized to SP or HP, and studied before and up to 24 months after surgery. Compared to SP supplementation, HP supplementation will:1) Reduce the improvement in glucose homeostasis and in insulin sensitivity2) Prevent protein turnover3) Decrease 24-h energy expenditure4) Maintain a greater lean body mass5) Increase satiety to a greater degree6) Patients after VSG, a restrictive only surgery, will fair better than after GBP, a restrictive and malabsorptive surgery, in terms of protein balanceThis study will help develop evidence-based clinical recommendation for safe and efficient dietary protein supplementation and stratify risk during surgical weight loss."