Bariatric surgery is currently the most effective modality for treating severe obesity with evidence to support long-term sustained weight loss and improvement in obesity-related comorbidities. The two most commonly performed bariatric surgical procedures are the Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG). RYGB leads to greater weight loss than SG and improved diabetes control in patients following surgery. Despite the success of RYGB and SG in inducing weight loss and improving comorbidities, the underlying mechanisms leading to clinical improvement following these operations is not completely understood. Multiple factors are thought to play a role including reduced caloric intake, decreased nutrient absorption, increased satiety, release of hormones and shifts in bile acid metabolism.