Bariatric surgery (or weight loss surgery) includes a variety of procedures performed on people who are obese. Long term weight loss through the standard of care procedures (Roux en-Y bypass, sleeve gastrectomy, and biliopancreatic diversion with duodenal switch) is largely achieved by altering gut hormone levels responsible for hunger and satiety, leading to a new hormonal weight set point. Bariatric surgery is the most effective treatment causing weight loss and reducing complications of obesity.