Gastric bypass and other weight-loss surgeries make changes to your digestive system to help you lose weight by limiting how much you can eat or by reducing the absorption of nutrients, or both. Gastric bypass and other weight-loss surgeries are done when diet and exercise haven't worked or when you have serious health problems because of your weight.There are many types of weight-loss surgery, known collectively as bariatric surgery. Gastric bypass is one of the most common types of bariatric surgery in the United States. Many surgeons prefer gastric bypass surgery because it generally has fewer complications than do other weight-loss surgeries.