The major benefit of the most popular surgeries is their ability to decrease food intake while allowing the patient to feel full and relatively satisfied. The surgery gives the patient a tool to help her navigate in a world of high-volume and high-calorie eating.

Most of the medical benefits stem from weight loss. Everything from high blood pressure to sleep apnea (shallow breathing and frequent prolonged periods between breaths) are improved by significant weight loss:

• As many as 8 out of 10 patients with sleep apnea can improve to the point that they no longer need devices to help them get enough oxygen into their lungs and bloodstream during the night.
  
  
• Arthritis often improves, too. Weight-bearing joints, such as the knees, hips and ankles, often become less painful with the decrease in stress and pressure that the weight causes.
  
  
• Trouble with controlling urination, as well as excess swelling of the legs and ankles, are usually improved in proportion to the amount of weight lost.
  
  
• For people with type 2 diabetes, the surgeries also help regulate blood sugar. The antidiabetic effects come both from weight loss, which improves the effectiveness of the insulin made by the patient's body, and from a very positive effect caused by a change in the way food is absorbed, since, with a portion of the small intestines and stomach bypassed, fewer calories pass through. There is also a change in certain hormones the body produces. These effects are only beginning to be fully understood, but can lead to rapid and exciting improvement in blood sugar control.