In Gastric Bypass procedure, a small stomach pouch is created to restrict food intake. Next, a Y-shaped section of the small intestine is attached to the pouch to allow food to bypass the lower stomach, the duodenum (the first segment of the small intestine), and the first portion of the jejunum (the second segment of the small intestine). This bypass reduces the absorption of nutrients and thereby reduces the calorie intake.
Sleeve Gastrectomy procedure involves removing the lateral 2/3rds of the stomach with a stapling device. It can be done laparoscopically ( keyhole surgery) but is not reversible. It basically leaves a stomach tube instead of a stomach sack.
In Adjustable gastric banding procedure, a hollow band made of special material is placed around the stomach near its upper end, creating a small pouch and a narrow passage into the larger remainder of the stomach. The band is then inflated with a salt solution. It can be tightened or loosened over time to change the size of the passage by increasing or decreasing the amount of salt solution.