Existing surgeries help with weight loss in different ways.
Restrictive surgeries work by shrinking the size of the stomach and slowing down digestion. A normal stomach can hold about 3 pints of food. After surgery, the stomach may at first hold as little as an ounce, although later that could stretch to 2 or 3 ounces. The smaller the stomach, the less you can eat. The less you eat, the more weight you lose.
Malabsorptive/restrictive surgeries change how you take in food. They give you a smaller stomach and also remove or bypass part of your digestive tract, which makes it harder for your body to absorb calories. Doctors don't do purely malabsorptive surgeries -- also called intestinal bypasses -- anymore because of the side effects.
Implanting an electrical device, the newest of the three techniques, prompts weight loss by interrupting nerve signals between the stomach and the brain.
How it works: The surgeon uses an inflatable band to squeeze the stomach into two sections: a smaller upper pouch and a larger lower section. The two sections are still connected by a very small channel, which slows down the emptying of the upper pouch. Most people can only eat a 1/2 to 1 cup of food before feeling too full or sick. The food also needs to be soft or well-chewed.