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For very obese people who need more than diet and exercise, weight loss surgery can be lifesaving.

Depending on the type of weight loss surgery, patients often lose 30% to 50% of their extra weight in the first 6 months after surgery. Yet weight loss surgery is major surgery and does come with small but serious risks.

How Weight Loss Surgery Works

Weight loss surgery works in two ways: by restriction and malabsorption.


Surgeries that use restriction work by preventing the stomach from stretching to full size. Normally, the stomach can hold about 6 cups of food. After weight loss surgery, the stomach can hold only a cup or so. This results in feeling full faster, eating less, and losing weight.


Some weight loss surgeries divert food around a section of intestine as well as shrink the stomach. By skipping some of the intestine, fewer calories are absorbed. This leads to weight loss.

Most weight loss surgery today is laparoscopic. In laparoscopic surgery, the surgeon makes five to six small cuts in the belly wall. He inserts tiny tools and a camera through these holes, then operates while watching a video screen.

In open surgery, the surgeon makes one large cut along the middle of the belly. This is sometimes necessary, when the surgery cannot be done laparoscopically.

Types of Weight Loss Surgery

Roux-en-Y Gastric Bypass Surgery

This is the most common weight loss surgery done today, making up about 80% of all weight loss surgeries in the U.S.

There are two parts to a Roux-en-Y gastric bypass:

  1. The surgeon divides the stomach into a large portion and a much smaller portion. He then staples the small stomach portion to make a small pouch.
  2. The surgeon then disconnects the stomach pouch from the first part of the small intestine (the duodenum). The surgeon reconnects the stomach to the second part of the small intestine (the jejunum).This is the bypass.

After gastric bypass, you feel fuller after eating less food, so you lose weight. The bypass also makes you absorb fewer calories, so you lose more weight.

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