The idea was that patients could eat large amounts of food, which would be poorly digested or passed along too fast for the body to absorb many calories. The problem with this surgery was that it caused a loss of essential nutrients (malnutrition) and its side effects were unpredictable and sometimes fatal. The original form of the intestinal bypass operation is no longer used.

Surgeons now use other techniques that produce weight loss primarily by limiting how much the stomach can hold. Two types of surgical procedures used to promote weight loss are:

  Restrictive surgery. During these procedures the stomach is made smaller. A section of        your stomach is removed or closed which limits the amount of food it can hold and causes you    to feel full.

  Malabsorptive surgery. Most of digestion and absorption takes place in the small intestine.    Surgery to this area shortens the length ofthe small intestine and/or changes where it    connects to the stomach, limiting the amount of food that  is completely digested or absorbed    (causing malabsorption). These surgeries are now performed along with restrictive    surgery.

Through food intake restriction, malabsorption or a combination of both, you can lose weight since less food either goes into your stomach or stays in your small intestine long enough to be digested and absorbed.