There are a dozen different types of bariatric procedure, some more common than others. But they nearly all work by one of two principles: restriction of content or lowering absorption of nutrients.
Gastroplasty, for example, is a procedure in which the stomach is stapled near the top, altering its effective size. A smaller stomach has many effects, but the chief one is that it leads to a sense of fullness sooner. That discourages consuming large amounts of food, reducing calorie intake.
A similar procedure called Gastric Bypass (for which there are many names, such as Roux-en-Y GB, and wide variation in specific techniques) involves creating two unequal stomach compartments. The result is to reduce the available 'storage space' for food by about 95%. Food that enters this tiny stomach empties into the upper intestine.
A similar technique called Biliopancreatic Diversion or BPD is much less common today. In this method, about half the intestine is bypassed by being sliced and rejoined to the ileum near the end of the small intestine, 2-4 feet above the colon (large intestine).
It has the effect also of reducing absorption of ingested food inside the intestine, but can lead to nutrient deficiency. It's being replaced by less risky procedures with fewer side effects in many cases. One such is a variation that actually removes a section of the intestine, a procedure known as a Duodenal Switch, which creates a more cylindrical stomach. (Sometimes the two techniques are combined in a single surgery.)
There are other ways to reduce the volume of the gastrointestinal system and one is rapidly becoming the most popular for reasons of safety, convenience, and effectiveness. It is generically referred to as the lap band. The LAP-BAND® is an inflatable device from Allergan that is surgically wrapped around the stomach/intestine.
The plastic device is quite safe and rarely rejected by the body's immune system. It does require that the patient undergo periodic adjustments (usually four over 1-2 years). As the stomach shrinks from adjusting to containing and processing less food and weight loss proceeds, the band needs to be tightened if it's to continue being effective. That's done by a physician who injects saline into the device through a port lying just under the skin.
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