Gastric bypass surgery works by making the stomach smaller and redirecting food to bypass part of the small intestine. The most common form of gastric bypass is referred to as Roux-en-Y (roo-en-y), named after the surgeon (César Roux) who first described it.
In the Roux-en-Y bypass procedure, the size of the stomach is permanently and irreversibly reduced to 10% of its original size – roughly to the size of a golf ball. The outlet of the stomach to the small intestine is also restricted.
The procedure is referred to as “bypass” because attachment of the stomach pouch to the small intestine is moved to a point below that at which the stomach normally passes food to the small intestine. As a result, food passes through a much smaller portion of the small intestine, reducing the amount of calories and nutrients absorbed. Because of this, many gastric bypass patients suffer dietary deficiencies and have to take supplemental vitamins by mouth or injection. Some gastric bypass patients may also experience gastrointestinal side effects caused by the “dumping” of food that is not fully digested. These side effects include nausea, vomiting, and diarrhea.