Gastric bypass and a lap band differ in that the former results in food bypassing a large amount of the small intestine and the latter constricts the stomach so that less food can enter, states Mayo Clinic. They both help people lose weight, but bypass surgeries are usually more effective.
Gastric bypass surgeries, such as Roux-en-Y and biliopancreatic diversion with a duodenal switch, both function similarly to each other and are more invasive than a lap band surgery, explains Mayo Clinic. In both surgeries, the size of the stomach is reduced by either cutting across and sealing a large part of the organ away or removing a large part, respectively. Next, a section of the small intestine is cut and connected to the smaller stomach, causing food to bypass most of the small intestine. These surgeries not only reduce the amount of food it takes to feel full, they lower the absorption rate of calories and nutrients of the small intestine.
Lap band surgeries are easier to perform than other types of bariatric surgery, according to Mayo Clinic. This surgery involves placing an inflatable band around the stomach. The band is then inflated, producing two separate cavities in the stomach. The upper part is left smaller than the lower, limiting the amount of food a person eats. Depending on a patient's needs, doctors can adjust the tightness of the band to allow more or less food in the stomach.