New evidence explains why patients who undergo gastric bypass surgery get their diabetes symptoms under control quickly — often within days — while those who have lap-band surgery do not.
The key, researchers say, is the change in the position of the intestines. During gastric bypass surgery, the portion of the intestines closest to the stomach is removed so that it no longer receives nutrients. The lower portion is then attached directly to the stomach, thus receiving all of the incoming nutrients. Researchers say these positional changes "ramp up" production of blood sugar by the small intestines, which then send signals to the liver to decrease glucose production.
Besides removing a substantial portion of the stomach, gastric bypass reorganizes the intestines into two parts, study co-author Dr. Gilles Mithieux, from Universite de Lyon, said in a statement. The proximal portion no longer receives nutrients directly from the stomach, whereas the more distal portion of the intestines now receives direct output from the stomach.
These changes, according to Dr. Mithieux, cause an increase in glucose production. Specifically, the lower portion, which usually produces little glucose, increases its production, more closely resembling the upper portion in this regard. Sensors in the liver detect the elevated glucose and send an appetite-suppressing signal to the brain, which contributes to the satiety and weight loss seen with gastric bypass.
In the current investigation, the authors examined the effects of gastric bypass and gastric banding in mice. In addition to the link between gastric bypass and intestinal gluconeogenesis, they found that a glucose transporter called GLUT-2 is needed for the liver to sense glucose levels in the portal vein. Mice lacking GLUT-2 did not experience the enhanced glycemic control usually seen after gastric bypass.
These changes in the intestines increase insulin sensitivity and lower blood sugar, thus improving the symptoms of diabetes often within days of surgery; well before any weight loss takes place. In contrast, gastric banding — also called lap-band surgery — causes weight loss by placing a prosthetic band around the stomach, cutting hunger. Researchers say because it does not alter the intestines at all, it lacks the immediate metabolic benefits of bypass.
Furthermore, they note, sensors in the liver detect the elevated glucose and send an appetite-suppressing signal to the brain, which contributes to the satiety and weight loss seen with gastric bypass.
Study author Gilles Mithieux of Institut National de la Sante et de la Recherche Medicale in France advises patients considering either surgery to talk to their doctor about the risks and benefits of the procedures. He says these results support the notion that gastric bypass could be an effective treatment for diabetes in obese patients and could even have potential for patients who are diabetic but are not obese.
Cell Metabolism, 2008