A Study to Examine Changes in GIP Plasma Levels Following Gastric Bypass Surgery in Obese Patients

Obesity is a multinational epidemic. There is evidence that despite educational measures and increased public awareness, the number of obese individuals continues to increase. Of the numerous obesity-related comorbidities, type 2 diabetes remains one of the most significant in terms of mortality and health care costs. Gastric Bypass Surgery (GBS) not only offers an effective form of therapy for morbid obesity, but also amelioration of type 2 diabetes mellitus. The normalization of glucose levels in GBS patients occurs within days after surgery and has been shown in surgical literature to be independent of the weight loss after surgery. The proximal gut, the site of release of certain incretins, may play a role in glucose homeostasis in obese individuals with type 2 diabetes mellitus. One such incretin is GIP, which when released into the circulation during the immediate postprandial period, accentuates the insulin response to a glucose meal. It is hypothesized that overactivity of this enteroinsular axis in obese individuals produces cell resistance to insulin and subsequent type 2 diabetes mellitus. A previous study reported elevated fasting GIP levels, as well as an exaggerated GIP response to a glucose meal, in obese subjects, which was significantly reduced months after GBS following weight loss. This pilot study of obese patients scheduled for GBS will compare the serum levels of certain peptides, including GIP, following a glucose meal before and after GBS, before weight loss has occured. In order to reproduce the preoperative state, and therefore to demonstrate the physiologic change, a small group of subjects who undergo open surgery will undergo the same measurements after surgery, but using a model in which the meal traverses the stomach, duodenum and jejunum with the aid of a gastrostomy tube.