The purpose of this study is to evaluate the effect of sitagliptin on gastric emptying, intragastric meal distribution, postprandial glycemia and insulinemia in healthy subjects. Glucagon-like peptide-1 (GLP-1) inhibits gastric emptying, thereby slowing the delivery of nutrients, and their absorption, across the small intestine. The rate of entry of carbohydrate into the small intestine is especially important in patients with diabetes mellitus. Sitagliptin is an orally administered inhibitor of dipeptidyl-peptidase-IV (DPP-IV), the enzyme responsible for the degradation of GLP-1. It is hypothesized that sitagliptin will increase the GLP-1 response to, and thereby slow gastric emptying and diminish the glycemic response to, a carbohydrate-containing meal.