To study postprandial metabolism in lean, obese and T2DM adolescents using a mixed meal challenge. Specifically we will be measuring the following parameters of postprandial metabolism: 1. Postprandial glucose and triglycerides excursions 2. Gastric emptying 3. Insulin, amylin, glucagon, GLP-1 and ghrelin secretion 4. Glucose Turnover rate