 In this study obese youths 12-18 years will undergo MRI magnetic resonance imaging measurement of liver lipid content to determine hepatic fat content. They will undergo a sugary drink 75 grams of glucose and 25 grams of fructose challenge and Hepatic de novo lipogenesis will be determined as the incorporation of deuterium, from deuterium labeled water D2O, into plasma triglycerides. Subjects will undergo a 6 hours study assessing de novo lipogenesis, an oral glucose tolerance test, dual energy x-ray absorptiometry, magnetic resonance imaging, and Euglycemic-Hyperinsulinemic Clamp. 