Effects of Weight Loss on Hepatic and Muscle Lipid Content and on Insulin Sensitivity on Obese Adolescents With NAFLD

Inclusion Criteria: * 10 to 21 yrs of age * Non-smoking * BMI \>95th percentile for age and gender, but BMI \<40 * Suspicion of fatty liver, with a high ALT (\>35) * Normal glucose tolerance or prediabetes (impaired glucose tolerance or impaired fasting glucose) Exclusion Criteria: * Females of child-bearing potential who are not using birth control * Pregnant or lactating females * Current medications except oral anti-diabetic medications and hormonal birth control * Lipid-lowering medication that increases liver enzymes * Significant kidney dysfunction (creatinine \>1.5 mg/dL) * Current heavy ethanol use or recent history of binge drinking * History or evidence of hepatitis A, B, or C, Wilson's Disease, or alpha-1-antitrypsin deficiency * Known to be HIV positive * Symptomatic angina pectoris or cardiac insufficiency as defined by the NYHA classification as Functional Class III or IV * Major vascular event within 6 months of screening (e.g. MI, stroke) * Active cancer within 5 years prior to screening * Current systemic disease, including type 1 or 2 diabetes * Enrolled in another research study within 1 month prior to screening * Implanted paramagnetic material (all subjects will need to fill out the Yale Magnetic Resonance Center safety checklist) * Anemia (HCT \<35%)