- Subjects will be excluded if taking chronic medications known to adversely affect glucose homeostasis including thiazide diuretics, oral glucocorticoids, nicotinic acid, and beta-blockers. Subjects who have gained or lost more than 3 kg during the past 6 months will be excluded. Because of the PET scanning, all premenopausal women must have a negative pregnancy test within 24 hours prior to these procedures and this will be confirmed prior to each PET scanning session. These subjects will also be advised to use reliable contraceptive techniques during the study period. To avoid radiation exposure of the infant, women who are currently breastfeeding will not be permitted to participate in this research study. Subjects participating in Phase 2 and Phase 4 (that includes an MRI Scan) will be excluded if they have a contraindication to MRI such as surgical or vascular implants, pregnancy, pacemaker, or claustrophobia. In subjects with a questionable history of metallic fragments, an X-ray of the suspected area of the body will be performed to rule such out.