| Outcome Measures: |
Primary: BAT net glucose uptake, will be assessed using i.v. injection of 18FDG with sequential dynamic PET/CT scanning., 2 years|BAT oxidative metabolism, will be determined using i.v. injection of 11C-acetate during dynamic PET/CT scanning, 2 years|BAT volume of metabolic activity, will be determined using a total body CT (16 mA) followed by a PET acquisition., 2 years|whole body organ glucose partitioning, will be determined using a total body CT (16 mA) followed by a PET acquisition be determined using a total body CT (16 mA) followed by a PET acquisition, 2 years | Secondary: lipolysis rate, will be measured using i.v. administration of \[13C\]-palmitate and \[2H\]-glycerol, using steele's non steady state equations, 2 years|Glucose appearance rate, will be determined using \[3-3H\]-glucose, 2 years|Energy expenditure, will be determined by indirect calorimetry from VO2 and VCO2 (Vmax29n, Sensormedics), 2 years|Insulin sensitivity, will be determined using the HOMA-IR (based on fasting insulin and glucose levels), 2 years|Insulin secretion rate, will be assessed using deconvolution of plasma C-peptide with standard C-peptide kinetic parameters, 2 years|β-cell function, will be assessed by calculation of the disposition index (DI) that is insulin secretion in response to the ambient insulin sensitivity., 2 years|metabolite responses, will be determined using a multiplex assay system, 2 years|Electrocardiogram, 2 years
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