 During visit 2 the investigators will measure body weight and the investigators will perform an energy expenditure measurement after 40 minutes of bed rest. The investigators will regularly measure temperature by a tympanic thermometer. The subjects will receive intravenous administration of the radioactive pharmacon 18F-FDG, 60 minutes after the administration of the 18F-FDG, and 18F-FDG PET-CT scan will be performed. After the 18F-FDG PET CT scans, the investigators will measure insulin sensitivity by performing an oral glucose tolerance test. 