Efficacy of Pharmacological Stimulation of BAT and WAT in Lean and Obese Young Adults

To determine whether pharmacological stimulation of supraclavicular Brown Adipose Tissue (BAT or "Brown Fat") and subcutaneous White Adipose Tissue (WAT) using an FDA-approved beta3 agonist is as effective in increasing oxidative metabolism in BAT and WAT as is the exposure to cold, the investigators will assess the efficacy of an FDA approved beta3 agonist Mirabegron (trade name Myrbetriq, Astellas Pharma, Inc.) for increasing oxidative metabolism in supraclavicular BAT and subcutaneous WAT in lean and obese young adults. The investigators anticipate that both methods to stimulate supraclavicular BAT and subcutaneous WAT will result in similar 18F-labeled fluoro-deoxyglucose (FDG) tracer uptake on positron emission tomography (PET) images as well as oxidative metabolism. This would demonstrate that pharmacological stimulation of BAT is effective and could lead to further, more detailed clinical trials in obese subjects.