The investigators will perform a cross sectional analysis on the chinese adults who use 18F-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) to scan the whole body at Huashan Hospital from 2009 to 2013. BAT activity will be measured by PET/CT. Not only demographic data on sex, age, medication and medical history,but also data on body composition and physical examination will be collected for all subjects. Imaging date,outdoor temperature and fasting blood samples will be collected as well. In addition, the investigators will analyse the metabolic profiles in healthy adults with active BAT and their negative controls,such as lipid profiles,fasting glucose and insulin sensitivity, adipokines and other biochemical markers.