Adipose tissues, which include white adipose tissue (WAT) and brown adipose tissue (BAT), play an essential role in regulating whole-body energy homeostasis. Recent studies also reveal the presence of a subset of cells in WAT that could be induced by environmental or hormonal factors to become ''brown-like'' cells, and this ''beigeing'' process has been suggested to have strong antiobesity and antidiabetic benefits. More recently, same studies showed that cold stress stimulate the browning of subcutaneous white adipose. However, to the investigators knowledge, there are no direct data that clearly show that cold stress can promote the browning of subcutaneous white adipose.

Individuals have cold exposure at 15C for 2 hr everyday for one week.Biopsy for subcutaneous white adipose was performed before and after one week cold exposure programme under local anesthesia. Measure the brown fat characteristics of biopsy samples. The expression levels of uncoupling protein-1 (UCP-1), peroxisome proliferator-activated receptor (PPAR)-r, peroxisome proliferator-activated receptor r coactivator 1 a (PGC1a) , growth factor receptor binding protein-10 (Grb10), PR domain containing 16 (PRDM16) will be determined before and after cold stress programme from the biopsy samples. In addition, a combination of PET and computed tomography (CT) - with the glucose analogue 18F-fluorodeoxyglucose (18F-FDG) as a tracer will be performed for brown adipose tissue before and after cold stress programme.

Inclusion Criteria:

• healthy men
• 18-60 years old
• BMI 20-28 kg/m2

Exclusion Criteria:

• BMI < 20 kg/m2
• BMI > 28 KG/M2
• Female