Brown adipose tissue (BAT) plays a fundamental role in maintaining body temperature by producing heat.BAT that had been know to exist only in mammals and the human neonate has received great attention for the treatment of obesity and diabetes due to its important function in energy metabolism,ever since it is recently reported that human adults have functional BAT.In addition,beige adipocytes,brown adipocytes in white adipose tissue (WAT),have also been shown to take part in whole body metabolism.Multiple lines of evidence demonstrated that transplantation or activation of BAT or/and beige adipocytes reversed obesity and improved insulin sensitivity.Furthermore,many genes involved in BAT activation and/or the recruitment of beige cells have been found,thereby providing new promising strategies for future clinical application of BAT activation to treat obesity and metabolic diseases.This review focuses on recent advances of BAT function in the metabolic aspect and the relationship between BAT and cancer cachexia,a pathological process accompanied with decreased body weight and increased energy expenditure in cancer patients.The underlying possible mechanisms to reduce BAT mass and its activity in the elderly are also discussed.