Does brown adipose tissue (BAT) pack a big punch? Sure, BAT thermogenesis plays a major role in maintaining body temperature in human infants and small animals, but its relevance to body weight regulation in adult humans is intensely controversial. New technologies confirming the presence of functional BAT in adult humans add fuel to the fire. In this session, two leaders in this field will provide contrasting opinions in a ‘hot’ debate of the potential metabolic significance of BAT in humans.