Energy expenditure and thermogenesis: animal studies on brown adipose tissue.

Thermogenesis in brown adipose tissue is now regarded as being a major component in the normal energy expenditure of laboratory rodents, and variations in the level of thermogenesis in the tissue are important in the regulation of energy balance. Defective thermogenic responses to diet or to cold have been shown to be central to the development of obesity in various rodent models. The quantitative importance of brown adipose tissue thermogenesis to energy expenditure in species other than rodents has not been established, but it is clear that the tissue is present in a wide range of mammals. In particular, active brown adipose tissue has now been identified in adult humans, as well as in newborn infants.