brown fat A darker coloured region of adipose tissue found in newborn and hibernating animals (in which it may also be called the hibernating gland). Compared to normal white fat, deposits of brown fat are more richly supplied with blood vessels and have numerous mitochondria (hence the brown colour, due to the high concentrations of cytochrome oxidase). They can also be more rapidly converted to heat energy – a process that takes place in the fat cells themselves – especially during arousal from hibernation and during cold stress in young animals. Since the deposits are strategically placed near major blood vessels, the heat they generate warms the blood returning to the heart. Some types of obesity in humans may be linked to a lack of brown fat in affected individuals. See thermogenesis.

brown adipose tissue (brown fat) Metabolically highly active adipose tissue, which is involved in heat production to maintain body temperature, as opposed to white adipose tissue, which is storage fat and has a low rate of metabolic activity.

brown fat (brown) n. a form of fat in adipose tissue that is a rich source of energy and can be converted rapidly to heat. There is speculation that a rapid turnover of brown fat occurs to balance excessive intake of food and unnecessary production of white fat (making up the bulk of adipose tissue). Some forms of obesity may be linked to lack of – or inability to synthesize – brown fat.

fat, brown See brown adipose tissue.

brown fat See brown adipose tissue.