<P> Brown fat or brown adipose tissue (BAT) is a specialized form of adipose tissue important for adaptive thermogenesis in humans and other mammals . BAT can generate heat by "uncoupling" the respiratory chain of oxidative phosphorylation within mitochondria through tissue - specific expression of uncoupling protein 1 (UCP1). BAT is primarily located around the neck and large blood vessels of the thorax, where may effectively act in heat exchange . BAT is robustly activated upon cold exposure by the release of catecholamines from sympathetic nerves that results in UCP1 activation . BAT activation may also occur in response to overfeeding . UCP1 activity is stimulated by long chain fatty acids that are produced subsequent to β - adrenergic receptor activation . UCP1 is proposed to function as a fatty acid proton symporter, although the exact mechanism has yet to be elucidated . In contrast, UCP1 is inhibited by ATP, ADP, and GTP . </P> <P> Attempts to simulate this process pharmacologically have so far been unsuccessful . Techniques to manipulate the differentiation of "brown fat" could become a mechanism for weight loss therapy in the future, encouraging the growth of tissue with this specialized metabolism without inducing it in other organs . </P> <P> Until recently, brown adipose tissue was thought to be primarily limited to infants in humans, but new evidence has now overturned that belief . Metabolically active tissue with temperature responses similar to brown adipose was first reported in the neck and trunk of some human adults in 2007, and the presence of brown adipose in human adults was later verified histologically in the same anatomical regions . </P> <P> Browning of WAT, also referred to as "beiging", occurs when adipocytes within WAT depots develop features of BAT . Beige adipocytes take on a multilocular appearance (containing several lipid droplets) and increase expression of uncoupling protein 1 (UCP1). In doing so, these normally energy - storing adipocytes become energy - releasing adipocytes . </P>

Fats that are stored in muscle and adipose tissue