Brown adipose tissue (BAT)

Brown adipose tissue (BAT) is your body's heat-generating fat. It is packed with mitochondria and a protein called UCP1. UCP1 lets the mitochondria release energy as heat instead of storing it as ATP. In adults, the active BAT depots sit mainly around your collarbones, spine, and neck. They switch on with cold and sympathetic signals (via β3-adrenergic receptors). BAT activity falls with age and with rising body fat. And lower activity goes with higher BMI, worse insulin sensitivity, and more cardiometabolic risk (in snapshot studies). You can boost BAT with cold exposure, β3-agonists, and candidate compounds like mirabegron and capsinoids. Whether sustained boosting actually improves metabolic health in humans is still being studied.

Last reviewed: June 22, 2026

This definition is educational and is not medical advice, a diagnosis, or treatment. Talk to a doctor about any health decisions. Read our full medical disclaimer