Energy balance

Brown adipose tissue (BAT) is present and metabolically active in adult humans, where it contributes to energy expenditure and thermogenesis, challenging the prior belief that it is nonexistent or nonfunctional in adults.

You likely have active brown fat, even as an adult. It helps burn calories and regulate temperature. While you can't simply 'switch it on' with a pill without side effects, understanding its existence means your body has a built-in mechanism for energy expenditure that can be influenced by factors like cold exposure and diet.