Fig. 1.

Sympathetically activated thermogenesis in brown adipose tissue, lipid mobilization from white adipose tissue, and induction of beige cells. Sympathetic nerve activity in adipose tissues is increased in response to cold exposure and oral ingestion of some food ingredients through the activation of transient receptor potential channels (TRP). Noradrenaline binds to β-adrenergic receptors (βAR) and initiates signaling cascades for triglyceride (TG) hydrolysis. The released fatty acids activate uncoupling protein 1 (UCP1) and are oxidized to serve as an energy source of thermogenesis. Activated UCP1 uncouples oxidative phosphorylation from ATP synthesis and dissipates energy as heat. Chronic sympathetic activation produces not only brown fat hyperplasia but also an induction of beige cells in white fat, thereby increasing whole-body energy expenditure and decreasing body fat.