Thioesterase superfamily member 1 (Them1), a BAT-enriched long chain fatty acyl-CoA thioesterase, is upregulated by cold and downregulated by warm ambient temperatures. Them1 (-/-) mice exhibit increased energy expenditure and resistance to diet-induced obesity and diabetes, but the mechanistic contribution of Them1 to the regulation of cold thermogenesis remains unknown. Them1 may act as a break on uncontrolled heat production and limit the extent of energy expenditure. Pharmacologic inhibition of Them1 could provide a targeted strategy for the management of metabolic disorders via activation of brown fat.