Brown fat cells help generate body heat using triglycerides stored in lipid droplets as energy, but it’s unclear whether those lipids are required. The Farese/Walther lab generated mice lacking triglycerides in brown adipose tissue by deleting enzymes that synthesize the lipids. Described in Cell Reports, the work showed that brown fat tissue is functional without triglycerides and that the triglyceride-lacking mice were able to maintain body temperature in the cold. The brown fat cells in these mice instead used circulating glucose and fatty acids and stored glycogen to fuel thermogenesis.