Figure 4.Components of the energy budget of a human and a mouse at 21oC. At this temperature the human has no thermoregulatory requirement so the budget consists only of the basal energy expenditure (BEE), the thermic effect of food (TEF), and the Activity energy expenditure (AEE) comprising Non-exercise activity thermogenesis (NEAT) and physical exercise. In the mouse there is additionally the thermoregulatory demand (Treg) because it is 10oC below the lower critical temperature. Physical activity heat production may substitute for some of the thermoregulatory demands (shaded area so the components are no longer additive).