The fuels being oxidized cas be determined empirically using a respiratory exchange ratio, which is the ratio of moles of CO2 produced per mole of oxygen (O2) consumed, or a respiratory quotient (RQ) if the animal is in a steady state; RQ values of 1.0. 0.7 and 0.8 are typically used for complete oxidation of carbohydrate, lipid and protein, respectively (Frayn, 1983).