Lactate versus Alanine as Metabolic Fuel: The Cost of Nitrogen Removal The three carbons in lactate and alanine have identical oxidation states, and animals can use either carbon source as a meta- bolic fuel. Compare the net ATP yield (moles of ATP per mole of substrate) for the complete oxidation (to CO and HO) of lactate versus alanine when the cost of nitrogen excretion as urea is included. COO HO-C-H H-C-H H Lactate COO HN-C-H H-C-H Alanine