Data from experiments with 25 growing pigs at high feeding level, with 12 adult mink on a varied energy supply and with 36 rats on a maintenance level were used in a biological model of nutrient oxidation, lipogenesis and retention at the whole body level. Nutrient oxidation was calculated from gas-exchange measurements in respiration chambers working according to indirect calorimetry principles. Lipogenesis and nutrient retention were measured by means of carbon and nitrogen balances, in accordance with the demonstrated model. The results demonstrated that growing pigs had a high level of protein retention and low protein oxidation. Digested carbohydrates were oxidized or used for lipogenesis. Oxidation of carbohydrate was the main energy sourer, while lipogenesis was the main source of fat retention. Independent of dietary fat level, pigs did not oxidize fat but used all dietary fat for body fat retention. The mink, being fed with high protein and fat levels but only a small amount of carbohydrate, use protein and fat as their main energy sources. Rats fed near-maintenance level used dietary carbohydrate as a main substrate for oxidation. It was demonstrated that the present model of nutrient oxidation, lipogenesis and retention in different animal species and at different dietary composition can be quantified by means of indirect calorimetry and measurements of carbon and nitrogen balances.