Body composition and energy expenditure were investigated in Angus heifers divergently selected for residual feed intake. Differences in fat deposition at rib and rump sites were observed between the lines but there was no difference in protein deposition, weight gain or energy expenditure. Most of the variation in energy expenditure could be accounted for by the metabolisable energy consumed by the animal. The implications of this observation on the biological consequences of selection for residual feed intake are discussed. These are preliminary observations and further work on the biological basis of the trait is required to provide definitive answers.