Between-subjects variation in energy expenditure: estimation of the effect of variation in organ size.

The between-subjects variation in energy expenditure over 24 h at a fixed physical activity and corrected for differences in fat and fat-free mass has recently been determined to be 6-7%. New data on the variation between subjects of the weights of the brain, liver, kidneys, heart and spleen together with estimates of the energy expenditure of these organs were used to calculate the part of the between-subjects variation in energy expenditure at a fixed physical activity that is due to this variation alone. The results show that this variation is close to 5%. Thus, a very considerable part of the total between-subjects variation can be explained by differences in the composition of the fat-free mass.