Adjusting energy expenditure for body weight in early infancy.

The most appropriate method of expressing energy expenditure relative to body weight was investigated in 50 normal, full-term infants at 6 weeks, 12 weeks and 6 months of age. Regression analysis revealed that the relationship between body weight and energy expenditure at each age could be adjusted for by expressing energy expenditure per kg0.65, per kg0.43 and per kg0.55 body weight at the three age points studied. These powers were not significantly different and a pooled estimate was per kg0.56. This is very close to kg0.5 or the square root of body weight. It is suggested that in studies on energy, metabolism in early infancy the expression of total energy expenditure per kg0.5 body weight should be used as the most appropriate adjustment for removing the influence of body weight upon energy expenditure.