ADJUSTING MILK INTAKE FOR BODY-SIZE IN EARLY INFANCY

Energy intake and expenditure are related to body size and body composition and therefore must be taken into consideration when comparing individuals. Previous work has typically expressed energy metabolism variables per kilogram body weight or per kilogram fat-free mass. However this may not remove the effect of body size entirely. In infancy milk volume intake is usually expressed in a similar manner which may not be entirely appropriate. The most appropriate method of expressing milk volume intake relative to body weight and fat-free mass was investigated in 20 normal breast-fed infants at 6 weeks of age. Regression analysis revealed that the relationship between milk intake and body weight could be adjusted for by expressing milk intake per kg(0.68), and that the relationship between milk intake and fat-free mass could be adjusted for by expressing milk intake per kg(0.54). These values are not significantly different to 0.50 which is the square root of body weight. It is suggested that in studies of energy metabolism in infancy the expression of milk intake per kg(0.50) should be used as the most appropriate adjustment for removing the influence of body size upon milk intake, in the first few months of life.