ESTIMATION OF THE ENERGY-COST OF PHYSICAL-ACTIVITY IN INFANCY

Objective-To estimate physical activity energy expenditure (AEE) in gr oups of free living infants in the first year of life. Design-Mixed lo ngitudinal study of 124 healthy infants, using 232 estimations of AEE made between 1.5 and 12 months. Infants studied at more than one time point were treated as new cross sectional data points. Total energy ex penditure and body composition were estimated using doubly labelled wa ter. Sleeping metabolic rate was predicted from weight. Results-AEE in creased from 5% of energy intake at 1.5 months to 34% at 12 months. Gr owth costs declined by 90%, but metabolisable intake by only 20%, over the same period. Conclusions-Energy is increasingly diverted from gro wth to activity during infancy. Values for AEE may aid in estimating e nergy requirements of groups factorially. Further work is required, ho wever, on individual variability in AEE, and on the effects of disease , hospitalisation, surgery, and malnutrition.