Metabolic rate analysis of healthy preterm and full-term infants during the first weeks of life

Background: Longitudinal data on resting energy expenditure (REE) in extremely immature infants and full-term neonates are scarce but are necessary to understand the energy requirements in neonatal nutrition during the first weeks of life. Objective: The aim of the present study was to measure REE and its main components longitudinally during the first weeks of life to quantify their significant determinants. Design: REE was investigated longitudinally over a period of 6 wk in healthy, stable, and growing preterm infants and over 5 wk in full-term neonates by means of indirect calorimetry. Results: A total of 197 infants, including 183 premature infants and 14 full-term neonates, were recruited for the study. REE values increased in all gestational age groups from the first week to 5-6 wk of postnatal age, with the most pronounced increase in the smallest infants (+140%) and the smallest increase in the fullterm neonates (+47%). Univariate calculations showed that for each postnatal week, REE increased by 6.93-9.64 kcal . kg(-1) . d(-1) with each additional kcal administered, for an average increase of 0.701 kcal, and increased by 1.78 kcal for each 1 g gain in weight. Postnatal age was the strongest predictor to influence REE (r(2) = 0.727, P < 0.0001). Conclusions: This study provides comprehensive data on longitudinally determined REE values of healthy premature and fullterm infants. Results may serve as a basis for comparative studies that address various disease states as well as different nutritional protocols. Am J Clin Nutr 2009;90:1517-24.