Energy expended by low birth weight infants in the deposition of protein and fat

One hundred twenty low birth weight infants were enterally fed diets containing fixed differences in protein and energy content. Serial, biweekly measurements were made of metabolizable energy intake, energy expenditure, nitrogen balance, and distribution of states of sleep, from the time the infants were receiving full enteral intakes (180 mL/kg.d) until weight reached 2200 g. Using multiple regression analysis of energy expenditure against protein stored, and metabolizable energy, the energy expended in the deposition of protein was calculated to be 5.5 kcal/g +/- 1.1 kcal/g (SE) and the energy cost of fat deposited was 1.6 kcal/g +/- 0.3 kcal/g (SE). Estimated maintenance energy expenditure of the nongrowing low birth weight infant was 42.3 +/- 3.2 kcal/kg/d. Variations in distribution of sleep state, an assessment of the activity state of the infant, did not explain additional variability in energy expenditure, after adjusting for protein and energy storage.