Whole Body Protein Turnover and Urea Production of Preterm Small for Gestational Age Infants Fed Fortified Human Milk or Preterm Formula

Abstract

To investigate protein metabolism and urea production in preterm small for gestational age neonates fed a preterm formula or fortified human milk. Ten preterm small for gestational age neonates were fed either their own mother's milk fortified with a powdered protein mineral supplement or a special preterm formula. Protein metabolism was determined using constant steady-state infusion of L-[ring-2H5]phenylalanine and L-[1-13C]valine. Urea production was determined from steady-state [13C]urea kinetics. Mean protein intake was 24% higher in the preterm formula group than in the fortified human milk group. No differences in protein turnover, synthesis and breakdown were observed between the two groups, but protein accretion was 71% to 79% higher in the preterm formula group than the fortified human milk group. Urea production rates were not different in the two groups. There was a strong negative correlation between urea production and protein accretion calculated from phenylalanine kinetics but not when calculated from valine kinetics. Preterm formula and fortified human milk appear equally well tolerated by preterm small for gestational age neonates, but protein accretion was higher in the preterm formula group. In preterm small for gestational age infants, both phenylalanine and valine kinetic methods can be used to accurately determine protein metabolism.