Understanding differences in nutrient metabolism between premature and term neonates has important impli cations for the nutritional management of these infants in the neonatal intensive care unit. Prematurity and critical illness can impact the response to nutrient intake. Providing optimal nutritional support of both premature and critically ill neonates born at term remains an elusive challenge to neonatologists. Although less than 20% of extremely-low-birth-weight infants (ELBW) (<1000 g birth weight) are small for gestational age at the time of birth, growth failure is nearly universal by the time these infants approach discharge from the hospital. The long-term impact that early nutritional deficiencies may have on growth and neurodevelopment is only beginning to be appreciated.

It would seem obvious that there are substantial differences in metabolism between preterm and term infants, yet precisely defining those differences is surprisingly challenging. Metabolic studies in preterm and term infants have often been carried out using different techniques and under varied clinical circumstances, making comparisons difficult. Furthermore, information in normal term infants is often limited. Nevertheless, understanding developmental differences is fundamental to providing appropriate nutritional and metabolic support to preterm and term infants. This chapter will focus on presenting the differences between preterm and term infants with regard to protein, glucose, and energy metabolism.

Protein metabolism

A first step in understanding protein requirements is to assess protein losses under basal conditions.