Amino acids and protein for preterm infants: How much and for what?

Protein and amino acids derived from protein digestion in the gastrointestinal tract or from intravenous infusions are fundamental for normal metabolism, growth, and neurodevelopmental outcomes in the fetus and the preterm infant of the same gestational age. Many studies support that at least 3.0-3.5 g/kg/day of protein or amino acids are needed to achieve normal nitrogen/protein balance and growth rates and the large fractional increase of lean mass in later gestation, either in the fetus or the preterm infant; this relationship is direct and linear. Faster growth rates in earlier gestation require more amino acids and protein than the late preterm or term infant. Protein synthesis and accretion also require sufficient energy, but above ∼120 kcal/kg/day, energy is largely diverted to fat production but not lean mass growth. Optimal IV amino acid solutions remain to be developed, and mature maternal milk and donor human milk require protein supplements to achieve appropriate protein balance and growth. Additional supplements of growth factors might augment increased protein intakes and fortifiers. While excess amino acid and/or protein intakes do not promote growth or development and might even be harmful, providing less than the amounts required guarantees poorer outcomes and should be avoided.