Abstract
Newborn humans and animals grow at very rapid rates because they use very efficiently the protein that they eat to increase body protein mass. This high efficiency of protein deposition in neonates is largely due to their ability to markedly increase the amount of protein synthesized in their muscles when they eat. This enhanced stimulation of muscle protein synthesis after eating is mediated by the rise in the hormone, insulin, and the rise in amino acids, which are the building blocks of protein. Intracellular signaling components that respond to insulin and amino acids have been identified, and these have been shown to be involved in the feeding-induced stimulation of protein synthesis in the skeletal muscle of the neonate. The enhanced activation of these intracellular signaling components in neonatal muscle contributes to the high rate of muscle protein synthesis and rapid gain in skeletal muscle mass in newborns.