Nutrient supplies for optimal health in preterm infants.

The most commonly recommended standard for postnatal nutrition of very preterm infants is one that meets the unique nutritional requirements of the growing human fetus and duplicates normal in utero human fetal growth (weight and body composition) and development. Normal fetal nutrition, therefore, may be a useful guide for designing postnatal nutritional strategies in very preterm infants who need to grow and develop outside the uterus. Such information indicates that normal fetal nutrition requires certain nutrients in optimal amounts and certain growth-promoting hormones in response to nutrient supply that together support optimal fetal growth and development; these include oxygen, glucose, lipids, amino acids, and insulin. Interestingly, nutrient restriction and nutrient excess in the fetus, while leading to different phenotypes, produce a similar phenotype in later life characterized as the "metabolic syndrome," consisting of obesity, insulin resistance, diabetes, and cardiovascular disease. After birth, preterm infants--who almost universally are not fed as much as normally growing fetuses receive in nutrient supply via the placenta--also end up with a higher incidence of short stature and a predisposition to the metabolic syndrome, whereas those fed excessive amounts of energy and who develop excessive growth primarily of adipose tissue in early life (rapid, positive crossing of weight-for-length centiles) also develop a higher incidence of the metabolic syndrome. It is clear, therefore, that just the right amount of the essential nutrients is required to produce optimal outcome; this is as true for the preterm infant as it is for the fetus.