Nutritional Requirements of Low Birth weight Infants

Because of the rapid rate of anabolic processes and brain growth, no patient faces a more critical need for optimal nutrition than the low birthweight (LBW) infant. Nutritional requirements of these infants, however, remain unclear. Much of the controversy centers on the question: How fast should they grow? The Committee on Nutrition of the American Academy of Pediatrics (1) has stated that: "The optimal diet for the low birthweight infant may be defined as one that supports a rate of growth approximating that of the third trimester of intra-uterine life without imposing stress on the developing metabolic and excretory systems." Employing a factorial method, Ziegler et al. (2) summed the tissue accretion of nutrients with estimates of urinary and dermal losses and the extent of absorption to derive theoretical requirements of nutrients for infants of varying gestational ages. These calculations suggest that human milk and many formulas do not provide sufficient quantities of protein and certain minerals to support intrauterine rates of growth. In contrast, Raiha et al. (3,4) reported that preterm infants fed pooled human milk have less metabolic acidosis, low blood urea nitrogen and ammonia values, and fewer amino acid aberrations than infants fed high-protein formulas. These investigators contend that a growth rate and an accumulation of nutrients more important than those provided by human milk are not necessarily desirable. More recent studies conclude, however, that pooled breast milk is not ideal for LBW infants, since this feeding results in poorer fat absorption, a less desirable nutritional status, and slower weight gain when compared to fresh own-mother's milk or formulas adapted for LBW infants (5-7). In this chapter, we suggest some guidelines concerning the nutritional requirements of LBW infants in the light of results of metabolic balance studies carried out by us in more than 100 preterm infants during the last 10 years.