Nutritional needs of premature infants: Current Issues

With the major advances in life-support measures, nutrition has become one the most debated issues in the care of very low birth weight infants. Current nutritional recommendations are based on healthy premature infants and are designed to provide postnatal nutrient retention during the “stable-growing” period equivalent to the intrauterine gain of a normal fetus. However, this reference is still a matter of debate, especially in the field of protein and mineral requirements.

Protein requirements recently have been reevaluated, taking into consideration that (1) fetal lean body mass gain and the contribution of protein gain to lean body mass gain appear as more suitable references than does weight gain; (2) an additional protein supply needs to be provided for early catch-up growth, compensating for the cumulative protein deficit developed during the first weeks of life; (3) an increase in the protein-energy ratio is mandatory to improve the lean body mass accretion and to limit fat mass deposition; (4) the fractional nitrogen absorption rate and protein efficiency vary according to the feeding regimens; and (5) recommended dietary protein allowance needs to be adapted for postconceptional age instead of gestational age or birth weight to integrate the dynamic aspect of growth and protein metabolism. Thus recommended intakes for premature infants 26 to 30 weeks postconceptional age are 3.8 to 4.4 g of protein/kg/d with a protein/energy ratio between 3.0 to 3.3 g/100 kcal, according to their relative postnatal growth restrictions and should decrease progressively up to the time of discharge.

After birth, there is a dramatic physiological change in bone metabolism resulting from various factors; abrupt reduction in mineral supply, stimulation of parathyroid hormone secretion, change in hormonal environment, and relative reduction in mechanical stimulation. There is a stimulation of the remodeling process, inducing an increase in endosteal bone resorption and a decrease in physical density. In preterm infants, this process of postnatal bone metabolism adaptation modifies the mineral requirements, with the remodeling stimulation itself providing a part of the mineral requirement necessary for postnatal bone turnover. In extrauterine conditions, the care of premature infants should not necessarily aim to achieve intrauterine calcium accretion rates. Considering long-term appropriate mineralization and the fact that calcium retention between 60 to 90 mg/kg/d suppresses the risk of fracture and clinical symptoms of osteopenia, a mineral intake between 100 to 160 mg/kg/d of highly-absorbed calcium and 60 to 75 mg/kg/d of phosphorus could be recommended.

Abbreviations: BMAD, Bone mineral apparent density, BMC, Bone mineral content, BW, Body weight, Ca, Calcium, LBM, Lean body mass, P, Phosphorus, VLBW, Very low birth weight