Higher versus lower protein intake in formula-fed low birth weight infants

Dietary protein is needed for normal growth and development. The protein intake required for growth of the low birth weight infant has been estimated by the growth rate of the fetus to be 3.5 to 4 g/kg/day. Controlling the amount of protein given to low birth-weight babies (less than 2.5 kg) fed with formula is important . Too much protein can raise blood urea and amino acid (phenylalanine) levels that may harm neurodevelopment. Too low protein intakes may limit the growth of these infants. The review authors searched the medical literature to identify studies that compared protein intakes: between 3 and 4 g of protein per kg of infant body weight each day versus less than 3.0 g/kg/day or greater than 4.0 g/kg/day by low birth-weight infants fed on formula during their initial hospital stay. Increased protein intake resulted in a greater weight gain of around 2 g/kg/day. Based on increased body incorporation of nitrogen, this was associated with increased lean body mass. The present conclusion was based on five studies changing only the protein content of the formula and supported by three additional studies that also made changes in other nutrients. There was no significant difference in the concentration of plasma phenylalanine between infants fed with high or low protein content formula. The review was limited in the conclusions made since the differences in protein content among comparison groups in some of the individual trials were small and the formulas differed substantially across studies; some studies included healthier and more mature premature infants. The study periods varied from eight days to two years so there was limited information on long-term outcomes. Existing research is not adequate to make specific recommendations regarding formula with protein content that provides more than 4.0 g/kg/day.