Background Several studies suggest that formulas with protein content of 3.0 g/100 kcal do not fully meet the protein needs of preterm very-low-birth-weight infants (VLBWI). This study compared growth, protein-energy status and metabolic status in VLBWI fed either a standard- (Std-Pro: 3.0 g/100 kcal) or high- (Hi-Pro: 3.6 g/100 kcal) protein infant formula.

Methods Once enteral feeding tolerance was established, infants were randomised to be fed either Std-Pro or Hi-Pro formula for a minimum period of 3 weeks. Dietary intake, serum chemistries and growth were closely monitored during the study. Data were analysed on an intention-to-treat basis using a combination of linear mixed model and ANOVA. Results were considered significant at p < 0.05.

Results Sixty-nine infants were enrolled, 51 completed the study. No differences were detected in demographics or energy intakes but protein intake was greater in infants fed Hi-Pro (mean difference: +0.7 g/kg/day, p < 0.0001). No differences were detected in weight gain or body weight but increased protein intake was paralleled by increased blood urea nitrogen (p < 0.001). No differences were detected in weight z-scores but scores in both groups paralleled that in utero. Length z-scores were greater in infants fed Hi-Pro (p < 0.05). As the study progressed, length z-scores did not change in infants fed Hi-Pro, closely paralleling that in utero, but decreased significantly in infants fed Std-Pro (p < 0.0001).

Conclusion A dietary protein intake of 3.6 g/100 kcal meets energy and protein needs while an intake of 3.0 g/100 kcal meets energy but not protein needs in rapidly growing preterm VLBWI.