37 Dietary proteins and IGF I levels in preterm infants 2 (65). A high protein intake in the in-hospital as well as in the post discharge period seems to decrease fat mass and increase lean mass up to 6 months corrected age (67-69). Whether this trend persists into childhood is not known. Using bone transmission time Scattolin and colleagues found protein intake to positively correlate with bone mineral status at 36 weeks postmenstrual age (66). However Fewtrell was unable to correlate protein intake in infancy with peak bone mass or bone turnover in young adulthood (41). Thus a persisting beneficial effect of early protein intake on growth and body composition in later life has not yet been confirmed. Even though protein is vital to optimize growth, its relation to other nutrient components and the administration of specific amino acids are equally important. Indeed Mcleod and colleagues demonstrated that an increased protein/energy ratio reduced adipose tissue accretion as compared to muscle accretion. Surely energy from another source than protein itself is necessary for net protein gain. However when non-protein caloric intake surpasses 60 kcal/kg/day, protein intake itself is the primary determinant of protein gain. Nevertheless it should be questioned to which level the protein/energy ratio should be increased. The ESPGHAN committee on nutrition recommends a ratio of 3.2 to 4.1 g protein/100 kcal (53). Yet there is a need of supportive evidence as to which ratio should be maintained at specific points in time. Several studies found that when preterm infants were on complete enteral nutrition increasing the protein/energy ratio above 3 g protein/ 100 kcal did not improve fat free mass accretion compared to a ratio of 2.7-2.8 g protein/100 kcal (67, 70). To our knowledge studies conducted so far have not assessed the effects on body composition of various protein/energy ratios in the first two weeks of life. Because preterm infants have limited ability to synthesize certain non-essential amino acids those amino acids become conditionally essential. Some have proposed that the addition of these so called semi-essential amino acids to the diet of preterm infants will improve growth. Cysteine for example, has been implied to be one of the key factors which potentiate the trophic effect of high protein diets (71). The role of dietary proteins in neurodevelopment During hospitalisation increased protein intake improves head growth in preterm infants (72, 73). Even so total energy and lipid intake also have been positively correlated with head growth (73, 74). Nonetheless Hansen-Pupp and colleagues could not associate protein and caloric intake with brain volumes (43) and in several studies protein-enriched nutrition failed to improve neurodevelopmental outcome up to 18 months corrected age (59, 72, 75, 76). Macro- and microstructural brain analyses could not be correlated to intake of protein or other nutritional components either (46). Yet, two studies by Stephens et al. and Cormack et al.
RkJQdWJsaXNoZXIy MTk4NDMw