Bolus and continuous feeding are equally suitable feeding strategies for preterm neonates. BOL feeding, however, may be preferable.

Although the current recommended methionine intake of 28 mg ⋅ kg(-1) ⋅ d(-1) is within the CIs of our study, the estimated mean requirement is substantially higher. However, most of the infant formulas provide a methionine intake of 49-80 mg ⋅ kg(-1) ⋅ d(-1), which is above the upper CI of our study. This trial was registered at www.trialregister.nl as NTR1610.

Background: Infant nutrition has a major impact on child growth and functional development. Low and high intakes of protein or amino acids could have a detrimental effect. Objective: The objective of the study was to determine the lysine requirement of enterally fed term neonates by using the indicator amino acid oxidation (IAAO) method. L-[1-13 C]phenylalanine was used as an indicator amino acid. Design: Twenty-one neonates were randomly assigned to lysine intakes that ranged from 15 to 240 mg Á kg 21 Á d 21 . Breath, urine, and blood samples were collected at baseline and during the plateau. The mean lysine requirement was determined by using biphasic linear regression crossover analysis on the fraction of 13 CO 2 recovery from L-[1-13 C]phenylalanine oxidation (F 13 CO 2 ) and phenylalanine oxidation rates calculated from the L-[1-13 C]phenylalanine enrichment of urine and plasma. Results: The mean (6SD) phenylalanine flux calculated from urine and plasma L-[1-13 C]phenylalanine enrichment data were 88.3 6 6.9 and 84.5 6 7.4 lmol Á kg 21 Á h 21 , respectively. Graded intakes of lysine had no effect on phenylalanine fluxes. mean requirement was identical to the requirement determined by using phenylalanine oxidation rates in urine and plasma. Conclusions: The mean lysine requirement of enterally fed term neonates was determined by using F 13 CO 2 and phenylalanine oxidation rates calculated from the L-[1-13 C]phenylalanine enrichment of urine and plasma. These methods yielded a similar result of 130 mg lysine Á kg 21 Á d 21 . This study demonstrates that sampling of 13 CO 2 in expired air is sufficient to estimate the lysine requirement by using the IAAO method in infants. This trial was registered at www.trialregister.nl as NTR1610.

In preterm infants, an association between type of feeding (human milk vs infant formula) and time to achieve full enteral feeding or short-term growth was not found. Future prospective trials are needed to verify our results and focus on means to improve tolerance further.

Amino acids play crucial roles as precursors for proteins and neurotransmitters, as transport molecules, and in cell signaling. In this review, we describe the unique functions of the individual amino acids and conclude that the amino acid requirements of parenterally fed neonates are inadequately defined. Parenterally fed neonates are at risk of amino acid deficiency or toxicity because the intestines serve as an important site of metabolism, regulating systemic availability of individual amino acids.