Lysine requirement in parenterally fed postsurgical human neonates

Background: The lysine requirement of human neonates receiving parenteral nutrition (PN) has not been determined experimentally. Objective: The objective was to determine the parenteral lysine requirement for human neonates by using the minimally invasive indicator amino acid oxidation technique with L-[1-C-13] phenylalanine as the indicator amino acid. Design: Eleven postsurgical neonates were randomly assigned to 15 lysine intakes ranging from 50 to 260 mg . kg(-1) . d(-1). Breath and urine samples were collected at baseline and at plateau for (CO2)-C-13 ((FCO2)-C-13) and amino acid enrichment, respectively. The mean lysine requirement was determined by applying a 2-phase linear regression crossover analysis to the measured rates of (FCO2)-C-13 release and L-[1-C-13] phenylalanine oxidation. Results: The mean parenteral lysine requirement determined by (FCO2)-C-13 release oxidation was 104.9 mg . kg(-1) . d(-1) (upper and lower CIs: 120.6 and 89.1 mg . kg(-1) . d(-1), respectively). The mean lysine parenteral requirement determined by phenylalanine oxidation was 117.6 mg . kg(-1) . d(-1) (upper and lower CIs: 157.5 and 77.6 mg . kg(-1) . d(-1), respectively). Graded intakes of lysine had no effect on phenylalanine flux. Conclusion: We recommend a mean lysine requirement for the postsurgical PN-fed neonate of 104.9 mg . kg(-1) . d(-1), which is 32-43% of the lysine concentration presently found in commercial PN solutions (246-330 mg . kg(-1) . d(-1)). This trial was registered at clinicaltrials.gov as NCT00779753. Am J Clin Nutr 2010; 91: 958-65.