Lysine requirement of the enterally fed term infant in the first month of life

Abstract

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.

Phenylalanine requirements of enterally fed term and preterm neonates

“…These amounts are similar to the content of regular Neocate and well above the estimated requirement for term infants of 130 mg/kg per day shown in our earlier IAAO study (13). To keep the amount of nitrogen in the diet constant despite the varying phenylalanine content, molar equivalents of L-alanine were added.…”

“…This study was one of a series that formed a large project to determine the essential amino acid requirement of neonates by using the minimal invasive IAAO method (21) modified for enterally fed neonates and described extensively before (13)(14)(15)22). The method is based on the assumption that amino acids, which are not used for protein synthesis, are preferably oxidized (23).…”

“…Isotopic steady state was reached during the last 45 and 60 min of the [ C]lysine 2HCl infusions, respectively. Samples were analyzed for 13 C abundance in carbon dioxide by using the infrared isotope analysis technique (Helifan; Analytic Fischer Instruments), and the results were reported as the APE.…”

“…The preferred method for determining the amino acid requirement in a vulnerable population is the minimally invasive indicator amino acid oxidation (IAAO) 4 method (12), which we previously validated for use in enterally fed neonates (13,14). The aim of this study was to determine the phenylalanine requirement in the presence of excess tyrosine in healthy, fully enterally fed, term and preterm neonates by using this method.…”

“…Each study day included a 2.5-h (in preterm) or 3-h (in term infants) primed (14-mmol/kg) continuous (9-mmol/kg) infusion of [ 13 C]bicarbonate [sterile, pyrogen free, 99% 13 C atom percent excess (APE); Cambridge Isotopes] to quantify individual carbon dioxide production (24). This was directly followed by a primed (40-mmol/kg) continuous (36-…”