Cyst(e)ine requirements in enterally fed very low birth weight preterm infants

OBJECTIVE. Optimal nutrition is of utmost importance for the preterm infant's later health and developmental outcome. Amino acid requirements for preterm infants differ from those for term and older Infants, because growth rates differ. Some nonessential amino acids, however, cannot be sufficiently synthesized endog-enously. Cyst(e)ine is supposed to be such a conditionally essential amino acid in preterm infants. The objective of this study was to determine, at 32 and 35 weeks' postmenstrual age, cyst(e)ine requirements in fully enterally fed very low birth weight preterm infants with gestational ages of <29 weeks. METHODS. Infants were randomly assigned to 1 of the 5 graded cystine test diets that contained generous amounts of methionine. Cyst(e)ine requirement was determined with the indicator amino acid oxidation technique ([I-13C]phenylaIanlne) after 24-hour adaptation. RESULTS.Fractional [I13-CJphenylalanine oxidation was established in 47 very low birth weight preterm infants (mean gestational age: 28 weeks ± 1 week SD; birth weight: 1.07 kg ± 0.21 kg SD). Increase in dietary cyst(e)ine intake did not result in a decrease in fractional [l-13,CJphenylalanine oxidation. CONCLUSIONS.These data do not support the hypothesis that endogenous cyst(e)ine synthesis is limited in very low birth weight preterm infants with gestational ages of <29 weeks, both at 32 and 35 weeks postmenstrual age. It is safe to conclude that cyst(e)ine requirement is <I8 mg/kg per day in enterally fed very low birth weight preterm infants who are older than 32 weeks' postmenstrual age and whose methionine intake is adequate. Therefore, cyst(e)ine is probably not a conditionally essential amino acid in these infants. Copyrigh

Branched-chain amino acid requirements for enterally fed term neonates in the first month of life

Background: Knowledge of essential amino acid requirements in infants is important because excessive intake of protein can lead to increased long-term morbidity such as obesity. A deficient intake may lead to suboptimal growth and impaired neurodevelopment. The current recommended branched-chain amino acid requirements in infants aged 0-1 mo are based on the amino acid content of human milk. Objective: We quantified the requirements for isoleucine, leucine, and valine for term neonates by using the indicator amino acid oxidation method with [1-13C]phenylalanine as the indicator. Design: Fully enterally fed term infants received randomly graded amounts of isoleucine (5-216 mg · kg-1 · d-1), leucine (5-370 mg · kg -1 · d-1), or valine (5-236 mg · kg -1 · d-1) as part of an elemental formula. Data are expressed as means ± SDs. Results: Eighty-three Asian, term neonates (mean ± SD birth weight: 3.3 ± 0.4 kg; gestational age: 39.4 ± 1.3 wk) were studied at a postnatal age of 13 ± 5 d. Mean requirements for isoleucine, leucine, and valine (measured in boys only) were 105 mg · kg-1 · d-1 (r2 = 0.61, P < 0.001), 140 mg · kg-1 · d-1 (r 2 = 0.26, P < 0.01), and 110 mg · kg-1 · d-1 (r2 = 0.35, P = 0.001), respectively. Conclusions: Current human milk-based recommendations for isoleucine and valine in term infants aged 0-1 mo are correct. However, the current recommendation for leucine (166 mg · kg-1 · d-1) is higher than the mean requirement of 140 mg · kg-1 · d-1 that we determined in this study. This trial was registered at www.trialregister. nl as NTR1610