title: Cyst(e)ine requirements in enterally fed very low birth weight preterm infants.
abstract: 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 endogenously. 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 ([1-(13)C]phenylalanine) after 24-hour adaptation.
  
  
  RESULTS
  Fractional [1-(13)C]phenylalanine 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 [1-(13)C]phenylalanine 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 <18 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.
authors.affiliation: Erasmus MC-Sophia Children's Hospital, Department of Pediatrics, Division of Neonatology, Dr Molewaterplein 60, 3015 GJ, Rotterdam, The Netherlands.
authors.forename: Maaike A
authors.initials: MA
authors.lastname: Riedijk
authors.forename: Gardi
authors.initials: G
authors.lastname: Voortman
authors.forename: Ron H T
authors.initials: RH
authors.lastname: van Beek
authors.forename: Martin G A
authors.initials: MG
authors.lastname: Baartmans
authors.forename: Leontien S
authors.initials: LS
authors.lastname: Wafelman
authors.forename: Johannes B
authors.initials: JB
authors.lastname: van Goudoever
mesh_terms: D000704:Analysis of Variance; D001835:Body Weight; D003545:Cysteine / Q000008:administration & dosage*; D004750:Enteral Nutrition / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007231:Infant, Newborn; D019102:Infant, Very Low Birth Weight; D008297:Male; D009751:Nutritional Requirements; D018529:Nutritional Support; D011336:Probability; D012044:Regression Analysis; D016896:Treatment Outcome; D015430:Weight Gain
chemical_list: D003545:Cysteine