title: Methionine requirement of the enterally fed term infant in the first month of life in the presence of cysteine.
abstract: BACKGROUND
  The essential amino acid methionine can be used for protein synthesis but also serves as a precursor for homocysteine and cysteine.
  
  
  OBJECTIVE
  The objective of this study was to determine the minimal obligatory methionine requirement of infants in the presence of excess cysteine (91 mg ⋅ kg(-1) ⋅ d(-1)) by using the indicator amino acid oxidation (IAAO) method with l-[1-(13)C]phenylalanine as the indicator.
  
  
  METHODS
  Fully enterally fed term infants <1 mo of age were randomly assigned to methionine intakes that ranged from 3 to 59 mg ⋅ kg(-1) ⋅ d(-1) as part of an elemental formula. After 1 d of adaptation to the test diet, [(13)C]bicarbonate and l-[1-(13)C]phenylalanine tracers were given enterally. Breath samples were collected at baseline and during isotopic plateaus. The mean methionine 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)). Data are presented as means ± SDs.
  
  
  RESULTS
  Thirty-three neonates (gestational age: 39 ± 1 wk) were studied at 13 ± 6 d. With increasing methionine intakes, F(13)CO(2) decreased until a methionine intake of 38 mg ⋅ kg(-1) ⋅ d(-1); additional increases in methionine intake did not affect F(13)CO(2). The mean methionine requirement was determined at 38 mg ⋅ kg(-1) ⋅ d(-1), and the upper and lower CIs were 48 and 27 mg ⋅ kg(-1) ⋅ d(-11), respectively (P < 0.0001, r(2) = 0.59).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Pediatrics, Division of Neonatology, Medical Centre-Sophia Children's Hospital, Rotterdam, Netherlands.
authors.forename: Lisha
authors.initials: L
authors.lastname: Huang
authors.forename: Jacomine E
authors.initials: JE
authors.lastname: Hogewind-Schoonenboom
authors.forename: Mariska J A
authors.initials: MJ
authors.lastname: van Dongen
authors.forename: Femke
authors.initials: F
authors.lastname: de Groof
authors.forename: Gardi J
authors.initials: GJ
authors.lastname: Voortman
authors.forename: Henk
authors.initials: H
authors.lastname: Schierbeek
authors.forename: Jos W R
authors.initials: JW
authors.lastname: Twisk
authors.forename: Andras
authors.initials: A
authors.lastname: Vermes
authors.forename: Chao
authors.initials: C
authors.lastname: Chen
authors.forename: Ying
authors.initials: Y
authors.lastname: Huang
authors.forename: Johannes B
authors.initials: JB
authors.lastname: van Goudoever
mesh_terms: D002247:Carbon Isotopes / Q000737:chemistry; D018592:Cross-Over Studies; D003545:Cysteine / Q000008:administration & dosage* / Q000378:metabolism*; D019587:Dietary Supplements; D004305:Dose-Response Relationship, Drug; D004750:Enteral Nutrition / Q000379:methods*; D005260:Female; D006801:Humans; D007227:Infant Nutritional Physiological Phenomena; D007231:Infant, Newborn; D016014:Linear Models; D008297:Male; D008715:Methionine / Q000008:administration & dosage* / Q000378:metabolism*; D009751:Nutritional Requirements; D010084:Oxidation-Reduction
chemical_list: D002247:Carbon Isotopes; D008715:Methionine; D003545:Cysteine