title: Reproducibility and validity of an FFQ to assess usual intake of methyl-group donors.
abstract: OBJECTIVE
  To develop and validate a novel FFQ to assess the daily intake of four methyl-group donors (methionine, choline, betaine and folate).
  
  
  METHODS
  The relative validity of the FFQ was assessed by comparison with 7 d estimated diet records (n 80) and its reproducibility was evaluated by repeated administrations 6 weeks apart (n 92). Paired Student t tests were used to compare group means and de-attenuated intra-class correlations to investigate the ability of the FFQ to rank individuals according to their methyl-group donor intake. De-attenuated intra-class correlation coefficients were calculated between the test and reference method for methionine, choline, betaine, folate and the sum of methyl-group donors. The weighted kappa (κ w) was calculated as a measure of tertile agreement.
  
  
  METHODS
  Flanders, Belgium.
  
  
  METHODS
  The FFQ was validated among Flemish women of reproductive age (18-35 years).
  
  
  RESULTS
  The questionnaire had an acceptable ranking ability (r=0·32-0·68; κ w=0·10-0·35), but overestimated the daily intake of folate (280·6 μg v. 212·0 μg) and betaine (179·1 mg v. 147·0 mg) compared with the 7 d estimated diet record. Cross-classification analysis indicated that 20 % (choline) of the participants were grossly misclassified in the validation study. The correlation between repeated administrations was good (r=0·62-0·83) with a maximal misclassification of 7 % for betaine (κ w=0·44-0·66).
  
  
  CONCLUSIONS
  These results indicate that this newly developed FFQ is a reliable instrument with acceptable validity for ranking individuals according to methyl-group donor intake (except for a poor agreement for choline (κ w=0·10) and a fair ranking ability for betaine (r=0·32)) in Flemish women of reproductive age.
authors.affiliation: 1KU Leuven,Department of Public Health and Primary Care,Centre Environment & Health,Kapucijnenvoer 35blok Dbox 7001,3000 Leuven,Belgium.
authors.forename: Sara
authors.initials: S
authors.lastname: Pauwels
authors.affiliation: 1KU Leuven,Department of Public Health and Primary Care,Centre Environment & Health,Kapucijnenvoer 35blok Dbox 7001,3000 Leuven,Belgium.
authors.forename: Ine
authors.initials: I
authors.lastname: Doperé
authors.affiliation: 3International Agency for Research on Cancer,Dietary Exposure Assessment Group,Lyon,France.
authors.forename: Inge
authors.initials: I
authors.lastname: Huybrechts
authors.affiliation: 1KU Leuven,Department of Public Health and Primary Care,Centre Environment & Health,Kapucijnenvoer 35blok Dbox 7001,3000 Leuven,Belgium.
authors.forename: Lode
authors.initials: L
authors.lastname: Godderis
authors.affiliation: 2Flemish Institute of Technological Research (VITO),Unit Environmental Risk and Health,Mol,Belgium.
authors.forename: Gudrun
authors.initials: G
authors.lastname: Koppen
authors.affiliation: 1KU Leuven,Department of Public Health and Primary Care,Centre Environment & Health,Kapucijnenvoer 35blok Dbox 7001,3000 Leuven,Belgium.
authors.forename: Greet
authors.initials: G
authors.lastname: Vansant
mesh_terms: D000293:Adolescent; D000328:Adult; D001530:Belgium; D001622:Betaine / Q000008:administration & dosage*; D002794:Choline / Q000008:administration & dosage*; D004032:Diet; D004034:Diet Surveys; D005247:Feeding Behavior; D005260:Female; D005492:Folic Acid / Q000008:administration & dosage*; D006801:Humans; D008715:Methionine / Q000008:administration & dosage; D008745:Methylation; D015596:Nutrition Assessment; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires / Q000592:standards*; D055815:Young Adult
chemical_list: D001622:Betaine; D005492:Folic Acid; D008715:Methionine; D002794:Choline
keywords: Dietary assessment; FFQ; Methyl-group donors; Validation