title: Dietary fiber intake: assessing the degree of agreement between food frequency questionnaires and 4-day food records.
abstract: OBJECTIVE
  To assess the degree of agreement (comparability) between dietary fiber intakes reported on a food frequency questionnaire (FFQ) with 4-day food records (4DFR) and determine whether demographic, behavioral and biological factors influence comparability.
  
  
  METHODS
  At baseline and year one, all participants in the Polyp Prevention Trial (PPT), a multi-center randomized, clinical trial of a low-fat, high fiber, high fruit/vegetable eating plan and recurrence of large bowel adenomatous polyps were instructed in dietary assessment and completed a 106-item FFQ and 4DFR that trained nutritionists reviewed. A random sub-cohort of participants (n = 399) was selected from the intervention and control arms of the PPT for analysis of both FFQ and 4DFR.
  
  
  RESULTS
  Baseline crude and energy-adjusted fiber intakes were significantly higher in the 4DFR than the FFQ (P = 0.001). Using Bland-Altman statistics, the mean difference (FFQ-4DFR) was -0.11 g/MJ; while the limits of agreement were -1.45, 1.23 g/MJ. The mean fiber difference increased with increasing average intake (FFQ + 4DFR)/2, (P = 0.004) for men, but not women (P = 0.10), suggesting that fiber intake was under-estimated in the FFQ, relative to the 4-DFR, for men with low fiber intakes and over-estimated for men with high intakes. Smoking and gender significantly influenced the average intake at baseline, whereas other demographic and behavioral factors did not. Education was significantly associated with average difference in fiber intake at baseline, but not at year 1.
  
  
  CONCLUSIONS
  This study of clinical trial volunteers revealed differences in the ability to comparably report fiber intake across tools by gender, smoking, and education, however participants' repeated training in dietary assessment improved comparability in reporting over time.
authors.affiliation: Division of Cancer Prevention, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-8329, USA.
authors.forename: Tamaro S
authors.initials: TS
authors.lastname: Hudson
authors.forename: Michele R
authors.initials: MR
authors.lastname: Forman
authors.forename: Marie M
authors.initials: MM
authors.lastname: Cantwell
authors.forename: Arthur
authors.initials: A
authors.lastname: Schatzkin
authors.forename: Paul S
authors.initials: PS
authors.lastname: Albert
authors.forename: Elaine
authors.initials: E
authors.lastname: Lanza
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003111:Colonic Polyps / Q000517:prevention & control; D015930:Diet Records; D004043:Dietary Fiber / Q000008:administration & dosage*; D004522:Educational Status; D005247:Feeding Behavior; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015596:Nutrition Assessment; D052756:Nutritional Sciences / Q000193:education; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D017678:Sex Distribution; D011795:Surveys and Questionnaires / Q000592:standards*