Validity of a self-administered food frequency questionnaire used in the 5-year follow-up survey of the JPHC Study Cohort I to assess dietary fiber intake: comparison with dietary records.

We examined the validity of a food frequency questionnaire (FFQ) used in the 5-year follow-up survey of the JPHC study for estimation of dietary fiber intake by comparing the intake estimated with dietary records (DR). We developed a food composition table for dietary fiber for the food items included in the FFQ using a substitution method. The Spearman correlation coefficients were slightly higher in crude values (0.48-0.51 in men, 0.40-0.45 in women) than in energy-adjusted values (0.43-0.44 in men, 0.36-0.40 in women). The correlation coefficients of food group-specific dietary fiber (crude) were 0.26 and 0.27 for vegetables, and 0.62 and 0.49 for fruits in men and women, respectively. The mean intakes assessed with the FFQ and DR were not statistically different either for water-soluble or -insoluble fiber in both men and women. However, the fruit fiber assessed with FFQ was significantly over- and the vegetable fiber was underestimated compared with those assessed with DRs. The FFQ can be used for ranking individuals for dietary fiber intakes in epidemiologic studies, despite the difficulty in estimating mean intake.