Relative validity of a short food frequency questionnaire for assessing nutrient intake versus three-day weighed diet records in middle-aged Japanese

Background: Validation studies on brief food frequency questionnaires (FFQs) for measuring consumption of macro- and micro-nutrients for the general populace are not fully executed in Japan. Methods: Two hundred and two middle-aged Japanese (73 males and 129 females) in Aichi Prefecture, Japan completed an FFQ and 3 day-weighed diet records (3d-WDRs) in February 2004. We compared intakes of energy and 26 nutrients computed with the FFQ against those with the 3d-WDRs as a reference. Results: Mean daily intakes of selected nutrients determined with the FFQ were generally less than those with 3d-WDRs. The ratios assessed with the FFQ vs. 3d-WDRs (minimum-median-maximum) were distributed from 0.57-0.79-1.09 for males, and 0.61-0.86-1.04 for females. De-attenuated, log-transformed and energy-adjusted Pearson's correlation coefficients between intakes of selected nutrients quantified with both devices were distributed from 0.12-0.45-0.86 and energy-adjusted Spearman's rank correlation coefficients were from 0.13-0.35-0.76, for males. The respective values for females were 0.10-0.38-0.66, and 0.11-0.34-0.47. Median percentages for exact agreement, agreement within adjacent categories, and disagreement according to quartile classification of the energy-adjusted nutrient intakes measured with both methods were 33, 74, and 5 for males, and 35, 76, and 7 for females, respectively. Conclusion: Satisfactorily high relative validity indices of most nutrient intakes computed with the FFQ were attained against those with the 3d-WDRs. The questionnaire therefore appears applicable for categorizing individuals according to consumption of energy and selected nutrients in dietary studies of middle-aged Japanese.