Validation and reproducibility of a novel flavonoid food frequency dietary assessment tool (Flav-Q) against multiple 24-h recalls across 12 months

Purpose: Measurement of dietary flavonoid intake requires a reliable tool. This study validated and evaluated the reproducibility of a 23-item shortened flavonoid food frequency questionnaire (FLAV-Q), derived from the 96-item Kent & Charlton Flavonoid specific-FFQ. Methods: The FLAV-Q was validated against an average of repeated 24-h dietary recalls using Intake-24 completed quarterly over the period of a year that were adjusted to represent habitual intake by applying the multiple source method (MSM) in 80 Australian adults. FLAV-Q validity was estimated using the Wilcoxon signed-rank test, Spearman’s correlation coefficient, Bland-Altman plots, and Cohen’s kappa (κ). Reproducibility was assessed by comparing the FLAV-Qs at four timepoints. Results: FLAV-Q overestimated total flavonoid intake against habitual intake (443.2 mg/day versus 234.4 mg/day, p < 0.001) and all subclasses except for flavanones. Moderate agreement was detected for total flavonoids (r = 0.66, p < 0.001; κ = 0.45, p < 0.001), flavan-3-ols (r = 0.72, p < 0.001; κ = 0.53, p < 0.001), flavonols (r = 0.55, p < 0.001; κ = 0.40, p < 0.001), flavanones (r = 0.50, p < 0.001; κ = 0.30, p = 0.007) and fair but non-significant agreement for anthocyanins (r = 0.38, p < 0.001; κ = 0.15, p = 0.18) and flavones (r = 0.34, p < 0.001; κ = 0.20, p = 0.07). Bland-Altman plots showed a large bias (Bland-Altman index: 7.5%) for total flavonoid intake. FLAV-Q demonstrated moderate reproducibility across timepoints with mean percentage differences for total flavonoid intake ranging from 22% to 37%. Bland-Altman plots indicated moderate to small bias for reproducibility (Bland-Altman index: 2.5–3.8%). Conclusions: FLAV-Q demonstrates moderate to low validity and reproducibility for total flavonoids and the subclasses. Further validation for absolute intake values is necessary to understand and address the overestimation.