Reproducibility and validity of diet quality scores derived from food frequency questionnaires.

BACKGROUND Diet quality scores (DQSs) are frequently used to study diet-disease relationships but the validity of these scores derived from food frequency questionnaires (FFQs) has rarely been evaluated. OBJECTIVE To evaluate the validity and reproducibility of six commonly used DQSs derived from the FFQ, including the Alternate Healthy Eating Index-2010 (AHEI-2010), Dietary Approaches to Stop Hypertension (DASH) score, alternative Mediterranean Diet score (AMED), and three plant-based diet indices (overall, healthful, and unhealthful). DESIGN This analysis included 1,394 participants from the Men's (n = 652) and Women's (n = 742) Lifestyle Validation Studies. Participants completed a 152-item FFQ at the beginning of the study and one year later, and completed two weighed 7-day dietary records (7DDRs) and donated two blood samples six-month apart between FFQ assessments. The reproducibility of the FFQs was evaluated by rank intraclass correlation coefficients (ICC). The validity was assessed by comparing FFQ-derived DQSs to those from the average of two 7DDRs using Spearman rank correlation coefficients deattenuated for random measurement error in the 7DDRs (rs). Further, we calculated the correlations between DQSs and plasma biomarkers of diet including fatty acids, folate, carotenoids, retinol, and alpha-and gamma-tocopherol. RESULTS Six FFQ derived DQSs demonstrated moderate to high reproducibility (energy-adjusted ICCs = 0.61 to 0.84) and validity (energy-adjusted, deattenuated rs = 0.56 to 0.80) in both men and women. We consistently observed expected correlations between FFQ derived DQSs with plasma fatty acids, including long chain N-3 and trans fatty acids, most carotenoids, and gamma-tocopherol (rs>0.2). CONCLUSIONS Our study demonstrates the validity of the FFQ to evaluate overall diet quality using six commonly used DQSs. In addition, these DQSs have qualitatively demonstrated biological relevance as indicated by their correlations with circulating biomarkers.