Concurrent and construct validity of Mediterranean diet scores as assessed by an FFQ

Objective: The aim of the present study was to assess the concurrent and construct validity of two diet-quality indices, a modified Mediterranean diet score (mMDS) and a Mediterranean-like diet score (MLDS) additionally incorporating unhealthy food choices, as determined by an FFQ. Design: A validation study assessing FFQ intake estimates compared with ten or more unannounced 24 h recalls. Pearson's correlation coefficients, intraclass correlation coefficients (ICC), Bland-Altman plots and the limits of agreement method were used to assess the between-method agreement of scores. Construct validity was shown using associations between nutrient intakes derived from multiple 24 h recalls and the mMDS and MLDS derived from the FFQ. Setting: Gerona, Spain. Subjects: A total of 107 consecutively selected participants from a population-based cross-sectional survey. Results: Pearson's correlations for the energy-adjusted mMDS and MLDS compared with multiple recalls were 0.48 and 0.62, respectively. The average FFQ energy-adjusted mMDS and MLDS were 102% and 98% of the recall-based mMDS and MLDS estimates, respectively. The FFQ under- and overestimated dietary recall estimates of the energy-adjusted MLDS by 28% and 25%, respectively, with slightly wider boundaries for the mMDS (31% and 34%). The ICC, which assesses absolute agreement, was similar to Pearson's correlations (mMDS =0.48 and MLDS = 0.61). The mean differences between methods were similar across the range of average ratings for both scores, indicating the absence of bias. The FFQ-derived mMDS and MLDS correlated in the anticipated directions with intakes of eleven (73.3%) and thirteen of fifteen nutrients (86.7%), respectively. Conclusions: The FFQ provides valid estimates of diet quality as assessed by the mMDS and MLDS.