Background: In epidemiological studies, the validation of dietary assessment instruments is important to avoid biased associations with outcome measures. Objective: Our objective was to assess the validity of the 134-item food frequency questionnaire (FFQ) used in the Nutrition Environment and Cardiovascular Health (NESCAV) study.

Methods: The FFQ was validated against a 3-day dietary record (DR) on a sample of 29 women. The intraclass correlation coefficient (ICC) and Bland and Altman plots were used to assess absolute agreement, whereas relative agreement was appraised by Spearman’s correlation coefficient and Cohen kappa coefficient based on cross classification of 3-category nutrient intake.

Results: The two methods differed significantly for the majority of micronutrients with FFQ yielding higher intakes than the DR. The bias between the two methods was nonetheless acceptable with an average overestimation by the FFQ of 11% for macronutrients and 29% for micronutrients. Regarding precision, results differed by 48% for micronutrients and 50% for macronutrients. Correlations on energy-adjusted data by the two methods were satisfactory with an average correlation of 0.47 and 16/25 coefficients above 0.40. Only vitamin A and cholesterol showed poor correlations of 0.02 and 0.05, respectively. On average, the correct classification rate in 3 categories was 50.3% and 19/25 kappa coefficients were above 0.20. Poor agreement was found for protein, cholesterol, starch, vitamins A, B12 and E with weighted kappa coefficient less than 0.20.

Conclusion: Although absolute values of dietary intakes were not always accurate, the relationship and agreement between FFQ and DR may be considered as satisfactory. In particular, the FFQ was able to categorize subjects into 3 broad categories of intakes for most nutrients. Results for proteins, cholesterol, starch, vitamins A, E and B12 however ought to be interpreted with caution