On the importance of using multiple methods of dietary assessment.

Background: Plasma carotenoid concentrations reflect intake of vegetables and fruits, the major food sources of these compounds. This study compared the ability of 2 measures of dietary intake (24-hour diet recalls and food frequency questionnaires [FFQs]) to corroborate plasma carotenoid concentrations in a subset of women participating in a diet intervention trial.

Methods: Plasma carotenoid concentrations and dietary intakes, estimated from 24-hour diet recalls and FFQs, were examined at baseline and 1 year later in a subset of 395 study participants (197 intervention and 198 comparison group). We used longitudinal models to examine associations between estimated intakes and plasma carotenoid concentrations. These analyses were stratified by study group and adjusted for body mass index (BMI), plasma cholesterol concentration, and total energy intake. We conducted simulations to compare mean-squared errors of prediction of each assessment method.

Results: In mixed-effects models, the estimated carotenoid intakes from both dietary assessment methods were strongly associated with plasma concentrations of alpha-carotene, beta-carotene, and lutein. Furthermore, modeling the 2 sources of intake information as joint predictors reduced the prediction error.

Conclusion: These findings underscore the importance of using multiple measures of dietary assessment in studies examining diet-disease associations.