PURPOSE - Foods consumed near the time of food frequency questionnaire (FFQ) administration may prime the memory, such that FFQ responses emphasize recently consumed foods. This study investigates the effect of season of FFQ administration, a proxy for the recent diet, on FFQ responses.
METHODS - FFQ data from 74,958 Shanghai Women's Health Study (SWHS) subjects were compared with FFQ data from these subjects by season of FFQ administration (i.e., winter, spring, summer, and fall). All analyses were adjusted for age, BMI, and energy intake. Furthermore, quintile categories derived from all study subjects were compared with categories derived from the distribution of subjects recruited in the same season.
RESULTS - Compared with the study group as a whole, subjects completing the FFQ in winter reported higher intakes of meat (2.1%), vegetable (3.9%), fish (3.1%), and soy foods (4.1%), but lower fruit (- 3.9%) intake. Subjects completing the FFQ in summer reported lower than average meat (- 2.0%), vegetable (- 3.2%), fish (- 2.3%), and soy food (- 4.6%) intakes, but greater fruit intake (0.9%). Completion of the FFQ in spring and fall usually led to intermediate differences from the group average, although fruit intake was 5.9% higher among subjects completing the FFQ in the fall. Variations across macronutrients and micronutrients by season of FFQ administration were smaller. If seasonal FFQ reporting is ignored, up to 13% of subjects would be classified to a different diet intake exposure category. However, reclassification was always to an adjacent category.
CONCLUSIONS - FFQ responses varied with season of FFQ administration, consistent with theory that current diet intake influences reporting of habitual past diet intake. However, season of FFQ administration did not alter dietary exposure category assignments sufficiently to effect interpretation of most epidemiologic studies.