Validity and Reproducibility of a Semiquantitative Multiple-Choice Food Frequency Questionnaire in Iranian Adults

Previous multiple-choice food-based food frequency questionnaires (FFQs) were not validated against weighed dietary records (WDRs) in Iran. This study investigated the validity and reproducibility of a multiple-choice semi-quantitative food frequency questionnaire (SQ-FFQ) in adults living in central Iran. Patients with diabetes and their spouses were asked to complete 3 SQ-FFQs by interview, and nine 3-day WDRs, over 9 months. They provided 2 blood samples to assess serum calcium, magnesium, zinc, and vitamin C levels. The Pearson and intraclass correlation coefficients were calculated to assess reproducibility and validity. The degree of misclassification was explored using a contingency table of quartiles which compare the information between third FFQ and WDRs. The method of triads was incorporated to assess validity coefficients between estimated intakes using third FFQ, WDRs, and biochemical markers and assumed true intakes. A total of 180 participants aged 48.9 ± 8.4 years completed the study. Compared to WDRs, FFQs overestimated all nutrient intakes except for iron. The median intraclass correlation between FFQs was 0.56. The median de-attenuated, age, sex, and education adjusted partial correlation coefficients for validity were 0.17 and 0.26 for FFQ1-WDRs and FFQ3-WDRs, respectively. The FFQ3 validity coefficients for vitamin C, calcium, magnesium, and zinc were 0.13, 0.62, 0.89, and 0.66, respectively, using the triads method. The median exact agreement and complete disagreement between FFQ3 and WDRs were 33% and 6%, respectively. The SQ-FFQ seems to be an acceptable tool to assess the long-term dietary intake for future large-scale studies in this population.