Background: To the best of our knowledge, no study has tried to develop and validate a multiple-choice food-based FFQ in Iran using weighed dietary records.This study aimed to investigate the validity and reproducibility of a multiple-choice semi-quantitative food frequency questionnaire (SQ-FFQ)in adults living in central Iran.
Methods: Participants attended a large long-term clinical trial were asked to complete three SQ-FFQs by interview, and nine 3-day weighed dietary records (WDRs), over nine months.They provided two blood samples to assess serum calcium, magnesium, zinc, and vitamin C levels.The Pearson and intraclass correlation coefficients (ICC) were calculated to assess reproducibility and validity. The degree of misclassification was explored by using a contingency table of quartiles which is 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.
Results: A total of180 adults aged 48.9±8.4 years completed the study. Compared to WDRs, FFQs overestimated all nutrients intakes except for iron. The median Pearson correlation coefficient was 0.31, 0.44, and 0.38 for FFQ1-FFQ2, FFQ1-FFQ3 and FFQ2-FFQ3, respectively andICC ranged from 0.43 (thiamin) to 0.73 (vitamin D, median: 0.56). The de-attenuated, age, sex, and education adjusted correlation coefficients ranged from 0.01 for vitamin A to 0.40 for vitamin B12 and -0.05 for vitamin A to 0.41 for manganese (median: 0.17 and 0.26) for FFQ1-WDR and FFQ3-WDR, respectively.The medianexact agreement and complete disagreement between FFQ3 and WDRs were 33% and 6%, respectively.The FFQ3validity coefficientsfor vitamin C, calcium, magnesium, and zinc were 0.13, 0.62, 0.89, and 0.66, respectively, using the triads method.
Conclusions: The SQ-FFQseems to be an acceptable tool to assess the long-term dietary intake for future large-scale studies in this population.