Relative Validity and Reproducibility of a Semi-quantitative Food Frequency Questionnaire among Urban Iranians

The contribution of dietary factors to the development and prevention of non-communicable diseases is being increasingly recognized, and worldwide, the concern about chronic diseases is growing rapidly. There is a lack of a comprehensive food frequency questionnaire (FFQ) encompassing all kinds of foods for Iranians. This cross-sectional study aims to describe the relative validity and reproducibility of the FFQ used for assessing nutrient intakes of Iranian urban population. One hundred thirteen subjects aged 20–69 years from five major cities of Iran participated in this study. The dietary intake was assessed by a semi-quantitative FFQ involving 160 Iranian food items. The participants were asked to complete two FFQs (at the first and fourth months of the study) and three-day food records every month. Two blood and 24-h urine samples were collected at fifth and sixth months. The highest correlation coefficient in all FFQs was for fat (r = 0.669; p < 0.001) and the lowest for fiber (r = 0.331; p = 0.001). The Pearson correlation coefficients between nutrient intake estimated by the average of the two FFQs and the average of the three-day food records ranged from 0.03 to 0.27. The Pearson correlation coefficients between serum and urine biomarkers and nutrient intake estimated by the average of the two FFQs ranged from −0.34 to 0.47. Bland and Altman analyses showed fairly good agreement between the average of the FFQs and three-day food records for energy, fat, and potassium intakes. The obtained results indicate a reasonable validity of the FFQ considering the energy, fat, and potassium intake evaluation and good reproducibility over a 6- month period.