Academy of Medical Sciences of I.R. Iran Archives of Iranian Medicine 1029-2977 28 9 2025 09 01 Relative Validity and Reproducibility of a Semi-quantitative Food Frequency Questionnaire to Assess Nutrient Intakes of PERSIAN Cohort Participants: Comparisons to 24-Hour Dietary Recalls and Selected Biomarkers 485 497 10.34172/aim.34573 EN Sareh Eghtesad https://orcid.org/0000-0001-5357-8867 Maryam Sharafkhah Azita Hekmatdoost Alireza Ostadrahimi Mojtaba Farjam Alireza Vakilian Yahya Pasdar Motahareh Kheradmand Fariba Shahraki-Sanavi Amir Houshang Mehrparvar Amaneh Shayanrad Zahra Mohammadi Monireh Sadat Seyyedsalehi Walter C. Willett Reza Malekzadeh Hossein Poustchi https://orcid.org/0000-0003-4566-3628 Journal Article 10.34172/aim.34573 2025 05 26 2025 08 20 Background: Food frequency questionnaires (FFQs) are widely used in epidemiologic studies to assess the dietary intake of individuals. In this study, we evaluated the validity and reproducibility of the FFQ used in the Prospective Epidemiological Research Studies in IrAN (PERSIAN) for assessing nutrient intakes. Methods: Individuals (n=978) from seven PERSIAN cohort centers participated in this study; an initial FFQ was completed for each person upon enrollment (FFQ1), followed by two 24-hour dietary recalls (24HR) each month, for twelve months, and finally, another FFQ at the end of the study (FFQ2). Serum and 24-hour urine (24H-U) samples were also collected each season, and selected biomarkers were measured. To assess validity, correlation coefficients between the 24HRs and the FFQs were obtained. The triad method was used to compare the biomarkers to the FFQs. Correlations between FFQ1 and FFQ2 were evaluated to assess the reproducibility of the questionnaire. Results: Correlations obtained for energy and macronutrients, in comparing FFQ1 and FFQ2 to the 24HRs were 0.57,0.63 (energy), 0.56,0.62 (protein), 0.51,0.55 (lipids) and 0.42,0.51 (carbohydrates), respectively. Moderate (0.4‒0.6) and high (>0.6) correlations were seen for micronutrients, with only vitamins B6 and B12 being poorly correlated (<0.4). Validity coefficients obtained for urinary protein and sodium, as well as serum folate and selected fatty acids were acceptably above 0.4. Reproducibility correlations ranged from 0.18 (alpha-linoleic acid) to 0.78 (selenium), with 19 of the 30 evaluated nutrients showing high and 2 showing poor correlations. Conclusion: Overall, the PERSIAN Cohort FFQ is acceptable to rank individuals based on their nutrient intakes.