Reliability and relative validity of an FFQ for nutrients in the Tehran Lipid and Glucose Study

Objective: To describe the relative validity and reliability of the FFQ used for assessing nutrient intakes of participants in the Tehran Lipid and Glucose Study (TLGS). Design: A total of 132 subjects (sixty-one males and seventy-one females) were included in the study. Dietary data were collected monthly by means of twelve 24 h dietary recalls (24hDR). Subjects completed two, 168-item semi-quantitative FFQ. Blood and urine samples were taken every season for measurement of plasma biomarkers and urinary N and K. Results: Mean age and BMI of the participants were 35.5 (SD 16.8) years and 25.5 (SD 5.2) kg/m(2), respectively. The mean energy-adjusted and dattenuated correlation coefficients for overall nutrient intake between the 24hDR and FFQ2 were 0-44 and 0.37 in <= 35-year-olds and >35-year-olds, respectively, and for individual nutrients ranged from 0.24 to 0.71 in men (mean r=0.53) and from 0.11 to 0.60 in women (mean r=0.39). The mean energy-adjusted reliability coefficients varied from 0.48 in <= 35-year-olds to 0.65 in >35-year-olds, and ranged from 0.41 to 0.79 in men (mean r=0.59) and from 0.39 to 0.74 in women (mean r=0.60). The FFQ2 and 24hDR produced exact agreement rates ranging between 39.6% and 68.3% in men and between 39.6% and 54.1% in women. The ranges of questionnaire validity coefficients, with the sample correlation between the questionnaires and biochemical marker as the lower limit and the estimate obtained by the method of triads as the upper limit, were 0.21-0.56 (protein) and 0.37-0.61 (K). Conclusions: The FFQ developed for the TLGS has reasonable relative validity and reliability for nutrient intakes in Tehranian adults.