Development, reproducibility and validity of the food frequency questionnaire in the Poland arm of the Prospective Urban and Rural Epidemiological (PURE) study

BACKGROUND: A food frequency questionnaire (FFQ) is the most commonly used method in large epidemiological studies. The validation of an FFQ is essential for specific populations because foods are culture-dependent. The present study aimed to develop an FFQ and evaluate its validity and reproducibility in estimating the intake of nutrients in urban and rural areas of Poland. METHODS: Adult participants (n = 146) in the Polish arm of the ongoing Prospective Urban and Rural Epidemiological (PURE) study completed FFQs on two occasions, as well as four 24-h dietary recalls (DRs) during a 12-month period. Correlation coefficients (r) and de-attenuated correlation coefficients between dietary recalls and both FFQs were calculated for selected macro- and micronutrients. Agreement between the two methods was evaluated by classification into quartiles and the Bland-Altman method. Reproducibility was assessed by the intra-class correlation coefficient (ICC). RESULTS: The final food list contained 134 food items. For urban participants, FFQ2 generally underestimated energy, protein and fat compared to the FFQ1 and mean of DRs. In rural areas, compared to DRs, both FFQs overestimated energy and macronutrients. For both urban and rural settings, de-attenuated correlation exceeded 0.4 for almost all nutrients and the exact agreement in quartile categorisation was >66%. When assessing repeatability, ICC varied from 0.39-0.63 in an urban setting and 0.19-0.45 in a rural setting. CONCLUSIONS: This 134-item FFQ has good validity and reproducibility in relation to the reference method and can be used to rank individuals based on their macro- and micronutrient intake.