Validity and reproducibility of a semi-quantitative food frequency questionnaire for Iranian adults

To validate a semi-quantitative food frequency questionnaire (SFFQ) and assess the dietary intake of Iranian adults.

This study was conducted among 113 healthy adults in Iran. We administered twelve 24-hour dietary recalls (24DRs) during a year as a reference method. The 165-item SFFQ was administered twice, along with the first and last 24DRs. To examine validity and reproducibility of SFFQ, the correlation coefficients (r) and de-attenuated correlation coefficients and intra-class correlation coefficient (ICC) between 24DRs and SFFQ were calculated. The Bland-Altman method was used to assess agreement between the two methods.

De-attenuated correlations varied from 0.42 (polyunsaturated fatty acids) to 0.62 (energy) (all P < .001) for nutrients and from 0.48 (oils and fats) to 0.65 (sweets) for food groups (all P < .05). We found reasonable reproducibility of SFFQ for both nutrients and food groups. ICC (95%CI) varied from 0.47 (0.15-0.74) for saturated fatty acids to 0.64 (0.47-0.76) for energy and from 0.43 (0.15-0.62) for oils and fats to 0.58 for grains (0.31-0.69). According to the Bland-Altman plots, we observed an acceptable level of agreement between the two methods.

We found reasonable relative validity and acceptable reproducibility of SFFQ. This SFFQ can be used to classify individuals based on their dietary intake in our population.