Biochemical validation of a self-administered semi-quantitative food-frequency questionnaire

Abstract

The present study is a biochemical validation of a food-frequency questionnaire (FFQ) with optical reading, i.e. containing food portion photographs to help to assess quantities. Forty-four healthy subjects, non-smokers and not taking vitamin supplements, were recruited for the study. After completion of the questionnaire, subjects were asked to keep a 7 d weighed dietary record (7DR). Three 24 h urine samples were collected on 3 different days over the week of food recording for the analysis of urea-N, P and K. On the 4th day of food recording, blood was collected for determination of u-tocopherol, &carotene and ascorbic acid. N, P and K determined in wines and from 7DR were significantly correlated (Spearman rank correlation test), r values being 0.77,0*57 and 0-42 respectively. The correlations with the FFQ were significant only for N (rO45) and P (~0.39). Blood ascorbic acid and p-carotene concentrations correlated with dietary intake when determined from 7DR (both Y 0.44), but not when determined from FFQ. No correlation was found for &ocopherol. The data obtained seem to prove the validity of the FFQ in defining eating patterns in terms of some nutrients, but not vitamins, at least as far as nonsupplemented subjects are concerned. The way in which foods were grouped in the questionnaire could account for these results.Biochemical validation: Food-frequency questionnaire : Food intake.The main purpose of nutritional epidemiology is to study the relationship between an individual's habitual food intake and the risk of disease (Willett, 1990). The food-frequency questionnaire (FFQ) method, notwithstanding some limitations, has become the preferred method in nutritional epidemiology (Willett, 1990), being of low cost and easy to administer. Although the various FFQ have progressively improved their capability of measuring dietary intake, some consistent limits still exist especially due to the lack of quantitative information. In line with this we have developed a self-administered semiquantitative FFQ which contains food portion photographs (Fidanza et al. 1994) to help to assess quantities. Its biochemical validation is reported here.Considering that all the methods used for dietary appraisal of free-living subjects are in general affected by systematic errors (Bingham, 1987), it is impossible to have a valid and reliable reference method for nutrient intake. So to assess the validity the results of one method are compared with another which has a greater acceptance or can be considered more accurate, and until now the weighed record has generally been considered the 'gold standard' (Willett et al. 1985;Block et al. 1990;Hankin et al. 1991). The major limitation available at https://www.cambridge.org/core/terms. https://doi

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