Effect of changes in an FFQ: comparing data from two national dietary survey instruments among 2-year-olds

In the interpretation of dietary trends, it is important to consider the potential effect of modifications in the dietary assessment method. Therefore, our objective was to explore the comparability of data obtained at two time points by a semi-quantitative FFQ (SFFQ) which has had slight modifications over time. In the national dietary surveys among Norwegian 2-year-olds, diet was assessed by an SFFQ which underwent modifications between the 1999 survey and the 2007 survey. In the present study, fifty-nine families with a 2-year-old child participated by completing both the SFFQ in a crossover design within a month's time. With regard to the reported intake of energy and nutrients, the largest significant differences observed between the two questionnaires were for carbohydrates and added sugar. According to intake of food groups, significant differences were observed for five out of sixteen food groups. Spearman's correlation coefficients for energy, nutrients and food groups ranged from 0.43 (Ca) to 0.85 (soft drinks). Most Bland-Altman plots indicated broad limits of agreement. The differences between the two questionnaires can be explained by changes in the questionnaires, changes in the food composition databases used and random variation. Comparing differences between the questionnaires by maternal educational level, number of children and type of day care revealed minor differences. In conclusion, this study showed that at the group level there was reasonable comparability between the two questionnaires, except for carbohydrates, added sugar and some food groups. Moreover, there were moderate to high correlations for energy, nutrients and food groups.