Effect of changes in a food frequency questionnaire: comparing data from two national dietary survey instruments among 12-month-old infants

BACKGROUND National dietary surveys among Norwegian 12-months olds have been conducted twice: in 1999 and 2007. At both time-points diet were assessed by a semi-quantitative food frequency questionnaire (SFFQ) (the SFFQ-1999 and the SFFQ-2007). Modifications in the SFFQ-2007 compared to the SFFQ-1999 have been made; therefore, the objective of the present study has been to explore the comparability of the data obtained by the two questionnaires. Moreover, reliability of maternal recall of infant feeding practices was assessed. METHODS Three hundred Norwegian infants born in April 2007 were invited to participate by completing both the SFFQ-1999 and the SFFQ-2007. An invitation letter and one of two questionnaires were sent by mail to the mother/parents about two weeks before the child turned 12 months of age. The study had a cross-over design where half of the sample received the SFFQ-1999 first and then about 2-3 weeks later they received the SFFQ-2007. The second half received the SFFQ-2007 first, and then 2-3 weeks later they received the SFFQ-1999. RESULTS Ninety three participants completed both questionnaires (SFFQ-1999 and SFFQ-2007). For nutrients, the largest significant differences between the questionnaires were found for intake of vitamin D and added sugar, where added sugar was reported lower and vitamin D was reported higher with the SFFQ-2007 compared to the SFFQ-1999. For food items, lower intake of yoghurt and higher intake of vegetables and fish were observed with the SFFQ-2007 compared to the SFFQ-1999. In addition, reliable answers with regard to breastfeeding status, age for breastfeeding cessation and age for introducing solid foods were found. CONCLUSION There was reasonable comparability between the two questionnaires for most nutrients and foods. The differences between the two questionnaires could mainly be explained by modifications that had occurred over time, where changes in the food composition databases used and especially changes in commercial recipes with regard to baby food products seemed to be of major importance. The differences are important to take into account when interpreting dietary trends among Norwegian 12 month-olds in the period from 1999 to 2007. This study also implies that maternal recall of infant feeding practices is reliable.