Relative validity of a dietary interview for assessing infant diet and compliance in a dietary intervention trial

The objective of this study was to assess the relative validity of a dietary interview method for use in an infant population. A dietary interview covering a 1-month period was completed during a study visit at 3 or 6 months of age. It included structured questions and a short food frequency questionnaire (FFQ). The information was compared with data from two 48-h recall interviews conducted during the month previous to the study visit. The agreement between the FFQ and 48-h recalls was analysed as proportion of subjects classified into the same categories of consumption frequency and by the kappa analysis. A total of 100 subjects, at the age of 2–3 months (n = 50) and 5–6 months (n = 50), were included. The kappa values for breastmilk and study formula ranged from 0.82 to 0.95, indicating very good agreement. The agreement for other foods and vitamin D supplementation ranged from fair to very good. We also found a strong correlation for the reported amount of study formula consumed per feeding at 3 months (rs = 0.87, n = 24) and 6 months of age (rs = 0.73, n = 35) between the questionnaire and 48-h recall data. However, the average amount of study formula per feeding was significantly higher when estimated for a 1-month period, compared with a mean calculated from the two 48-h recalls. As a conclusion, the interview was found to be a useful tool for assessing diet and compliance in a dietary intervention for infants.