THE VALIDITY OF A SHORT FOOD FREQUENCY QUESTIONNAIRE AND ITS ABILITY TO MEASURE CHANGES IN FOOD-INTAKE - A LONGITUDINAL-STUDY

Background. In studies of health behaviour exploring factors associate d with differences and changes in eating patterns of populations, diet is often measured with short food frequency questionnaires (FFQ). Thi s study examines the validity of a short FFQ by comparing frequencies of food intake from the FFQ to information on food intake obtained by a diet history interview. Methods. Food intake was measured at two sep arate occasions in the same 329 individuals, first in 1987-1988 and 6 years later in 1993-1994. Results. In 1987-1988 the Spearman correlati on coefficients were around r = 0.50 for most foods, with white and da rk ryebread and light bread as extremes on the one hand (r = 0.10, r = 0.23 and r = 0.27, respectively) and coarse bread, fruit and cakes as extremes on the other (r = 0.61, r = 0.60, r = 0.60, respectively). I n general, the correlations were higher at the second data collection in 1993-1994. At both data collections, the mean food intake from the diet history interview increased with increasing frequency category, i ndicating that the questionnaire was able to identify levels of food i ntake correctly. In general, when individual changes in food intake we re assessed during the study period, those who reported a less frequen t intake by the FFQ in 1993-1994 compared with 1987-1988 also had a lo wer mean daily intake according to the diet history information. Concl usion. The short FFQ can quantify food intakes and, is also responsive to changes in food intake over time. Thus the short FFQ can be used t o monitor changes in food patterns at a group level.