Development and validation of a food frequency questionnaire (FFQ-Porto Alegre) for adolescent, adult and elderly populations from Southern Brazil.

This study assessed the validity of a food frequency questionnaire (FFQ-Porto Alegre), covering 135 food items, in comparison with the average of two consecutive 24-hour dietary recall questionnaires for adolescents, adults, and elderly who were randomly selected from a population-based survey. The Pearson correlation coefficients and cross-classification by quartiles of intake were used. The nutrients were log transformed and energy adjusted. The mean of adjusted de-attenuated correlation coefficient for adolescents was 0.44 and ranged from 0.18 (zinc) to 0.69 (folate) and for adult and elderly participants they were, respectively, 0.42, ranging from 0.16 (iron) to 0.73 (energy) and 0.52, ranging from 0.25 (vitamin E) to 0.84 (energy). The average classification percentage into the same or adjacent quartile for the two methods was 74.6% for adolescents, 74.9% for adults, and 81.2% for the elderly population. The FFQ showed fair relative validity for adolescents and adults, and may be used to study the dietary determinants of obesity and non-transmissible diseases in epidemiological surveys.