Validity and reproducibility of a Food Frequency Questionnaire for German descendants living in Brazil

Abstract

Objective This study evaluated reproducibility, relative validity, using a 24-hour recall questionnaire as a reference standard, and estimated calibration factors for a food frequency questionnaire adapted for use with German descendants living in Brazil. Methods The target population consisted of 50 volunteers, of both genders, aged over 20 years, living in a German colonization city in southern Brazil. The food frequency questionnaire was applied twice, in the first and third months of the investigation. During this period, three 24-hour recalls were applied, with an interval of one month between them. Reproducibility was estimated by the intraclass correlation coefficient. Validity was tested by the intraclass correlation coefficient, weighted kappa test and Bland-Altman method. Calibration factors were estimated using linear regression. Results Among the food frequency questionnaires, there was a strong correlation for energy and most of the nutrients corrected for energy. There was a weak correlation between a food frequency questionnaire and a 24-hour dietary recall. However, the exact concordance in the categorization in tertiles among the instruments ranged from 28% (vitamin A) to 52% (fiber and potassium). Gross values of the food frequency questionnaire were reduced with the calibration and approached the consumption data estimated by the 24-hour dietary recall. Conclusions The food frequency questionnaire showed good reproducibility, however, weak correlation with the 24-hour dietary recall. The calibration of the data obtained by the food frequency questionnaire brought them closer to the reference method.