Reproducibility and validity of a food frequency questionnaire

Abstract

OBJECTIVE: Methods to evaluate food consumption still need improvement. A study was conducted to verify the reproducibility and validity of a food frequency questionnaire (FFQ) among overweight adults. METHODS: The study was carried out in a private university in São Paulo, Brazil. The study sample consisted of 146 individuals of both sex with body mass index =25 kg/m² and age between 18 and 60 years old. For reproducibility the FFQ was applied by trained interviewers at two different instances with a mean interval time of 47 days. For validity, data collected from the FFQ were compared with those obtained from the average of 3 different daily records of a 24-hour dietary recall (mean interval time: 15 days). Validity and reproducibility of data on calories and macronutrients consumption was assessed using pondered kappa statistics and intraclass correlation coefficient. RESULTS: A higher variability in the reporting of regular food consumption was seen among obese than overweight individuals. Concerning reproducibility, kappa statistical values varied from 0.23 (carbohydrates and fats) to 0.40 (calories), and intraclass correlation coefficients ranged from 0.28 (protein) to 0.54 (total calories). For FFQ validity, the highest kappa value was 0.25 (calories), and the intraclass correlation coefficient was 0.21 (protein). CONCLUSIONS: Food consumption reports of overweight individuals tend to be underestimated. Despite its limitations, FFQ could be used in epidemiological studies to assess the regular food consumption of overweight individuals.