Validation of food frequency questionnaire for assessing dietary macronutrients and calcium intake in Italian children and adolescents

OBJECTIVES: To validate a food frequency questionnaire to determine calcium and macronutrient intake in healthy children and adolescents. MATERIALS AND METHODS: The questionnaire consisted of 16 main food groups containing the main foods composing the diet of Italian children, a total of 136 items and 23 questions about food habits, supplements and servings. Color photographs to identify serving size were included. The questionnaire was validated by comparing it with the 7-day weighed record method in 37 healthy volunteers in two different age groups: children aged 6 - 10 years (n = 18) and adolescents aged 16 - 20 years (n = 19). RESULTS: The food frequency questionnaire seemed to overestimate the nutrient intake when compared with 7-day weighed records; however the two methods were highly correlated for all the nutrients considered. The range of Pearson's correlations between energy and nutrient intake (protein, fat, carbohydrates and calcium) determined from food frequency questionnaire and 7-day weighed record were 0.5-0.6 in children and 0.5-0.8 in young adults. Agreement between the two methods in classifying relative intakes was examined by determining the frequency of similar classification into terciles. Two thirds of the subjects were correctly classified for most nutrients, with a very low (2% to 5%) percentage of grossly misclassifications. DISCUSSION: The food frequency questionnaire has proved adequate to rank a pediatric population in terms of calcium and macronutrient intakes. The ranking of subjects is extremely useful for epidemiologic studies evaluating the relation between nutrient intake and disease.