In the present investigation, we evaluated the validity of using a 200-item semiquantitative FFQ in a large prospective study in western Greece. An important consideration when interpreting the results is the fact that a great percentage of the food groups and food items that were statistically compared confirmed the validity of our questionnaire. To assess the relative validity, we chose the 24-hour-recall method for the forthcoming 7 days as the reference method. Because the interviews with the children were conducted at school, and the phone interviews were carried out with the parents after they had been previously notified and interview times had been set, the response rate was high. Only two of the parents refused to participate because of time limitations. Taking into consideration the age group of our sample, as well as the fact that children in this age group have not completely developed the ability to think abstractly and calculate their average food intake , we interviewed fourth- and fifth-grade children with great attention. To avoid errors in estimation of the children's food consumption, the interviewer used photographs of food portions and tried to clarify the real food intake. Special attention was given to determine the maturity level of each child and its effect on the child's answers.
The eating patterns selected for this study and the methodological approaches chosen to analyze the dietary data were based on an extensive review of the literature [16–20], food consumption patterns [21, 22], total gram amount of food/beverages consumed by meal, total number of snack periods, and total eating episodes [23–25]. A comparison of the results revealed very good agreement for milk. Good agreement was determined for several food groups (fish food, pies, delicatessen, and dairy), as well as for several food items (cheese, legumes, and pizza). The children's and parents' questionnaire responses relating to milk consumption were in almost perfect agreement – most likely because milk is a daily source of nutrients in childhood and is consumed at standard time frames within a day (e.g., morning, afternoon, and evening). Consequently, it was easier to calculate the frequency and the quantity of milk consumption. Accordingly, we could explain the good agreement found for several food groups (fish food, pies, delicatessen, and dairy) and for several food items (cheese, legumes, and pizza). It is well known that Greek nutritional culture primarily consists of fish food, dairy, cheese, and legumes . We noticed that the children and their parents reported the same frequencies for legumes and fish food because most Greeks have standard days for the consumption of these food items. Legumes are usually consumed on Wednesdays and Fridays because of fasting, whereas fish is traditionally consumed on Saturdays. Based on these findings, we concluded that the strong agreement found for some food items was related to the traditional weekly nutrition routine of Greeks. The calculation of frequency consumption revealed high accuracy.
Of particular interest was the poor agreement between the children's and the parents' questionnaire responses regarding the consumption of several food items – specifically, fruit, sweets, sandwiches, and potatoes. The statistical analysis showed that although poor agreement was attained for these food items, the parents had occasionally underestimated the children's consumption of sweets, sandwiches, and potatoes, and overestimated the consumption of fruit. In our opinion, the parents' overestimation/underestimation of their children's consumption of certain foods may be related to the fact that parents may not (consciously or subconsciously) want to divulge their children's nutritional choices. Their responses, which suggested that their children possess a balanced diet) may be based on wishful thinking. We suspect that some parents had a tendency to overlook the quantity and the frequency of many food items that their children consumed.
Based on our findings, we feel confident in the appropriateness of this questionnaire in examining the food consumption of the Greek student population and in ranking the subjects according to food group intake. However, findings of similar studies have shown that dietary intake cannot be estimated without the possibility of error and that great attention should be given when selecting and employing the most appropriate dietary data collection method as well as the analytical and statistical methods [27–32].