The aim of this research was to observe whether there were any direct associations between the frequency of breakfast and snack consumption and fruit and vegetable intake among 11-, 13- and 15-year-old Tuscan adolescents. Association was confirmed between irregular breakfast habits and low frequency of fruit and vegetable consumption, and between irregular snack consumption and low frequency of fruit intake. No association was found between irregular snack consumption and low frequency of vegetable consumption.
In the analyses stratified by gender, the relation between irregular breakfast habits and fruit and vegetable consumption emerged only for the female respondents, and they appeared to be statistically consistent.
Different trends appeared when the sample was stratified by age and sex. Overall, irregular breakfast habits represented a lower risk factor for low frequency of fruit and vegetable consumption among younger girls compared with their older counterparts. An opposite pattern emerged when we considered irregular snack consumption among girls. It is important to note that the age trend changed between boys and girls and depended on whether it was fruit or vegetable intake that was considered. The association between fruit and vegetable consumption and meal frequency among teenagers is supported by other research in the field [15–19], even though the methods and instruments used to measure meal frequency and fruit and vegetable intake were different. The modifying effect of sex has not been examined in depth by any study so far.
Melnik et al.  carried out a study which showed how American children who missed meals had a lower fruit and vegetable intake, across all age groups that were considered. However, in contrast, the current study on fruit and vegetable intake and irregular eating habits has yielded several different findings for different age groups. There are many reasons for this difference in findings between the two studies. First, the analysis by Melnik et al. collected data by using a combined scale of fruit and vegetable consumption. Second, the age groups were younger than those considered in the present study. Third, their study did not stratify the analysis by gender.
There is only one similar study that has considered the modifying effects of age and gender . In that study, contrary to the results reported in the present study, it emerged that skipping breakfast, particularly among girls, represented a less serious risk of lower fruit and vegetable intake in younger school children. A possible explanation for this divergence in results could be that younger children have more opportunities to consume fruits and vegetables even if they skip meals, as parents have more control over their diet. Older children, on the other hand, are more independent and their family’s influence on their eating habits is less [42, 43].
Breakfast seems to be a determinant of vegetable intake. A strong association between irregular breakfast and low frequency of vegetable consumption was found for 15-year-old girls. This could indicate, more generally, that skipping breakfast is an indicator of unhealthy eating habits in this population. This explanation would be in consonance with other studies, which have shown that irregular breakfast habits are associated with poor nutrition [15, 18, 37]. The results of this study did not permit generalizations for irregular snack intake because the pattern consistently varied between gender, age groups and fruit and vegetable intake.
Strengths and limitations
The representativeness of the sample studied and the implementation of tested and validated methods and tools as documented in various studies  represent a strength of the present study.
As shown in literature, the validity of self-reported dietary assessment procedures among teenagers yields diverging results . FFQ is recognized as a valid tool for ranking teenagers based on their habitual food and beverage consumption [29, 44, 45].
A HBSC study from 2004/05 validated the question on breakfast frequency. It showed a reasonable accordance with food habits reported in diaries (kappa statistics 0.47) .
A further limitation of the study may be associated with the fact that only weekdays were considered for measuring frequency. We considered only weekdays because eating routines might be different during weekends. Studies have shown that generally people consume more caloric foods and generally larger portions during the weekend [47–49]. The family’s overall nutritional and meal consumption attitude could represent an underlying unmeasured confounding factor. A positive connection between family attitude towards meal consumption and children’s consumption of fruit, vegetables and breakfast has been reported in other studies [33, 34, 42]. The association between meals consumed within the family and fruit and vegetable intake may indicate an overall positive family (home) food environment where the availability of fruits and vegetables is higher and healthy meal habits are being supported [43, 49].