Krølner et al. BMC Public Health 2012, 12:191 http://www.biomedcentral.com/1471-2458/12/191 Background Many adolescents in western countries, including Den- mark, do not meet the World Health Organisation’s (WHO) recommendations of a daily intake of at least 400 grams of fruit and vegetables (FV) [1,2]. Especially the vegetable intake lags behind [1,2]. Moreover, FV intake among children decreases as they enter the teen years [3]. The international Health Behaviour in School-Aged Chil- dren (HBSC) surveys among 11-, 13-and 15-year-olds show a significant decline in proportions of children eating FV daily by age in almost all countries and most consis- tently among boys [4,5]. The reason for the decline from age 11 to 15 is unknown. Well-established modifiable determinants among children and adolescents are home availability, parental intake and children’s FV taste prefer- ences [3] but these factors may not be sufficient to explain age differences in FV intake. Qualitative studies suggest that peers, short term outcome expectancies, situational norms and different aspects of availability such as variety, convenience and attractiveness of FV and access to unhealthy food may be important for teenagers’ FV intake [6]. Furthermore, the transition to secondary school may involve new habits and influences for adolescents as they sometimes change school environments, and may exercise more autonomy over their own food choice. They have increased opportunities for eating unhealthily as they are often allowed to leave school during breaks, spend more time and meals together with their friends and have their own money to spend which limits their parents’ influence as role models and caretaker for their dietary behaviour. Teenagers’ food choice may function as a statement of independence and detachment from parents as well as a symbolic marker of social identity and belongingness to certain peer groups [6-9]. FV intake in the early teens may be crucial as longitudinal studies show that the frequency of FV intake at the age of 13-14 years is a good indicator of frequency of consumption in young adulthood [10,11]. Few interventions have targeted secondary school-aged children (13-18 years of age) and with mixed results [12,13]. Reviews of intervention studies among children and adolescents have concluded that theory-based, multi- component school-based approaches of a long duration and intensity combining educational and environmental strategies in school with parent involvement are most effective in increasing FV consumption [12,14,15]. Availability of FV The importance of availability of FV for adolescents’ FV intake has been confirmed in literature reviews of both qualitative studies, observational studies and intervention studies [3,6,12,14,15]. Intervention studies in Norway, Belgium, and Canada have shown that free provision of fruit and/or vegetables in schools can increase adoles- cents’ fruit and/or vegetable intake [16-21]. Studies from Page 2 of 25 Norway suggest that free FV programmes are more effec- tive than subscription programmes in increasing fruit consumption [18]. Subscription programmes may increase social inequality in FV intake as subscribers include mainly high income families whereas free provi- sion increases intake among adolescents from families of low socioeconomic position (SEP) as well [18]. Most interventions have reported larger effects for fruit intake than vegetable intake [21-24] and it remains a challenge to develop effective methods to increase vegetable consumption. Many intervention studies have only succeeded in increasing FV intake in school, not the total daily intake which may be explained by minimal parental involvement and by the fact that FV provided in schools replace some of the FV eaten at other times of the day [19,22]. Imple- mentation of home components is challenging as few par- ents tend to participate [25,26]. Home availability and accessibility, parental intake, and SEP are all consistently associated with adolescents’ FV consumption [3,27]. It is therefore important to develop strategies which increase parental involvement and support to adolescents’ FV intake [28]. The Pro Children multi-component interven- tion programme which included a family component (par- ental newsletters, family home assignments) together with FV provision (free or subscription) and a classroom curri- culum had a significantly positive effect on total daily fruit-, vegetable-and FV intake among 10-11-year-olds in Norway, the Netherlands and Spain at 8-month follow-up [21]. Multi-component interventions have been suggested to be more effective than single component strategies due to synergistic effects between educational and environmental strategies [29]. Other studies suggest that a single strategy which only increases access to FV is equally or even more effective in increasing adolescents’ FV intake [17,30]. Inter- vention components such as curricular activities are not always implemented as intended. Low fidelity and small doses delivered challenge the validity of assessments of the effectiveness of multi-component interventions [31-33]. Therefore, thorough process evaluation, including detailed monitoring of the implementation is important [32,33]. Computerised individualised tailoring of nutrition edu- cation seems to be an effective method of nutrition interventions among adults [34,35]. The evidence for the effectiveness among adolescents is unclear [36-38]. The method has the potential to be an effective intervention strategy as it is a popular intervention activity in this age group [39]. A review from 2010 concluded that dynamically tailored interventions (ipsative feedback) had increased efficacy over time as compared with tai- lored interventions based on one assessment only [40]. However, this approach has not been widely tested among adolescents.