Program ideas
The name of the research project 'Dutch Obesity Intervention in Teenagers' led to the acronym 'DOiT', and became the central theme of the intervention program. 'DOiT' refers to the growth of behavioural self-determination, distinctive for the age of our target group. Close collaboration with professional designers and representatives of the target group representatives led to a 'fresh', 'cool', and 'not too childish', but 'more mature' logo (see
Additional file 2) and appearance of the intervention materials.
Personal interviews with teachers and parents revealed that it was of utmost importance that words related to 'weight loss' or 'dieting' should be avoided in the intervention program. Hence, the main message of the intervention program consisted of 'maintaining energy balance', and extra attention was paid to distinct messages with regard to unhealthy dieting practices, such as anorexia nervosa or bulimia nervosa.
Intervention program and materials
Guided by tables
1 and 2 we first selected components from existing intervention programs that could fit into a school-based intervention program with a duration of one school-year (i.e. eight months, from October – May), tailored to the specific objectives of the DOiT-project. We adopted several ideas from a the 'Krachtvoer' program [
57], an intervention promoting healthy eating among Dutch adolescents of the same age and socio-economic background as our target group. Suitable components were selected and integrated in cooperation with biology and physical education teachers, since they were supposed to implement the larger part of the program. If existing tools were not available, were not well enough tailored to the objective(s), were not accepted by the teachers, or their use was too costly, we either customized parts of already existing tools or developed new tools.
The DOiT-intervention program consisted of two components: an individual classroom-based intervention and an environmental intervention.
The individual classroom-based intervention consisted of an educational program, covering 11 lessons for the biology and physical education classes. Two 'schoolbooks' were developed, accompanied by specific worksheets for each lesson.
The first six lessons of the classroom intervention, named BALANCEiT (see
Additional file 3), aimed at raising awareness and information processing with regard to energy balance-related behaviours. The adolescents monitored their own behaviour during three days, using a pocket-sized diary named CHECKiT (see
Additional file 4), reported it back in the classroom, and received feedback from the teacher. Based on this monitoring process, the intervention program guided the adolescents in their choice which of the four risk behaviours they were going to change initially and helped to formulate implementation intentions [
58]. Implementation intentions are not only formulated intentions of behaviours or behavioural changes to be accomplished, but they include a specification of circumstances wherein the behaviour is accomplished. The formulation of implementation intentions has shown to be effective in changing energy balance-related behaviours [
59‐
61].
The second five lessons of the classroom intervention, named CHOOSEiT (see
Additional file 5), aimed at facilitation of the choice to improve one of the identified risk behaviours. Assisted by the teachers and worksheets, adolescents identified their own risk behaviour(s), set personal goals, formulated implementation intentions, identified possible barriers/difficult situations, improved their self-efficacy, and evaluated change processes. Offering the adolescents the possibility of individual choice on how to maintain their energy balance, and not forcing them into one prescribed behavioural change, seems to be a potentially effective ingredient of our intervention [
62]. To provide adolescents with individualized feedback and guide the adolescents through the change processes, a computer-tailored program was developed, which was based on existing materials [
63], and accessible via the internet [
64] or CD-rom. Computer-tailored education has shown to be more effective regarding dietary changes, especially with regard to the reduction of dietary fat, than general information [
65].
To fit the DOiT-intervention optimally into the regular curriculum, the main objectives of the regular biology and physical education curricula, formulated by the Dutch Ministry of Education, Culture and Science, were taken into account.
The environmental part of the intervention consisted of a school-specific advice on the assortment of the school canteen, taking into account individual school characteristics and possibilities (for example distance to the nearest supermarket, policy with regard to permission to leave the school ground during breaks, or the relationship between the school canteen and the school board [in the Netherlands school canteens are run by either the school itself or outsourced to an independent entrepreneur]). Proposed change options were: offering smaller portion sizes (cans instead of bottles, normal size instead of king size); offering more 'healthy' products in the (products containing less fat, less sugar); or restricting access to vending machines (i.e. only after lunch break). In addition, we delivered posters for the school canteens, with 'traffic-light' suggestions for healthier choices. Foodstuffs were thus labelled as red ('Better do not'), yellow ('Only sometimes'), or green ('DOiT').
Furthermore, we encouraged the school board to offer additional physical activity options. We offered schools funding for two weekly hours of additional physical activity, under the following conditions: (1) The lessons should be supervised by a physical education teacher; (2) the lessons should fit within the school schedule (no break between the last official school lesson and the additional lesson physical activity); (3) a minimum number of twelve lessons should be taught between November 2003 and April 2004; (4) easy accessible activities, i.e. no specific knowledge or physical conditions necessary; (5) adolescents should be physically active during a major part of the lesson; (6) activities during the lessons should encourage adolescents to increase their leisure time physical activity as well.
Adoption and implementation plan
In this step of the IM process, a plan for the implementation of the intervention was developed. Performance objectives were formulated with regard to expected behavioural changes of implementers and adopters of the intervention program. To gain insight into facilitating factors and possible barriers regarding the implementation, teachers and school staff were interviewed at schools, willing and unwilling to adopt the program.
In the planning of the program, a time schedule for deliverance of the intervention program was formulated, taking into consideration extracurricular activities. Based on this schedule it was decided that the intervention should start October 2003 and end in May 2004, to ensure time wise a comparable implementation in all schools. All teachers received a manual describing the structure of each lesson and goals for the distinctive parts of the lessons.
The principle investigator indicated to be available for teachers via mail or telephone any time for possible questions on the intervention.
Evaluation plan
In this step of IM an evaluation plan and the corresponding evaluation measures were identified and developed, covering as much as possible the evaluation steps, as defined in the CONSORT statement [
66,
67], a checklist that intents to improve quality of reports of randomised controlled trials, by clarifying experimental processes.
We evaluated the intervention with regard to effects on body composition (primary outcome measure), behaviour, behavioural determinants, and aerobic fitness (secondary outcome measures). We also conducted a process evaluation to assess the reach, adoption, and implementation of the program, as well as conditions for program maintenance, such as appreciation of the project by students and school staff.
The effectiveness of the intervention program was evaluated using a cluster randomised controlled trial design, with measurements at baseline, after eight, twelve, and twenty months. The Medical Ethical Committee of the VU University Medical Center (Amsterdam, The Netherlands) approved the study protocol.