Design of a 20-month comprehensive, multicomponent school-based randomised trial to promote healthy weight development among 11-13 year olds: The HEalth In Adolescents study

Background and purpose: The lack of effective school-based interventions for preventing obesity in children has caused a call for longer duration of interventions and better reporting on design and evaluation methodology. The purpose of this paper is to present the development of the intervention, the design of the effectiveness study, and the test-retest reliability of the main outcome measures in the HEalth In Adolescents (HEIA) study. Methods/design: The HEIA intervention programme was developed based on literature reviews, a social ecological framework, and focus groups. The intervention aimed to increase total physical activity (PA) and consumption of fruit and vegetables and to decrease screen time and consumption of sugar-sweetened beverages. The intervention programme consisted of a classroom component, including dietary behaviour lessons, computer tailoring, fruit/vegetable and PA breaks, and posters, and an environmental component including active transport campaigns, equipment, suggestions for easy improvements of schoolyards, inspirational courses for teachers (all with regards to PA), and fact sheets to parents. The effect of the intervention programme is evaluated in a cluster randomised controlled trial design (intervention = 12 schools, control = 25 schools) including process evaluation. Main outcomes include anthropometry, PA, screen time, and consumption of fruit, vegetables, and sugar-sweetened beverages. A 2-week test-retest study was conducted among 114 pupils. Determinants of the behaviours were assessed. Similar data were collected from parents. Children's PA was measured objectively by accelerometers. Conclusions: The HEIA study represents a theoretically informed randomised trial comprising a comprehensive set of multilevel intervention components with a thorough evaluation using reliable outcome measures. The study will contribute to a better understanding of determinants of healthy weight development among young people and how such determinants can be modified.