Objective: To study the effects of school lessons about healthy food on adolescents' self-reported beliefs and behaviour regarding the purchase and consumption of soft drinks, water and extra foods, including sweets and snacks. The lessons were combined with the introduction of lower-calorie foods, food labelling and price reductions in school vending machines.
Design: A cluster-randomized controlled design was used to allocate schools to an experimental group (i.e. lessons and changes to school vending machines) and a control group (i.e. 'care as usual'). Questionnaires were used pre-test and post-test to assess students' self-reported purchase of extra products and their knowledge and beliefs regarding the consumption of low-calorie products.
Setting: Secondary schools in the Netherlands.
Subjects: Twelve schools participated in the experimental group (303 students) and fourteen in the control group (311 students). The students' mean age was 13.6 years, 71.5% were of native Dutch origin and mean BMI was 18.9 kg/m(2).
Results: At post-test, the experimental group knew significantly more about healthy food than the control group. Fewer students in the experimental group (43%) than in the control group (56%) reported bringing soft drinks from home. There was no significant effect on attitude, social norm, perceived behavioural control and intention regarding the consumption of low-calorie extra products.
Conclusions: The intervention had limited effects on students' knowledge and self-reported behaviour, and no effect on their beliefs regarding low-calorie beverages, sweets or snacks. We recommend a combined educational and environmental intervention of longer duration and engaging parents. More research into the effects of such interventions is needed.
Keywords: Environment; Health promotion; Obesity; Theory of planned behaviour.