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Abstract

Background
Globally, the health of young people is in decline, with increasing rates of mental health issues, obesity and sedentary lifestyles. Existing health behaviour change interventions for this group face challenges in engagement and implementation. Effective, targeted interventions are needed to improve lifelong health outcomes for young people.

Objective
To develop, implement and evaluate a multicomponent health behaviour change intervention aimed at improving diet and increasing physical activity in young people in the United Kingdom.

Design and methods
A person-based approach drawing on systematic and literature reviews and qualitative data (interviews, group discussions and participatory ‘game jams’) was used to develop the Engaging Adolescents in Changing Behaviour intervention, which was tested using a cluster-randomised trial. A pilot trial informed modifications to recruitment, data collection and app usage processes. Schools selected two Year 8 classes (12–13 years old) to participate, with randomisation at the school level. Baseline and 12-month follow-up data on diet, physical activity and general well-being were collected from students, and demographic data were provided by schools with parental permission. An economic model was designed to estimate future effects on health outcomes of the intervention, and mixed-methods process evaluation examined participant perspectives (students, parents and teachers), LifeLab ® attendance and app download statistics.

Setting and participants
Of our planned sample of 2300, we collected baseline data from 2065 students from 45 of 49 recruited and randomised secondary schools across Hampshire and the south coast of England. Four schools dropped out before baseline data collection, and we followed up 55% of students at 1 year. The process evaluation involved 88 of these students, 23 teachers and 11 parents.

Intervention
The Engaging Adolescents in Changing Behaviour intervention had three components: experiential science education for students at LifeLab, teacher training to support students’ health behaviours and a gamified smartphone app for students to encourage better diet and physical activity.

Main outcome measures
Diet quality (standard deviation scores), total physical activity (minutes/day). Secondary outcomes included further diet and physical activity outcomes, self-efficacy for health behaviours and general well-being, assessed using both objective and self-report methods. Data were analysed using linear mixed-effects models and binary regression, accounting for clustering.

Results
Development work indicated that effective interventions should support young people’s autonomy, competence and relatedness while making healthier choices accessible and appealing. Digital platforms and social media were identified as key for engagement. Pilot findings prompted adjustments to school recruitment, data collection and app presentation for the main trial. At baseline, the intervention group had a mean diet quality score that was 0.22 standard deviation (95% confidence interval −0.05 to 0.51) higher than in the control group. At follow-up, the difference between groups was −0.02 standard deviation (95% confidence interval −0.32 to 0.27), and after adjustment for the baseline, diet quality score was −0.10 standard deviation (95% confidence interval −0.29 to 0.09). For the total physical activity outcome, the baseline difference between groups was minimal; at follow-up, the difference was 1.19 minutes/day (95% confidence interval −15.5 to 17.9) and after adjustment for baseline was 8.65 minutes/day (95% confidence interval −7.79 to 25.1). Minor differences were observed in secondary outcomes. Index of Multiple Deprivation scores of schools in intervention and control groups showed no baseline differences. Overall, 88% of eligible students attended LifeLab, and 42.5% downloaded the app. Students and teachers reported positive experiences with LifeLab and teacher training, though COVID-19 impacted in-person delivery for some schools. Students valued learning about their health but engaged minimally with the app. Parents viewed the intervention positively but often lacked communication from their children or schools about it. Teachers were eager to support health initiatives but had limited opportunities during the school day. A Markov model was produced to estimate the cost-effectiveness of LifeLab Plus, but our findings did not warrant such an analysis.

Limitations
Most students did not engage with the app due to its lack of appeal and insufficient motivation to revisit it. Only 55% of students participated in the follow-up and provided data on the diet quality score, and only 28% had complete physical activity data at baseline and follow-up. Thus, the power of the trial was reduced, making it difficult to detect differences between groups. Trials in school settings tend to include more advantaged children, as opt-in consent favours parents who complete forms. Even opt-out consent does not fully address this issue, as disadvantaged students are more likely to miss school during data collection. Demographic data collection required parental opt-in, introducing further bias.

Conclusions
The trial detected no significant impact of the intervention on diet and physical activity among secondary school students. Substantial baseline differences in diet and physical activity between intervention and control groups introduced noise, complicating conclusions about intervention effects. While schools are suitable settings for health interventions, randomised trials may not be ideal for evaluating large-scale, real-world interventions. Intervention design, particularly for smartphone applications, requires greater attention to foster sustained engagement.

Future work
Although the Engaging Adolescents in Changing Behaviour intervention did not improve diet or physical activity, it provided valuable insights. Interventions must support young people’s autonomy, competence and relatedness and offer them meaningful opportunities to support their aspirations in life. Health topics have to be important to young people to be engaging, and research has to be coproduced. Our current and future research focuses on evaluating the impact of this participatory approach on health and well-being and aims to translate findings into policy through collaborations with local authorities and Integrated Care Systems in Wessex. Exploring alternative designs for evaluating large-scale public health interventions is another important research agenda.

Publication Type:	Article
Additional Information:	Copyright © 2026 Barker et al. This work was produced by Barker et al. under the terms of a commissioning contract issued by the Secretary of State for Health and Social Care. This is an Open Access publication distributed under the terms of the Creative Commons Attribution CC BY 4.0 licence, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. See: https://creativecommons.org/licenses/by/4.0/. For attribution the title, original author(s), the publication source – NIHR Journals Library, and the DOI of the publication must be cited.
Subjects:	R Medicine > RA Public aspects of medicine > RA0421 Public health. Hygiene. Preventive Medicine
Departments:	School of Health & Medical Sciences School of Health & Medical Sciences > Department of Population Health & Policy
SWORD Depositor:	Symplectic Administrator

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