Summary of findings
We evaluated the effectiveness and cost-effectiveness of HeLP, a novel school-based obesity prevention programme, in a cluster RCT involving 32 schools and > 1300 children. We found no evidence of a difference in BMI SDS at 24 months or that participating in HeLP reduced the likelihood that children would be overweight or obese compared to children not receiving the intervention. Similarly, no differences between the intervention and control groups were observed in either anthropometric measures or physical activity objectively assessed using accelerometers at 18 months post baseline. Self-reported weekly average consumption of different types of energy-dense snacks was lower in those attending intervention schools (0.4 mean difference in score), as was the number of different types of negative food markers (0.5 mean difference), small differences that were statistically significant. These differences were largely accounted for by reported differences in weekday consumption.
The cost of implementing HeLP was estimated at approximately £210 per child. Assumptions are reported regarding the proportions of children needing to move weight category for cost-effectiveness to be achieved using NICE cost-per-QALY methodology.
Comparison with other studies
Wang et al.4 is the most recent systematic review and meta-analysis of childhood obesity prevention programmes targeting both diet and physical activity. The review identified 139 intervention studies that had weight-related outcomes, of which 115 were located in the primary school. The 37 studies that were purely school-based and did not have a family component showed a low strength of evidence for reducing BMI, BMI SDS, prevalence of obesity and overweight, percentage body fat, waist circumference and skinfold thickness. However, studies that also included a family component provided moderate evidence of effectiveness, with half reporting statistically significant beneficial intervention effects. Other systematic reviews and meta-analyses also suggest that school-based obesity prevention interventions can have a modest effect on BMI SDS and it is unclear whether such effect sizes (typically < 0.1) are clinically meaningful at either a population or an individual level.7,136
We are not aware of any recent, well-conducted, school-based obesity prevention RCTs, using objective outcome measures, for this age group, that have shown a clinically relevant effect on adiposity measures at 2-year follow-up. A very recent school-based trial (Active for Life-year 5)16 involving 60 schools and > 2000 children (aged 9–10 years), which aimed to increase physical activity, reduce sedentary behaviour and increase fruit and vegetable consumption at 2-year follow-up, found no effect of the intervention on any of these primary outcomes or on weight status.
The exploratory trial of HeLP demonstrated the feasibility and acceptability of the programme, trial processes and provided evidence of ‘proof of concept’ for HeLP. Furthermore, the exploratory trial showed changes in diet and physical activity behaviours and weight status; however, these were not replicated in the main trial.28 No changes were made to the programme or trial design between the exploratory trial and the definitive RCT, with the manuals and standard operating procedures, developed in the exploratory trial, used for delivery and assessment in the main trial. In addition, HeLP was delivered as designed in all intervention schools with very high levels of engagement, as was also seen in the exploratory trial. The findings from the process evaluation allow us to be confident that the difference in results between the exploratory and the definitive trial are not due to scale-up issues of delivery. The only difference in trial design was that we had to run the main trial in two cohorts; however, there was no evidence of a differential effect of the intervention between the two cohorts on the primary outcome, indicating that this logistical requirement did not affect the overall findings, and our follow-up rates at 18 and 24 months were similar across both trials.
Understanding the lack of effectiveness
Conducting health promotion interventions within schools has the obvious potential advantage of being able to reach virtually all children. The behaviours that underlie the development of obesity and overweight in children and adolescents result from a complex interaction of individual, family and social factors. This is particularly relevant for children of primary school age, as their ability to influence their diet and activity is directly limited by decisions made by their parents/carers, as well as being affected by wider social influences. We therefore aimed to develop an intervention that would influence not only the children themselves, but also their parents and the school environment, as we felt that this would have a higher likelihood of being effective.
The design of the intervention followed the MRC’s guidance for the development and evaluation of complex interventions19 and was based on a review of research evidence and on the use of intervention mapping18 to draw on evidence regarding potentially effective methods of achieving behaviour change. Our review of existing evidence suggested that multifaceted interventions were more likely to be effective when they addressed both diet and exercise, were of significant duration and involved the family, although the strength of these conclusions was limited owing to the paucity of existing high-quality studies. We were also aware that a common reason for failure in health promotion programmes is a failure to persuade the target group to participate and to stay involved, so strategies to achieve engagement by children, parents and schools were fundamental in the design of both the intervention and the trial. In addition, for public health interventions to have an impact, they need to be deliverable without disrupting normal activities and at an affordable cost. In particular, in the context of crowded school curricula, interventions need to reduce rather than increase teachers’ workloads and, ideally, help to achieve educational targets if schools are to embrace them. We therefore worked closely with children from the target age group, parents, teachers and education advisors at all stages of the design.
We assessed the extent to which children, parents and teachers actually engaged with the programme using prespecified criteria for engagement, as well as conducting focus groups with children and interviews with parents and teachers. The results suggested very high levels of engagement across all socioeconomic groups and considerable enthusiasm for the programme. We succeeded in achieving extremely high levels of participation: only 34 out of 1371 children opted out of the trial and only 80 out of 1324 who started the study were lost to follow-up, and hence > 94% of children provided anthropometric data at 2 years and we have accelerometry data at 18 months post baseline on 84% of children (3 weekdays and 1 weekend day).
The lack of any effect of the intervention on our primary outcome measure is particularly disappointing given the high levels of engagement and that the programme was developed with substantial stakeholder involvement and reflected the current best evidence regarding techniques to change behaviour. There is a number of potential explanations: we recognise the importance of wider family and social factors in driving health behaviours, which may limit the potential effects of interventions that are delivered primarily at the level of the individual. We are also aware that although the increase in overweight among children is perceived by policy-makers as constituting a major threat to health, it is less clear whether or not parents share this view. It has been repeatedly reported that a large proportion of parents of overweight children perceive their children as being of normal weight.137 Stakeholder consultation in the development of HeLP clearly showed that focusing on weight as a health issue would not be acceptable to head teachers, teachers or parents, and thus the programme was careful to avoid discussing obesity or weight in any context. Furthermore, we believe that our very high levels of engagement support the programme’s focus on healthy lifestyle behaviours for all. However, it may be the case that the HeLP messages regarding diet and physical activity behaviours were not really seen by parents as referring to a problem that required significant and sustained behaviour change.
We chose to target children aged 9–10 years for the intervention on the basis of our early pilot work. Broadly speaking, our initial development work showed that younger children were keen to engage but did not appear to successfully absorb the messages such that they engaged their parents with them, while older children were less easy to engage. However, it is the case that, at this age, the ability of children to actually influence their own diet and activity may be limited, as, inevitably, most decisions will be made by their parents. Parental involvement in obesity prevention programmes has been frequently cited as one of the key characteristics associated with behaviour change, and throughout the programme there were activities specifically aimed at engaging parents across the socioeconomic spectrum.
Our data showed that > 50% of parents attended at least one parental engagement event, and three-quarters either attended an event or signed support for their child on the goal-setting sheet. Although it is possible to engage children (and assess their levels of engagement) in school-based programmes, the lack of direct contact with parents means that parental engagement is more difficult to achieve and assess. Many parents reported (in questionnaire responses and interview) that they had made changes at a family level and gave examples of how they were supporting their child, but this was only a subset of all of the parents involved. Given the children’s comments about the need for parental support, it is likely that the programme did not enable parents or families to make the types of sustained behaviour changes necessary to affect the weight status of their child. We consider it unlikely that school-based obesity prevention programmes will ever be of sufficient intensity to affect the family environment, and more direct approaches would be required.
We were mindful from the outset that the programme should complement educational activities (by meeting national curriculum objectives) and not be a burden to teachers. It is possible that, although the external delivery of the majority of programme activities (by sport and dance groups, actors and the HeLP co-ordinators) was welcomed by teachers and children, this delivery mode meant that the programme was probably not embedded across the school and hence could not systematically affect the school environment.
Our development and early piloting work suggested that a more intensive intervention with greater parental involvement in the programme would be less acceptable or unfeasible for schools, suggesting that those planning future obesity prevention interventions may need to consider new approaches and settings if they are seeking to affect family behaviours and the home environment.
Trial strengths and limitations
There are well-recognised potential sources of bias associated with cluster RCTs,33 including recruitment bias, performance bias and detection bias. We tried to reduce the likelihood of these biases by recruiting schools and children and collecting baseline measures before the known allocation of schools to intervention or control (to reduce differential take-up); by capturing evidence of changes in school policies around food or physical activity through school completion of a checklist at the beginning of the trial and at 18 months (see Appendix 16); and by using assessors blinded to allocation to measure the anthropometric outcomes. The primary outcome for the trial was based on measures taken when the children had transferred to secondary school, and hence secondary schools included children from both the intervention and the control groups. No child revealed their group allocation to the blinded assessor at 24-month follow-up. However, it should be noted that although the MLQ and FIQ were completed before the group allocation at baseline and at 12 and 18 months, respectively, the children were aware of their group allocation, as shown in Figure 1.
Sample size calculations, which allowed for the anticipated level of clustering as estimated from the exploratory trial and NCMP data,28,138 suggested that we needed measures from approximately 760 children at 24 months to detect a 0.25 difference in BMI SDS. We estimated that we needed 28 schools, each with approximately 35–40 children, to complete the study and so, allowing for a 20% loss to follow-up at 24 months, we sought to recruit 32 schools to allow for both school-level and child-level dropouts. No schools dropped out of the study. Few eligible children (34/1371) opted out of the study and we achieved follow-up rates of between 84% and 96% for all outcome measures, and hence there is a very low risk of attrition bias.
Reviews and recent studies of school-based obesity prevention and management trials in children have highlighted low participation, differential dropout and loss to follow-up rates.4,5,9,139 For example, completeness of anthropometric data in school-based obesity prevention programmes has ranged between 70% and 80% for follow-up of ≥ 24 months13,140,141 and the percentage of children providing a representative pattern of their physical activity levels across the entire week (at least 3 weekdays and 1 weekend day of 10 hours’ wear time) tends to be much lower (between 40% and 60%).38 In the HeLP trial, 84% of children met the minimum wear time criteria of 3 weekdays and 1 weekend day, and 79% provided data on all 7 days at 18 months. The HeLP trial, therefore, has one of the most complete follow-up rates and physical activity compliance of recent obesity prevention trials for children in this age group. We attribute this to the relational approach that we took in the trial delivery, as well as to the stakeholder involvement we had in developing the intervention and the trial design.27
We weighted our recruitment of schools to achieve a similar proportion of pupils receiving free school meals as the national average in 2012 (19%), which is higher than the average for Devon (12.7%), and the schools in the HeLP trial were larger than the average Devon primary school. In other respects, the schools that participated in the trial are representative of Devon, and the anthropometric data from the children are broadly similar to the Devon NCMP Year 6 data.142 This gives us confidence that the results are mostly applicable to a wider population. The one exception is that, although the included schools reflected the proportion of children with English as an additional language typical for Devon (2.6%), this is substantially lower than the national figure of 16.8% of pupils with English as an additional language in England.
A further strength of this trial was its robust process evaluation involving qualitative and quantitative data and its prespecified logic model and mediating variables questionnaire to understand whether or not HeLP was working in the way it was intended, with the qualitative data being analysed prior to the outcome result being known. We also attempted to assess engagement (school, child and parent); whereas school and child engagement was assessed using different methods (observation of intervention sessions and response to the programme), parent engagement was assessed as attending one of six possible parent events and/or providing a signature on the child’s goal-setting sheet. We acknowledge that this is a weak assessment of engagement and does not capture engagement with the messages of the programme. The low response rate (25%) from parents to the questionnaire about HeLP, which formed part of the process evaluation, limits the strength of these data and also suggests that the sample interviewed (who were recruited from responders to the questionnaire) is unlikely to be representative of all parents. This suggests that the qualitative data from parents cannot be considered as representative of all parents receiving the programme. However, the children recruited for the process evaluation were representative of the overall sample, and all Year 5 teachers were interviewed.
Research recommendations
The disappointing results of this study and other recent well-designed, UK-based trials suggest to us that it is unlikely that affordable, school-based interventions that are inherently time-limited can achieve clinically meaningful change in weight status/anthropometric outcomes in a single targeted age group. This view is reinforced by other research using data from the NCMP that suggested that there was no consistent school effect on childhood obesity.143 Future studies need to develop interventions that aim to specifically affect the family environment, perhaps employing a more widely co-ordinated whole-systems approach, although it is unlikely that such an approach would be feasible to deliver within a school setting.
We recognise that one reason for the lack of effectiveness of this intervention may be that, despite engaging and affecting knowledge and motivation, children of this age have limited ability to affect their own diet and levels of physical activity. This suggests that researchers should consider whether or not other age groups offer greater possibilities for affecting behaviour. It is possible that older children, who have a greater degree of autonomy, if engaged, may be more able to make changes in their behaviour. It has also been suggested that pregnant women and parents of very young children may be more amenable to adopting health messages. Examples include successful campaigns to promote smoking cessation, the avoidance of soft cheeses during pregnancy and the ‘Back to Sleep’ campaign. Programmes addressing this group (e.g. the Henry Programme: www.henry.org.uk/homepage/) have claimed impact, but rigorous evaluations are lacking and are urgently needed.
Conclusions
This cluster randomised trial provides rigorous evidence about the effects of HeLP, a novel school-based obesity prevention programme aimed at 9- to 10-year-old children, in a sample of children broadly representative of the UK population. The programme achieved high levels of engagement with children, schools and parents, but did not affect their BMI or their likelihood of being overweight or obese 2 years later compared with children attending schools in which the intervention was not delivered.