A theoretically designed scale-up intervention increases adoption of an effective school nutrition program ‘SWAP IT’: outcomes of a randomised trial

Scale-up (i.e., the intentional effort to increase the reach and impact of an intervention) of effective school-based interventions is recommended to improve public health nutrition and prevent chronic disease. However, limited evidence to guide effective scale-up exists. This study aimed to assess the effectiveness of a theoretically designed multi-component scale-up intervention, designed using the Theoretical Domains Framework and Behavior Change Wheel, to increase the adoption of an evidence-based school nutrition program (SWAP IT) within primary schools in NSW Australia. We also identify any differences in the characteristics of schools adopting the program and describe the fidelity of delivering, and reach of each scale-up strategy. A parallel-group randomised controlled trial was conducted across 11 Local Health Districts (LHD) in New South Wales Australia (n = 337 schools). Primary schools which had not previously adopted the SWAP IT school nutrition program and used an existing parent communication app (Audiri) in each LHD were randomised to receive a theoretically designed multi-component scale-up intervention (n = 169 schools) or to a waitlist control, exposed to a single discrete scale up strategy (n = 168 schools). The scale-up intervention consisted of nine scale-up strategies: three ‘vertical’ strategies aiming to increase LHD Health Promotion Units capacity to scale-up and six ‘horizontal’ strategies aiming to overcome school barriers to adopting the programs. The primary outcome was school adoption of SWAP IT objectively assessed via electronic records at 6-months, assessed via logistic regression adjusting for baseline and stratification variables. Following the 6-month multi-component scale-up intervention, significantly more schools in the scale-up intervention group (n = 67/169, 40%) had adopted the SWAP IT program compared to schools in the control group (n = 0/168, 0%) (p < 0.001). Schools with a higher enrolment of Aboriginal and Torres Strait Islander students were more likely to adopt the program (p = 0.02), however no other school characteristics were associated with program adoption. Most scale-up strategies were delivered by LHD Health Promotion Units to schools with high fidelity (72–100%), however reach of the strategies varied widely (4-100%). A theoretically designed approach to scale-up, increased schools’ adoption of an evidence-based school nutrition program across a large and socio-economically and geographically diverse population. Program adoption rates were similar across socio-demographic and geographic characteristics. This approach can inform efforts of improving public health nutrition equitably through large scale adoption of school nutrition initiatives. The trial was prospectively registered on 13/02/2023 with the Australian New Zealand Clinical Trials Registry (ACTRN12623000145606). https://anzctr.org.au/Trial/Registration/TrialReview.aspx?ACTRN=12623000145606.