Healthy together Victoria and childhood obesity study: effects of a large scale, community-based cluster randomised trial of a systems thinking approach for the prevention of childhood obesity among secondary school students 2014-2016.

Background: Healthy Together Victoria (HTV) was a Victorian Government initiative that sought to reduce the prevalence of overweight and obesity through targeting chronic disease risk factors including physical activity, poor diet quality, smoking, and harmful alcohol use. The intervention involved a boosted workforce of > 170 local-level staff in 12 communities; employed to deliver system activation around health and wellbeing for individuals, families and communities. A cluster randomised trial (CRT) of a systems thinking approach to obesity prevention was embedded within HTV. We present the two-year changes in overweight and obesity and associated behaviours among secondary school students across Victoria, Australia.

Methods: Twenty-three geographically bounded areas were randomised to intervention (12 communities) or comparison (11 communities). Randomly selected secondary schools within each community were invited to participate in the trial in 2014 and 2016. Students in Grade 8 (aged approximately 13-15 years) and Grade 10 (aged approximately 15-16 years) at participating schools were recruited using an opt-out approach across July-September 2014 and 2016. Primary outcomes were body mass index (BMI) and waist circumference. Secondary outcomes were physical activity, sedentary behaviour, diet quality, health-related quality of life, and depressive symptoms. Linear mixed models were fit to estimate the intervention effect adjusting for child/school characteristics.

Results: There were 4242 intervention children and 2999 control children in the final analysis. For boys, the two-year change showed improvement in intervention versus control for waist circumference (difference in change: - 2.5 cm; 95% confidence interval [CI]: - 4.6, - 0.5) and consumption of sugar-sweetened beverages per day (< 1 serve: 8.5 percentage points; 95% CI: 0.6, 16.5). For girls, there were no statistically significant differences between conditions.

Conclusions: HTV seemed to produce favourable changes in waist circumference and sugar-sweetened beverage consumption for boys, however, no effect on BMI was observed. Although the HTV intervention was cut short, and the period between data collection points was relatively short, the changes observed in HTV contribute to the growing evidence of whole-of-community interventions targeting childhood obesity.

Trial Registration: This trial is unregistered. The intervention itself was a policy setting delivered by government and our role was the collection of data to evaluate the effect of this natural experiment. That is, this study was not a trial from the classical point of view and we were not responsible for the intervention.