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PRIMEtime: an epidemiological model for informing diet and obesity policy

Background: Mathematical modelling can play a vital role in guiding public health action. In this paper, we provide an overview of the revised and updated PRIMEtime model, a tool for evaluating health and economic impacts of policies impacting on diet and obesity. We provide guidance on populating PRIMEtime with country-specific data; and illustrate its validation and implementation in evaluating a combination of interventions in the UK: a sugar-sweetened beverage (SSB) tax; a ban on television advertising of unhealthy foods; and a weight loss program. Methods: PRIMEtime uses routinely available epidemiological data to simulate the effects of changes in diet and obesity on 19 non-communicable diseases, in open- or closed-population cohorts, over time horizons from 1 year to a lifetime. From these simulations, the model can estimate impact of a policy on population health (obesity prevalence, cases of disease averted, quality-adjusted life years), health and social care costs, and economic measures (net monetary benefit, cost-effectiveness ratios). We populated PRIMEtime with UK data and validated epidemiological predictions against two published data collections. We then evaluated three current obesity intervention policies based on estimates of effectiveness from published evaluation studies. Results: There was considerable variation in the modelled impact of interventions on prevalence of obesity and subsequent changes in health and the need for health care: restrictions on TV advertising of unhealthy foods to children led to the largest reductions in obesity prevalence; but the SSB tax, which also targeted adults, had the biggest benefits in reducing obesity-related disease; and the weight loss program, while having very small impact on obesity prevalence at the population scale, had large and immediate benefits in improving health and reducing health sector spending. From a health sector perspective, the combination of interventions produced a favourable net monetary benefit of {pound}31,400 ({pound}12,200 to {pound}50,700) million. But the combined effect in reducing prevalence of overweight and obesity, was not estimated to reach more than 0.81 percentage points (95% uncertainty interval: 0.21 to 1.4) for males and 0.95 percentage points (0.24 to 1.7) for females by 2050. Conclusions: Diet and obesity interventions have the potential to improve population health and reduce health sector spending both immediately and in the long-term. Models such as PRIMEtime can be used to evaluate the economic merits of intervention strategies and determine how best to combine interventions to achieve maximum population benefit. But with almost a third of children and two-thirds of adults currently overweight or obese, we need to broaden the application of public health models to evaluating the structural and systemic changes that are needed in our society to address the underlying drivers of the obesity epidemic.