Developing a novel conceptual model of how food and drink tax policy impacts on consumption, health, environmental and economic outcomes

BACKGROUND: While food taxes are proposed to promote healthier dietary choices and mitigate diet-related diseases, addressing rising UK obesity requires navigating a highly complex web of causal mechanisms. Economic evaluations of these interventions often lack a documented understanding of this systemic complexity. To bridge this gap, this study aims to comprehensively map the system by identifying the specific components affected, the causal pathways (mechanisms), and the individual and system-level factors (context) influencing the ultimate impact of food taxes. METHODS: A diagrammatic representation of the conceptual model was developed through an iterative process. We first undertook a synthesis of reviews of food taxes and a rapid review of economic evaluations of food and drink taxes. The research team synthesised these results to describe mechanisms and outcomes for inclusion in the conceptual model. Secondly, the conceptual model was validated and revised according to feedback from 14 stakeholders across academia, policy, and third sector organisations. RESULTS: Our final conceptual model illustrates system components which were grouped into eight sub-systems including policy infrastructure, industry behaviour, consumer behaviour, household expenditure, nutrition outcomes, health outcomes, environmental outcomes, and macroeconomic outcomes. Food taxes will influence consumption through price changes impacting purchases of taxed food and other purchases resulting in changes to consumption. Industry may modify the effects by absorbing the tax burden, marketing and product development and reformulation. We identify health, macroeconomic and environmental outcomes linked to food, and explore complex feedback loops linking health and macroeconomic performance to household finances further modifying food purchasing. We identify individual and contextual factors that modify these mechanisms. CONCLUSIONS: When studying the impacts of food and drinks taxes, researchers should consider the mechanisms by which individuals and industry can modify the effects of food taxes, and the extent to which these actions can be anticipated. System-wide factors can be documented so that the modelled evidence can be interpreted considering these factors even if they are not explicitly modelled. The conceptual model v3.0 remains dynamic and can be updated as evidence and perspectives on the food tax policy system develop over time.