Impacts of the United Kingdom Soft Drinks Industry Levy: a systems-thinking informed systematic scoping review

BackgroundConsumption of sugar-sweetened beverages (SSBs) is associated with weight, weight gain and incidence of a number of chronic diseases. The World Health Organization recommends taxation on SSBs to reduce consumption. In 2018 the United Kingdom introduced the Soft Drinks Industry Levy (SDIL), a tiered tax on manufacturers and importers of SSBs. We aimed to review the consequences of the SDIL across all potential outcomes, informed by a systems thinking approach, to understand the range and importance of its effects. MethodsWe undertook a systematic scoping review of empirical studies of the SDIL. We used a conceptual systems map of the hypothesised pathways of effect to inform data extraction and narrative synthesis. Findings are presented in an evidence map and their consistency assessed. Results38 studies met our inclusion criteria. The SDIL was consistently associated with reformulation of soft drinks to reduce sugar content. It was also consistently associated with: reduced purchasing of sugar from eligible drinks without increasing purchasing of substitute products such as alcohol and confectionary; longer-term improvements in acute and chronic health outcomes; and reduced health and social care costs, with few negative economic impacts for industry. ConclusionsBy systematically mapping all outcomes evaluated, we have demonstrated the systemic and interconnected impacts of the SDIL. Further research should seek deeper understanding of how to evaluate such interventions as events in complex adaptive systems.