Background The regulation of unhealthy commodities (tobacco, alcohol and ultra-processed food and beverages) has recently garnered increased public and policy attention, with some notable public health progress in reducing associated health harms, notably tobacco. The role that distinct types of public health evidence play in supporting effective policy responses remains understudied. Our study aim was to explore views about the role of evidence in policy held by individuals working to influence policy to reduce the health harms of unhealthy commodities in the UK. Specifically, we sought to identify whether and why particular types of evidence were deemed particularly useful in achieving policy progress, how these mapped to the policy cycle, whether there were variations across tobacco, food, and alcohol policies and, if so, why.

Methods Data collection involved: 1) a cross-sectional survey among members and partners of a UK public health consortium explicitly concerned with tackling commercial determinants of health; and (2) three commodity-specific focus group discussions with relevant researchers, civil servants, and advocates (i.e. each focus group centred on a different commodity). The quantitative survey data were analysed descriptively, while qualitative survey and focus group data were analysed thematically, using an inductive approach, and mapped against the policy cycle.

Results Twenty-seven individuals completed the survey, and 15 participated in focus group discussions. Participants were working in academic, third sector and public policy organisations. There were few variations by participant sector but we did identify notable variations across the three commodities. Nonetheless, the findings suggest that different policy stages require different evidence types, with progress linked to complete ‘evidence jigsaws’: (1) Agenda-setting: evidence demonstrating harmful impacts and financial costs of unhealthy commodities; (2) Proposal formulation: evidence demonstrating likely efficacy (e.g. modelling and evidence from other international settings); (3) Policy adoption: evidence of sufficient public support (e.g. via lived experiences and public opinion polling); and (4) Implementation: evidence around compliance, effectiveness and adaptation. Evidence regarding the commercial organisations involved in manufacturing and marketing unhealthy commodities was deemed important throughout, particularly by those in tobacco control, where more such evidence is available.

Conclusion This study underscores the multifaceted role of evidence in achieving effective policy responses to unhealthy commodities, suggesting progress is only likely with complete ‘evidence jigsaws’. Evidence on unhealthy commodity industries has the potential to influence every piece of the jigsaw, which may explain why the most progress has been made in implementing policy responses to reduce tobacco harms.