Background Healthy diet is an essential component of good health, yet many areas of the UK struggle with high burdens of diet-related diseases. Efforts to address diet-related diseases in the London Borough of Newham have had limited success so far, likely because these have not taken into account Newham’s distinct local context. Newham is ethnically diverse and within the 20% most deprived areas of England.

To approach the problem differently, we used co-design and systems approaches to develop a healthy diet intervention in Newham; these engage residents in public health action and encourage approaches that tackle the underlying causes in the food system of poor-quality diets.

Methods We ran 12 online group model building workshops with 33 Newham residents from six community neighbourhoods. Participants reflected the ethnic and religious diversity of Newham’s population. The first workshop explored residents’ views of what they believe is causing people to have unhealthy diets. Participants identified areas for action and brainstormed solutions to improve diets in the second workshop.

Results Each workshop produced a neighbourhood-specific systems map of ‘what’s causing people in Newham to have unhealthy diets’. Residents identified multiple and connected political and economic, physical environment, social-environment, and individual level causes of unhealthy diets. Suggested action areas ranged from increasing food and nutrition education and addressing the unhealthy influence of social media to alleviating poverty and improving food business practices.

Conclusion The information from workshops has been used to co-develop a context-specific food intervention with Newham food and health stakeholders. There were also key learnings from online adaptation of group model building methods.