Co-Designing a Web-Based Nutrition Intervention for Individuals with Severe Mental Illness Using the Behaviour Change Wheel

Individuals with severe mental illness face significant health disparities and reduced life expectancy, with nutrition recognised as an important modifiable factor in health outcomes. Digital tools may support healthier eating behaviours; however, few digital nutrition interventions have been specifically designed for this population or developed with accessibility and inclusion as central design priorities. This study aimed to co-design a web-based nutrition intervention for individuals with severe mental illness using the Behaviour Change Wheel. Intervention development followed a three-stage, eight-step process. A previous behavioural analysis identified three key targets for change: improving nutrition knowledge, enhancing meal preparation skills, and increasing digital literacy. These targets informed the initial intervention content and delivery strategies. Twenty participants, including individuals with lived experience of severe mental illness and mental health professionals, participated in co-design sessions that informed intervention refinement. Participants highlighted the importance of simple navigation, plain language, short videos, visual supports, staff involvement, reminders, and incentives to support engagement. Preliminary usability testing indicated high levels of usability, with feedback informing refinements to navigation, content delivery, and accessibility features. To enhance accessibility and inclusivity, the intervention was developed in line with the Principles of Universal Design, supporting equitable and non-stigmatising access, flexible content delivery, simple and intuitive navigation, perceptible information, and low user effort. This intervention aligns with UN SDG 3 (Good Health and Wellbeing) and SDG 10 (Reduced Inequalities). Findings support the value of integrating co-design, behavioural science and Universal Design in digital health intervention development for this population.