Social media is a major source of nutrition and wellbeing information for young women, but it can also amplify misinformation, diet-culture messaging and appearance-based ideals. The Daily Health Coach is a 12-week Instagram-based nutrition and wellbeing programme originally co-designed with young women in New Zealand to deliver evidence-based, weight-neutral content on nutrition, movement, body image and wellbeing (1,2, 3). This study aimed to adapt the programme for young Australian women by evaluating how message framing, tone and design influenced understanding, usefulness and engagement with nutrition education content. Using the CODES framework, we conducted three adaptation phases: user acceptance testing, co-design workshops and early beta testing. A cross-sectional online survey was completed by young women aged 18–24 years living in Australia (n = 409), of whom 338 completed all 12 weeks of content review. Participants rated 84 Instagram-style posts for understanding, usefulness and age appropriateness using 5-point Likert scales and provided open-ended feedback. Combined understanding and usefulness scores were calculated out of 10, with ≥7.5 prespecified as acceptable. Quantitative data were analysed descriptively, with one-way ANOVA used to examine differences across content themes and education levels. Open-ended responses were thematically analysed. Co-design workshops were conducted with young women (n = 12), and seven adapted content artefacts were subsequently beta-tested with target users (n = 8) using cognitive walkthrough and think-aloud methods. Across 84 posts, combined understanding and usefulness scores ranged from 7.64 to 8.10 out of 10, with all posts meeting the acceptability threshold. Understanding scores were consistently higher than usefulness scores, suggesting that content was generally clear but not always personally relevant or actionable. Theme-level scores were tightly clustered, with no significant differences across content themes (F(6, 77) = 0.67, p = 0.67, η² = 0.05). A significant difference was observed across education levels (F(5, 66) = 54.20, p < 0.001, η² = 0.80). Qualitative feedback identified six areas for refinement: content features, engagement strategies, clarity, educational accuracy, relevance and miscellaneous concerns. Co-design and beta-testing findings consolidated these into four practical adaptation priorities: tone, design, engagement and understanding. Young women preferred concise, visually consistent, locally relevant content using supportive, non-judgemental language, practical examples and clear links to trustworthy evidence. The adapted Daily Health Coach was acceptable for young Australian women, but required targeted refinement to optimise relevance, engagement and safety. These findings offer practical guidance for community-based digital nutrition education interventions delivered through social media.