Background/Objectives: The Daily Health Coach (DHC) is a 12-week Instagram-based nutrition and wellbeing programme originally co-designed and tested in New Zealand to deliver evidence-based, weight-neutral content on nutrition, movement, body image, and wellbeing. This formative, mixed-methods adaptation study examined the acceptability of DHC New Zealand content for young Australian women and identified refinements to improve relevance, engagement, and safety before effectiveness evaluation. Methods: Using the CODES framework, we conducted three adaptation phases: user acceptance testing, co-design workshops, and early beta testing. Following data-quality screening, 291 young women aged 18–24 years who completed all 12 survey sections were included in Phase 1. Participants rated 84 Instagram-style posts for understanding and usefulness and provided open-ended feedback. Twelve young women participated in co-design workshops, and seven adapted artefacts were beta-tested with eight target users using cognitive walkthrough and think-aloud methods. Quantitative findings were examined descriptively, with sensitivity analyses undertaken to assess robustness to response-quality and sample-composition concerns. Results: Participant-level mean understanding was 3.99 ± 0.75/5, usefulness was 3.89 ± 0.74/5, and the combined score was 7.87 ± 1.47/10. Post-level combined means ranged from 7.66 to 8.11/10; all 84 posts met a ≥7.5 descriptive benchmark adapted from prior message-testing work, although this is an interpretive aid rather than a validated cut-off. Sensitivity analyses showed a similar overall pattern: ratings were higher in a higher-confidence response-quality sample (n = 199; 8.34 ± 1.20/10), while four posts fell marginally below 7.5 when analysis was restricted to participants not reporting Aboriginal and/or Torres Strait Islander identity (n = 101). Qualitative feedback identified six refinement areas: content features, engagement strategies, clarity, educational accuracy, relevance, and miscellaneous concerns. Co-design and beta testing generated four adaptation priorities: tone, design, engagement, and understanding. Conclusions: DHC New Zealand content was generally well understood and favourably rated but required targeted refinement for the Australian context. Findings provide formative guidance for final adaptation and subsequent effectiveness evaluation.

Background/Objectives: Social media is an important source of nutrition and wellbeing information for young women, but can amplify misinformation, appearance ideals, and difficult-to-apply health advice. The Daily Health Coach (DHC) is a 12-week Instagram-based programme, originally co-designed and tested in New Zealand, delivering evidence-based, weight-neutral content on nutrition, movement, body image, and wellbeing. This study examined the acceptability of DHC New Zealand content for young Australian women and identified refinements to improve relevance, engagement, and safety. Methods: Using the CODES framework, we conducted three adaptation phases: user acceptance testing, co-design workshops, and early beta testing. An online survey was completed by 409 young women aged 18–24 years, with 338 completing all 12 weeks of review. Participants rated 84 Instagram-style posts for understanding, usefulness, and age appropriateness and provided open-ended feedback. Twelve young women participated in co-design workshops, and seven adapted artefacts were beta-tested with eight target users using cognitive walkthrough and think-aloud methods. Results: Combined understanding and usefulness scores ranged from 7.64 to 8.10/10, with all posts meeting the prespecified acceptability threshold of ≥7.5. Understanding scores exceeded usefulness scores, indicating content was clear but not always personally relevant or actionable. Feedback identified six refinement areas: content features, engagement strategies, content clarity, educational accuracy, relevance, and miscellaneous concerns. Co-design and beta testing generated four adaptation priorities: tone, design, engagement, and understanding. Conclusions: The DHC was acceptable for young Australian women, but required targeted refinement to optimise relevance, engagement, and safety. These guidelines will inform final content adaptation and future effectiveness evaluation.

Background: Text message interventions may improve preventive health behaviours among adolescents and reduce future non-communicable disease burden, yet implementation in healthcare settings remains limited. Process evaluations are needed to understand mechanisms, context, and influences on outcomes to guide implementation. This study evaluated the acceptability, utility and engagement of the Health4Me text message intervention. Methods: Mixed methods process evaluation nested within the Health4Me randomised clinical trial (RCT; January 2023-October 2024). Inclusion criteria: (1) 12–18-years; (2) mobile phone ownership; (3) sufficient English (7th grade reading level); (4) provided e-consent (or parent/guardian consent if < 14-years); (5) living in Australia. Health4Me was a co-designed, six-month text message program to improve preventive health behaviours (nutrition or physical activity). Participants received 4-5 behaviour change text messages per week. Process evaluation at 6-months post-baseline included three data sources: text message delivery analytics, intervention feedback survey and focus groups. Quantitative data were descriptively analysed. Qualitative data were analysed using inductive content analysis (feedback survey) and Framework approach (focus groups). A weaving approach was used to integrate data sources. Findings: 390 participants provided e-consent and 365 were randomised (1:1). Of 183 intervention participants, 141 (77%) completed the feedback survey, and 37 participated in focus groups. 97% of text messages were delivered successfully. Text message content was acceptable and useful, with participants liking messages which were actionable and provided positive reinforcement. Participants were positive about intervention delivery (message frequency, duration) but reported mixed results about effects on behaviour change. Engagement was influenced by personalisation, with participants wanting more tailored content and delivery, and by trust and confidentiality, with scepticism towards some components. Interpretation: Adolescents found the intervention acceptable and useful. However, engagement varied due to the need for greater personalisation and clearer information on trust and confidentiality. The process evaluation provided suggestions to improve the intervention prior to implementation.