Choice-Based Single-Session Interventions Targeting Transdiagnostic Mechanisms in Early Eating Disorder Intervention for University Students

This project is a three-arm randomised controlled trial (RCT) evaluating the feasibility, engagement, and effectiveness of delivering app-based single-session interventions (SSIs) targeting transdiagnostic mechanisms associated with eating disorder risk among university students. Participants will be university students aged 18–25 years who are currently enrolled at a university in South Australia, residing in Australia at the time of participation, and scoring ≥47 on the Revised Weight Concerns Scale (WCS), indicating elevated risk for the development of eating disorder symptoms. All study procedures will be conducted online. After providing informed consent and completing screening and baseline measures (Time 1), eligible participants will be randomly allocated (1:1:1) to one of three conditions: (1) Choice, (2) No-choice, or (3) Waitlist control. Participants in the two active conditions will receive up to three app-based SSIs delivered weekly across three weeks (Weeks 1–3) via the Cogniss platform (NouishED app). Access to each SSI is provided only after completion of the corresponding weekly measures survey; however, if a participant misses a week but completes a later weekly survey, they will receive access to the next available SSI at that time. In the Choice condition, participants will choose three SSIs (from a set of nine) and nominate the order in which they wish to receive them. In the No-choice condition, participants will be assigned SSIs based on their baseline transdiagnostic profile, such that SSIs align with participants’ highest-scoring transdiagnostic risk factors. Participants in the waitlist control condition will not receive SSIs during the three-week intervention period but will be provided access to all SSIs following completion of the post-intervention assessment (Time 4). Primary outcomes are changes in eating disorder symptoms, depressive symptoms, anxiety symptoms, and suicidality, assessed using the ED-15, PHQ-9, GAD-7, and a brief 2-item suicidality assessment. These symptom outcomes will be measured at baseline, weekly during the three-week study period (Weeks 1–3), and at post-intervention (Time 4) for all participants. Secondary outcomes include health-related quality of life (AQoL-4D) and transdiagnostic process variables (e.g., behavioural activation, rumination, self-worth, body image flexibility, distress tolerance, loneliness, self-criticism/self-reassurance, and social media motivations), assessed at baseline and post-intervention to minimise participant burden. Engagement and adherence outcomes (e.g., SSI access/opening and completion) will be captured via the intervention delivery platform, and questionnaire completion will be captured via Qualtrics. It is expected that both active intervention conditions will demonstrate improved symptom outcomes compared to the waitlist control condition. It is further expected that providing participants with choice over SSI selection and order may improve intervention engagement and adherence and may lead to stronger symptom improvements relative to guided SSI allocation. Findings will inform the feasibility and potential effectiveness of scalable, app-based transdiagnostic SSIs for eating disorder prevention and early intervention in university student populations.