Abstract
INTRODUCTION: Patients with chronic somatic diseases such as obesity often develop comorbid depressive symptoms. E-mental health interventions are an innovative and effective treatment option within a stepped care approach. Studies have shown that acceptance and adherence are higher when they are tailored to the specific needs of the target group. This study protocol describes a randomised controlled trial (RCT) of an internet-based self-help intervention, Fit4Mood, to improve mental health in the high-risk group of adults with obesity. The objective of the @ktivPLUS research project is to evaluate the effectiveness, acceptability and cost-effectiveness of the intervention in comparison to an online bibliotherapy. METHODS AND ANALYSIS: Eligible individuals will be randomly allocated to an intervention group (access to an internet-based intervention) or to an active control group (access to an online bibliotherapy). Assessments will be conducted before the start of the intervention (baseline (BL)) and 4 months after BL (follow-up (FU)). The primary outcome is the reduction in depressive symptoms (Beck Depression Inventory-II) in n=190 participants. Secondary outcomes are anxiety, quality of life, activity, self-efficacy, resilience, mental and digital health literacy, stress, sleep quality, weight loss, weight management activities and readiness to lose weight, weight self-stigma, uptake, adherence and satisfaction with the intervention, workability and cost-effectiveness at follow-up. Additionally, sociodemographics, health, comorbidities and disabilities, as well as internet-specific information, will be assessed at BL. Intention-to-treat analysis using generalised linear mixed models will be applied. ETHICS AND DISSEMINATION: Approval for this study has been granted by the ethics committee of the University of Leipzig (ID: 140/25-ek). All participants will provide informed consent prior to participation in the study. Results will be disseminated in peer-reviewed journals and presented at national and international conferences. In the case of a successful evaluation, the internet-based self-help intervention Fit4Mood will be provided as freeware, which will be easily accessible and free of charge. TRIAL REGISTRATION NUMBER: The current RCT study has been registered at the German Clinical Trials Register (Identifier: DRKS00036178, Registered 24 June 2025; https://www.drks.de/search/de/trial/DRKS00036178).