Objective: This study aims to evaluate the feasibility and effectiveness of the OB-WELL program, an internet-based self-help intervention grounded in the principles of Cognitive Behavioral Therapy (CBT) and Brief Strategic Therapy (BST), designed to promote psychological well-being among individuals with obesity from the general Italian population. Methods: A three-arm randomized controlled trial with individual-level random allocation will be conducted to compare two active intervention formats - CBT and BST - with a waiting list (WL) control condition. The intervention will last six weeks and will consist of five online self-help modules followed by one individual synchronous session. Selected psychological outcomes will be assessed at baseline and immediately post-intervention (after 6 weeks). Participants in the experimental groups will also complete follow-up assessments at 3, 6, and 12 months after treatment termination.

Expected results and conclusions: Both active interventions are expected to show greater improvements immediately post-treatment compared to the waitlist (WL) condition, and these effects are anticipated to be maintained over time. It is further hypothesized that the BST condition will demonstrate greater stability of psychological outcomes at follow-up compared to CBT.

INTRODUCTION Clinical obesity is defined as a chronic, multifactorial disease characterized by excessive adipose tissue accumulation associated with measurable dysfunction in organ and tissue systems and/or clinically meaningful, age-adjusted impairments in daily functioning. Obesity exerts systemic effects across multiple physiological domains and significantly increases the risk of severe comorbidities, including type 2 diabetes, cardiovascular and cerebrovascular diseases, hypertension, dyslipidemia, several malignancies, osteoarthritis, reproductive disorders, and premature mortality.

Beyond its clinical burden, obesity represents a rapidly escalating global public health challenge. Epidemiological projections indicate a substantial increase in prevalence over the past decades, with profound implications for healthcare sustainability and resource allocation worldwide.

In parallel, robust evidence demonstrates that obesity is associated with elevated levels of psychological distress, including higher rates of depression and anxiety relative to normal-weight populations. Psychological factors-such as affective symptoms, maladaptive eating behaviors, perceived stigma, discrimination, and chronic stress-contribute not only to onset but also to the persistence and progression of obesity. Accordingly, contemporary clinical guidelines increasingly recommend the integration of structured psychological interventions within multidisciplinary obesity care pathways.

Cognitive-Behavioral Therapy (CBT) has demonstrated efficacy in improving both weight-related and psychological outcomes through techniques such as cognitive restructuring, behavioral activation, goal setting, action planning, and relaxation training. However, although short-term benefits are well established, evidence suggests that partial weight regain and attenuation of psychological gains may occur following treatment discontinuation, highlighting challenges related to long-term adherence and maintenance. Structural barriers-including high treatment costs, geographic inaccessibility, and limited continuity of care-further constrain the scalability of traditional face-to-face interventions.

These limitations underscore the need for technology-enabled, scalable, and sustainable intervention models. Digital and telemedicine-based psychological interventions have emerged as promising solutions to enhance accessibility, optimize cost-effectiveness, and support longitudinal behavioral regulation in individuals with obesity.

Systematic evaluations of digital interventions-including web-based platforms, mobile applications, telehealth systems, virtual reality (VR), and artificial intelligence (AI)-supported tools suggest that cognitive-behavioral and third-wave approaches (e.g., ACT, mindfulness-based interventions) are associated with improvements in psychological distress and maladaptive eating behaviors. Nevertheless, long-term outcome stability remains insufficiently established, with limited follow-up durations and inconsistent maintenance of treatment gains.

Alternative therapeutic frameworks may therefore warrant systematic investigation to enhance the durability of effects. Brief Strategic Therapy (BST) represents a solution-focused, systems-oriented model aimed at disrupting maladaptive and repetitive problem-maintaining strategies through targeted heuristic interventions.

Preliminary evidence from the STRATOB randomized controlled trial (RCT) suggests that BST, particularly when integrated with telecare follow-up, may enhance maintenance of psychological improvements compared to CBT, although weight outcomes were comparable across conditions. This study investigates the feasibility and effectiveness of OB-WELL, a web-based self-help intervention developed to support psychological well-being among individuals with obesity in the Italian general population. The system integrates structured therapeutic content based on either CBT or BST principles within a scalable digital delivery framework.

A three-arm RCT design is employed to compare two active internet-based intervention modules (CBT-based and BST-based) with a WL control condition. Self-reported outcome measures will be collected at baseline (T0), immediately post-intervention (6 weeks), and at 3-, 6-, and 12-month follow-ups for participants in the active conditions.

It is hypothesized that both active digital interventions will yield significantly greater improvements in psychological outcomes compared to the WL condition at post-treatment. Furthermore, treatment effects are expected to be sustained over time within the experimental groups. It is additionally hypothesized that the BST-based intervention will demonstrate greater longitudinal stability of psychological outcomes at follow-up relative to the CBT-based condition, suggesting enhanced durability of effects within a digital self-help environment.

METHODS Sample Size Calculation An a priori power analysis (F tests) conducted using G*Power software (version 3.1.9.7) indicated that 168 participants (56 per group) were required to achieve 95% power (α = .05, two-sided) to detect an interaction effect size = 0.25.

To account for potential attrition, a conservative dropout rate of 25% was assumed, consistent with previous research on internet-based self-help interventions, which has reported average dropout rates in the mid-20s across diverse populations. Accordingly, the target recruitment was increased to 224 participants, approximately 75 per group, to ensure sufficient statistical power after accounting for the expected loss to follow-up.

Procedure Participants will be recruited from the general population through a structured digital outreach strategy leveraging social media platforms (e.g., Facebook, Instagram, and Twitter) and online communities dedicated to obesity-related topics. Recruitment materials will provide standardized information regarding the study objectives, intervention characteristics, eligibility criteria, and participation procedures. They will include a secure hyperlink directing users to the study platform. As an initial screening step, participants will be asked to answer demographic questions and to complete the WSQ and the BES online. Within five days, they will attend a 30-minute semi-structured clinical interview conducted by a licensed clinical psychologist not involved in the study, further assessing eligibility and clarifying study procedures. Participants will be informed of the outcome via email within one week. In cases of exclusion, a brief explanation of the decision will be provided. Individuals presenting severe psychological distress will be encouraged to seek appropriate professional support.

Eligible participants will then be randomly allocated through an automated, computer-generated randomization procedure implemented within the Iterapi platform to one of three study arms: (1) CBT-based internet self-help intervention, (2) BST-based internet self-help intervention, or (3) WL control group. Participants assigned to the intervention arms will receive credentials granting direct access to the Iterapi platform, a secure digital platform previously used in psychological interventions. For ethical considerations, participants allocated to the WL control group will gain access to the intervention after the experimental groups have completed the 6-week treatment period.

The program comprises five structured online self-help modules, delivered in either a CBT-based or BST-based format. The modules are designed to address the following domains: (1) introduction to the intervention framework and definition of individualized objectives; (2) identification and restructuring of negative automatic thoughts; (3) recognition and regulation of emotions, with specific focus on emotional eating; (4) stress management and development of assertive communication skills; and (5) enhancement of motivation, problem-solving abilities, and self-efficacy. An additional synchronous video-meeting (Module 6) is conducted to consolidate acquired skills, support relapse prevention, and promote long-term maintenance of treatment gains.

The Iterapi platform will serve as the primary channel for communication between participants and mental health professionals, as well as for intervention delivery and collection of outcome measures.

Assessments for all participants will be administered at baseline and 6 weeks later (post-treatment). In addition, participants in the intervention groups will be followed up at 3, 6, and 12 months (follow-up). Throughout the intervention period, participants will receive weekly email notifications informing them of newly available materials on the platform. Participants who do not access the materials or fail to complete the recommended exercises will receive weekly reminders accompanied by brief motivational messages.

Although no adverse effects are anticipated, participants experiencing psychological discomfort may contact the study psychologist or consult the study coordinator at any time for clarification or further information. Participation is entirely voluntary, and enrolled individuals may withdraw from the study at any time without any consequences for current or future care.

Statistical Analysis Analyses will be conducted on an intention-to-treat (ITT) sample. Baseline comparability across the three conditions will be evaluated using chi-square tests for categorical variables and F tests for continuous variables. Continuous outcomes will be modeled using mixed-effects models with random intercepts and slopes for participants, and fixed effects for condition and repeated measures over time. Intervention effects will be indicated by significant condition × time interactions. Mixed-effects models allow the inclusion of all available data while accounting for missing values via maximum likelihood estimation. Significant overall effects will be followed by planned contrasts: first, pooling the two active interventions against the control condition, and then comparing the two active interventions directly. Statistical significance will be set at p = .05, and effect sizes will be calculated following Cohen's method. Reliable Change Indices will also be computed to assess clinically meaningful individual-level change. Statistical analyses will be conducted using SPSS software (version 31.0).

EXPECTED RESULTS Obesity represents one of the most relevant public health challenges worldwide, with a variety of adverse effects on mental and physical health. Access to psychological interventions addressing these associated psychological dimensions remains limited, highlighting the need for scalable and accessible treatment approaches.

This study aims to evaluate the efficacy of an internet-based self-help intervention designed to enhance emotional well-being, promote adaptive coping strategies, strengthen self-management skills, and improve weight-related outcomes in individuals with obesity.

We hypothesize that participants in both intervention groups will exhibit improved psychological outcomes compared with a WL control group at post-treatment. Furthermore, reductions are expected to be more pronounced among participants receiving BST relative to those receiving CBT. Direct comparison of the two intervention conditions will allow assessment of the added benefit of BST beyond the effects of the internet-based CBT intervention. Intervention usability will also be examined to guide further refinement of the program. Feasibility outcomes will be assessed using measures of program adherence, module completion rates, and participant retention throughout the intervention and follow-up periods. These indicators will provide valuable information on the acceptability, engagement, and potential sustainability of internet-based self-help interventions for individuals with obesity.

Limitations Several limitations of the study should be considered. First, participation requires sufficient internet access and basic digital literacy, potentially limiting inclusion of individuals with lower technological proficiency, particularly older adults. To address this, a preliminary usability assessment will be conducted before trial implementation to identify and mitigate platform-related barriers, with specific attention to non-digital-native users. Second, individuals with moderate to severe symptoms of mental disorders, such as clinically significant depressive symptoms, as well as those currently receiving psychological or psychopharmacological treatment, are excluded, which restricts the generalizability of the findings to the broader population experiencing loneliness. Third, the study design does not allow long-term comparison with the wait-list control, since the wait-list group is granted access to the intervention after a short delay to minimize withholding of support. Finally, as commonly observed in web-based self-help interventions, attrition rates may be higher than in face-to-face treatments. To mitigate this risk, participants will receive regular reminders and motivational messages to encourage ongoing engagement.

Inclusion Criteria:

• Adults aged 18 years or older;
• Body Mass Index (BMI) ≥ 30 kg/m²; 3. Internet access;
• Sufficient computer and internet literacy;
• Fluent knowledge of the Italian language;
• Provision of informed consent via the digital platform;
• Presence of mild or subthreshold psychological or eating-related symptoms, as identified by the Web Screening Questionnaire (WSQ);
• Presence of a score < 27 on the Binge Eating Scale (BES).

Exclusion Criteria:

• Visual, auditory, or cognitive impairments that could limit effective interaction with the digital interface;
• Diagnosis of severe psychiatric disorders according to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5);
• Insufficient digital literacy or lack of stable internet connectivity;
• Concurrent psychopharmacological treatment or ongoing psychological/psychotherapeutic intervention during the study period.

De-identified data may be available from the corresponding author upon reasonable request, in accordance with institutional and ethical regulations