Investigating the effect of a cognitive-behavioral therapy intervention aimed at reducing weight self-stigma on adherence to weight loss diet and anthropometric indices in adult women with obesity: study protocol for a randomized controlled trial

Abstract

Background

Obesity is a complex and chronic condition with serious health risks, including higher chances of diabetes, heart disease, and certain types of cancer. Weight self-stigma, prevalent among individuals with obesity, exacerbates psychological distress and negatively impacts adherence to weight loss diets. Cognitive-behavioral therapy (CBT), a psychological intervention targeting maladaptive beliefs and behaviors, has shown promise in addressing weight self-stigma. However, the specific impact of CBT, delivered in a group therapy format, on adherence to prescribed weight-loss diets has not yet been adequately investigated, particularly among women with obesity, who are disproportionately affected by both the condition and weight self-stigma.

Methods

This research is a two-arm, parallel-group randomized controlled trial aimed at assessing the effectiveness of a group-based CBT intervention in mitigating weight self-stigma and enhancing adherence to a weight-loss diet and anthropometric outcomes in adult women with obesity. Participants (n = 120) who meet the inclusion criteria will be randomly allocated to one of two groups: (1) CBT in addition to a personalized weight-loss diet, or (2) only the personalized weight-loss diet. The CBT intervention will consist of 1.5-h weekly online group therapy sessions over 12 weeks. Outcome assessments, including adherence to the weight loss diet and changes in anthropometric measures (fat-free mass (FFM), fat mass (FM), and body mass index), will be performed at baseline and 4, 8, and 12 weeks. Adherence will be assessed based on changes in FM and FFM to avoid reliance on self-reported data. Additional assessments will include scores from validated psychological and health-related questionnaires, including the Weight Self-Stigma Questionnaire, the Weight Bias Internalization Scale, and the General Health Questionnaire.

Discussion

This study aims to clarify its role in improving dietary adherence and weight management outcomes by addressing weight self-stigma through a CBT intervention. If successful, the findings could inform healthcare strategies and contribute to developing comprehensive interventions for obesity management. The study is expected to provide evidence for integrating psychological support into weight loss programs, particularly for populations most affected by stigma. We suggest that this trial has the potential to refine therapeutic approaches for weight management in women with obesity.

Trial registration

IRCT20140907019082N12 Registered on November 25, 2023.

Introduction

Background and rationale {6a}

Obesity, a relapsing condition marked by excessive or abnormal fat accumulation either subcutaneously or centrally, is recognized as a chronic and complex disease with serious health consequences [1]. As of 2022, over 1 billion people worldwide are affected by obesity. Obesity rates in adults have more than doubled since 1990 [2]. Similar to global trends, the prevalence of obesity has been steadily rising in Middle Eastern countries, with approximately one-fifth of adults suffering from obesity [3]. According to a 2023 study by Abiri et al., the estimated prevalence of obesity is 13.44% (95% CI: 11.76–15.22) in Iran [4]. Adipocyte hyperplasia, hypertrophy, and the formation of visceral fat in non-adipose tissues in obesity contribute to cardiovascular and liver diseases. It also induces hyperglycemia, insulin resistance, and activates associated inflammatory signaling pathways, leading to further conditions related to obesity, like cancer and type 2 diabetes [5]. Obesity is categorized using the body mass index (BMI), a formula that calculates a person's weight in kilograms divided by their height in meters squared (kg/m²). A BMI of 18.5 to 24.9 kg/m² is considered normal weight; 25 to 29.9 kg/m² shows overweight; and a BMI of 30 kg/m² or more is characterized as obesity [6]. Obesity is classified into different classes: Class 1 (BMI 30 to 34.9), Class 2 (BMI 35 to 39.9), and Class 3 (BMI over 40) [7], each is associated with adverse health consequences of varying intensity [8–10]. Epidemiological evidence shows that obesity is more prevalent among women [11–13], who are also more likely to experience weight self-stigma than men [14].

Weight self-stigma is a psychological consequence of obesity, characterized by perceived weight-based discrimination, feelings of shame, and unfavorable self-assessments [15]. Weight stigma manifests in two ways: self-stigma and public stigma. Public stigma, or external stigma, involves facing discrimination in social situations, whereas self-stigma, or internalized stigma, happens when individuals adopt societal stereotypes about obesity [16, 17]. Weight self-stigma is related to adverse effects on physical and mental health, such as negative body image, reduced physical activity, binge eating, anxiety, depression, and an increased risk of cardiovascular disease [18].

Aladel et al. noted a negative association between quality of life domains, food quality/quantity, and weight self-stigma. They also emphasize the need for developing social policies to prevent or mitigate its impact [15]. Another study found that weight self-stigma negatively affected the ability of adults with type 2 diabetes to maintain optimal dietary self-care and engage in physical activity [19]. In a survey of 3,821 adults, Prunty et al. discovered that weight self-stigma was correlated with a higher likelihood of hyperglycemia, non-arthritic chronic pain, and hypertension. They noted that reducing weight stigma may help control several physical health conditions [20]. In a study involving 508 adults experiencing obesity or overweight, Schram et al. found that weight self-stigma significantly and negatively impacted both engagement in and the outcomes of an online weight loss intervention [21]. Lillis et al. conducted a study on the association between weight self-stigma and results of a behavioral weight loss program, proposing that efforts to lessen weight self-stigma could improve weight loss outcomes [22]. D'Adamo et al. conducted a systematic scoping review indicating that psychological interventions, such as cognitive-behavioral therapy (CBT), are acceptable and feasible, potentially enhancing health outcomes for those with weight self-stigma [23].

CBT is a psychotherapeutic intervention designed to help individuals in identifying and restructuring faulty beliefs and thought patterns, thereby promoting emotional well-being and mental health [24]. Evidence indicates that cognitive-behavioral approaches can be effective in reducing stigma across various populations, including individuals with different mental and physical illnesses [25–27]. Group-based CBT, in particular, may provide additional benefits through positive peer modeling, social support, and reinforcement [28]. Learning cognitive-behavioral techniques in a group setting may explain the effectiveness of this intervention for stigmatized individuals [18]. To our knowledge, the evidence on group-based CBT for weight self-stigma is limited to three studies by Pearl et al., including two randomized controlled trials [18, 29] and one pilot study [30]. The pilot study, which included eight men and women, demonstrated that CBT reduced weight stigma and improved treatment outcomes [30]. Another 26-week RCT, published in 2020 and involving 72 participants, demonstrated that group-based CBT led to short-term decreases in specific aspects of weight self-stigma [18]. A more recent study, published in 2023 and involving 105 participants, mostly women and with an average BMI of 38, found that CBT was related to improved eating self-efficacy and certain aspects of quality of life [29]. Although these studies have made valuable contributions by examining the application of CBT in addressing weight self-stigma and its impact on weight management, they leave a significant gap in understanding the effect of CBT interventions on adherence to prescribed diets. The importance of this issue is underscored by a systematic review reporting that weight self-stigma is related to poorer dietary adherence [31]. In contrast, adherence to a prescribed diet plays a crucial role in the success of weight loss interventions [32].

Building on the existing evidence, the present study aims to investigate whether online group-based CBT intervention reduces weight self-stigma, enhances adherence to prescribed diets, and consequently, improves weight loss outcomes, focusing specifically on women with obesity. This focus is justified by epidemiological evidence demonstrating that women are more vulnerable to both obesity and weight self-stigma. Addressing this gap has the potential to provide healthcare professionals with a more comprehensive understanding of CBT's effectiveness for women with obesity. These findings could inform the development of more impactful, evidence-based strategies for sustainable weight management.

Objectives {7}

Primary Objective: To evaluate the efficacy of a CBT intervention, delivered alongside a prescribed weight-loss diet, in improving adherence to the diet and reducing weight self-stigma among adult women with obesity.

Secondary Objectives: To evaluate the impact of the CBT intervention, delivered alongside a prescribed weight-loss diet, on achieving favorable changes in anthropometric indices, general mental health status, and to assess the relation between weight self-stigma and adherence to a prescribed weight-loss diet among adult women with obesity.

Primary Hypothesis: It is hypothesized that participants receiving CBT in addition to a prescribed diet will demonstrate greater reductions in weight self-stigma, which will in turn lead to significantly improved dietary adherence, general mental health status, and more favorable changes in anthropometric measures compared to those receiving only the prescribed diet.

Trial design {8}

The current research is structured as an RCT with a two-arm, parallel-group design, as presented in Fig. 1, to assess the effectiveness of a CBT intervention designed to reduce weight self-stigma on adherence to a weight loss diet and improvements in anthropometric indices in adult women with obesity. After a baseline evaluation, participants will be randomly allocated to one of two groups: the usual care group (control group), which will receive the structured weight loss diet alone, or the experimental group, which will undergo the CBT intervention alongside a structured weight loss diet. The allocation proportion will be 1:1. Participants will undergo assessments at baseline, after 1 month, 2 months, and post-intervention (3 months) to improve the interpretation of adherence patterns throughout the study.

Fig. 1.

Flow chart of the RCT study

Methods: Participants, interventions, and outcomes

Study setting {9}

The research will be conducted in Tehran, Iran.. Individuals meeting the study's criteria will be selected from nutrition and diet therapy clinic attendees.

Eligibility criteria {10}

Inclusion criteria

To be included, participants must meet all of the following criteria:

• Female gender

• BMI between 30 and 40 kg/m.² at baseline (chosen to ensure a more homogeneous sample and enhance clinical interpretability)

• Age between 18 and 50 years

• Diagnosis of weight self-stigma confirmed by a clinical psychologist (based on weight self-stigma questionnaire (WSSQ) score ≥ 36)

• Signing informed consent and willingness to participate in the study

• The necessary facilities and ability to participate in online group-based therapy sessions

• Ability to attend monthly face-to-face visits and comply with scheduled in-person assessments

Exclusion criteria

Participants will be excluded if they:

• Decline to sign the informed consent form or choose to withdraw at any time

• Are diagnosed with major psychiatric disorders (e.g., schizophrenia, bipolar disorder, major depressive disorder, bulimia nervosa, schizoaffective disorder, generalized anxiety disorder) or are currently using antipsychotics (e.g., risperidone, olanzapine), mood stabilizers (e.g., valproate, lithium), or certain antidepressants (e.g., mirtazapine, amitriptyline) medications

• Have medical conditions that may affect body weight or metabolism (e.g., Cushing’s syndrome, hyperthyroidism, hypothyroidism, polycystic ovary syndrome, uncontrolled diabetes, or heart failure)

• Have received specialized psychological treatment for weight self-stigma within the past three months

• Are taking medications known to significantly affect body weight or appetite (e.g., prednisone, insulin, megestrol acetate, appetite suppressants, antipsychotics, or certain antidepressants)

• Are breastfeeding, pregnant, or planning pregnancy during the study period

• Are unable to attend monthly in-person follow-up sessions (e.g., due to relocation or other logistical barriers)

Who will take informed consent? {26a}

Following the clinical team's first evaluation, a trained research coordinator with expertise in informed consent procedures will provide qualified participants with verbal details and an informational pamphlet regarding the study. Subsequently, participants will be informed about the research goals, highlighting their voluntary participation before the research coordinator obtains written consent.

Additional consent provisions for collection and use of participant data and biological specimens {26b}

The consent form will ask participants if they agree to allow their data to be used after leaving the study trial. It will also inquire about sharing relevant data with researchers from participating universities or regulatory authorities if necessary. Notably, this trial will not include collecting biological samples for storage.

Interventions

Explanation for the choice of comparators {6b}

The current study aims to determine the impact of a CBT approach to reduce weight self-stigma on adherence to a low-calorie diet in adult women with obesity. The control group will follow only the low-calorie diet, representing the standard clinical practice intervention. Dietary interventions are a fundamental component of obesity treatment, and among these, calorie restriction is a widely recommended strategy. Although various forms of calorie restriction exist, continuous energy restriction, which was used in this study, is one of the most established and commonly cited methods [33]. Its widespread use allows for a reliable assessment of the added value of CBT beyond dietary intervention alone.

Intervention description {11a}

The intervention group will engage in an online CBT program aimed at reducing weight self-stigma through weekly 1.5-h online group sessions. Table 1 outlines the full session schedule; key topics of the sessions are briefly summarized below: Introduction to weight stigma and psychoeducation: defining weight bias/stigma concepts and sharing personal experiences (e.g., examples of encountered bias). Challenging weight-related myths and stereotypes: examining common misconceptions about weight with evidence (e.g., biological/environmental factors in weight) and beginning to dispute self-defeating beliefs. Cognitive restructuring of negative thoughts: identifying and reappraising weight-related cognitive distortions using the CBT “triangle” and thought records, with practice reframing self-criticism to support healthy behaviors. Coping with external stigma: learning strategies for dealing with interpersonal bias (e.g., asserting boundaries, DEAR MAN skills) and evaluating pros/cons of response styles in stigmatizing scenarios. Self-efficacy and empowerment: building self-confidence (e.g., positive self-talk, advocacy, self-compassion) to counter internalized stigma and sustain health goals.

Table 1.

Summary of the 12 weekly CBT sessions for weight self-stigma reduction

Session	Title	Summary of Content	Discussion Topic	Homework (for Next Session)
1	Psychoeducation and Program Introduction	Introduce the CBT program structure, set group guidelines, and familiarize members with one another and the facilitators. Define key terms (e.g., weight bias, stigma)	Share personal experiences of weight bias and stigma	Note instances of weight bias in media, daily life, or personal beliefs
2	Challenging Weight Stereotypes	Identify and challenge common myths and stereotypes about weight, and provide psychoeducation on the biological and environmental determinants of weight	Evaluate evidence for and against prevalent weight-related misconceptions	Track and record any negative automatic thoughts about weight or body image
3	Cognitive Distortions and Thought Records	Introduce common cognitive distortions; teach the use of thought-record sheets to track negative automatic thoughts related to weight	Analyze examples of negative automatic thoughts and ways to restructure them	Practice completing thought records; bring examples of identified negative thoughts
4	CBT Triangle and Cognitive Restructuring	Explain the CBT “triangle” model (thoughts, feelings, behaviors); practice cognitive restructuring to modify negative weight-related thoughts	Explore how thoughts, feelings, and behaviors interact; practice reframing negative thoughts	Use the CBT triangle to journal any negative thoughts, emotions, and behaviors, and attempt to reframe one negative thought
5	Negative Thoughts as Barriers to Healthy Behavior	Examine how self-critical thoughts can hinder healthy eating and physical activity, and discuss the impact of internalized stigma on lifestyle choices	Discuss examples of self-critical thoughts that discourage nutritious eating or exercise	Identify one negative self-thought related to diet or exercise, challenge it, and replace it with a positive or neutral thought
6	Responding to Weight Bias: Pros and Cons	Review different strategies for responding to experiences of weight bias; discuss goals of effective interpersonal responses (assertiveness, etc.)	Evaluate the pros and cons of assertive, aggressive, and avoidant reactions to stigma	Write a script for an assertive response to a weight-biased comment; mentally rehearse this scenario
7	Responding to Weight Bias: DEAR Model	Teach the DBT-based DEAR skill (Describe, Express, Assert, Reinforce) for assertive communication in response to stigma	Create and role-play response scripts using the DEAR model for a weight-stigma scenario	Practice using the DEAR technique in daily life when encountering stigma; note the outcomes
8	Reducing Self-Criticism and Coping Strategies	Address internalized self-criticism; introduce coping strategies (e.g., self-advocacy, positive affirmations) to counteract self-stigma	Examine patterns of self-blame; discuss methods to reduce self-criticism and increase self-compassion	Practice a chosen coping strategy (such as a self-affirmation exercise or calling a supportive organization) and record any insights
9	Building Self-Efficacy and Confidence	Focus on enhancing self-efficacy and confidence in pursuing health-related goals; set personal behavioral objectives	Identify past successes and personal strengths; discuss strategies for maintaining motivation	Set a specific, short-term goal related to eating or exercise; outline concrete steps and practice positive self-talk to help you achieve it
10	Acceptance and Self-Compassion	Discuss the balance between body/self-acceptance and health goals; teach self-compassion techniques for coping with lapses or setbacks	Explore feelings about body acceptance vs. desire for change; address guilt/shame related to weight and setbacks	Practice a brief self-compassion exercise (e.g., loving-kindness meditation) and journal any thoughts or feelings during the practice
11	Positive Self-Talk for Relapse Prevention	Teach using positive, compassionate self-dialogue when facing perceived dietary “slips” or setbacks	Contrast the effects of negative self-criticism versus positive encouragement on emotions and behavior	If a diet lapse occurs, write down the negative self-talk and reframe those statements into positive or growth-oriented ones
12	Program Review and Future Planning	Review all topics and skills learned; reflect on personal progress; develop an individualized plan for coping with weight bias moving forward	Discuss changes in beliefs or attitudes over the course; set long-term self-care and weight-management goals	No new assignment (participants continue to apply the skills independently)

The 60 participants in the CBT group will be randomly divided into six subgroups of 10 participants each. While online delivery may pose certain limitations in group dynamics, previous research suggests that online CBT interventions can still be significantly effective across various psychological outcomes [34, 35]. The decision to conduct online sessions was made to reduce common barriers to access, such as travel time and financial costs, and to allow participants to access therapy without the fear of stigma associated with psychiatric disorders or being seen attending psychiatric service [34]. Participants without experience with online sessions will receive training from a trained technician to ensure they can access and use the online platform effectively. Both groups will obtain the standard care, including a personalized weight-loss diet designed to reduce daily caloric intake by 30% of Total Daily Energy Expenditure (TDEE, with a minimum of 1,200 kcal/day), calculated using the McArdle formula. The macronutrient composition of diet plans will consist of 50–53% carbohydrates, 15–18% protein, and 30–32% fat. The intervention will span three months, with an in-person visit scheduled at the start of each month conducted. After collecting the data, the calculations will be performed again, and each individual's diet plan will be adjusted based on the new calculations.

A Content Evaluation Panel consisting of 10 specialized experts, including three psychologists, four nutrition specialists, one senior health education specialist, and two general practitioners, was formed to evaluate the quantification of content validity. The panel will be provided with all the content prepared for use in group-based therapy sessions. The panel members will be tasked with thoroughly reviewing the material and assessing its content validity. Subsequently, the Content Validity Ratio (CVR) and the Content Validity Index (CVI) will be evaluated.

Two indices, the CVI and the CVR, were employed to estimate content validity quantitatively. For this purpose, the group-based therapy session content titles were presented as an evaluation checklist in a questionnaire, accompanied by printed content given to the expert panel.

Panel members will first evaluate each item independently to calculate CVR. using a three-point scale: "essential," "useful but not essential," and "not necessary." All responses will then be aggregated to compute CVR using the subsequent formula:

$$\text{CVR}=(\text{nE}-\text{N}/2)/(\text{N}/2)$$

In this formula, nE denotes the count of experts who deemed the item essential, while N signifies the overall number of panel members. Lawshe's table will help confirm the content validity [36]. Based on Lawshe's table, a panel of 10 experts required a minimum CVR value of 0.62 to validate each item's content. Since the CVR for all items exceeded this threshold, the content validity of all items was confirmed.

To assess the CVI, panel members were requested to evaluate each item separately based on three criteria: clarity, relevance, and simplicity, using a 4-point Likert scale (e.g., 1: irrelevant, 2: somewhat relevant, 3: relevant, and 4: highly relevant). To calculate the CVI, we divided the number of responses rated 3 or 4, the highest scores, by the total number of experts' scores. An item's content validity was confirmed when its CVI score exceeded 0.79. Since all items scored above 0.79, the content validity for all items was confirmed.

Criteria for discontinuing or modifying allocated interventions {11b}

Participants can withdraw from the study for any reason and at any time, without facing consequences. Additionally, the research team reserves the right to remove any participant who is uncooperative or does not meet follow-up requirements. Failure to meet follow-up requirements is missing at least three group-based therapy sessions or three monthly in-person appointments.

Strategies to improve adherence to interventions {11c}

The research team will contact participants weekly to answer their probable questions or concerns related to their diet or group-based therapy sessions and to enhance compliance. Participants will have daily access to a dietitian or psychologist via text messaging and can schedule phone consultations on a designated day each week. Additionally, participants will receive text message reminders the day before their scheduled online group-based therapy sessions and in-person appointments. Moreover, since the psychological intervention is delivered online, participants can attend sessions from their preferred locations without traveling, which enhances convenience and flexibility. This online format is expected to facilitate participation and may help to reduce the likelihood of dropout.

Relevant concomitant care permitted or prohibited during the trial {11d}

Concurrent care will be permitted without restrictions, allowing all participants to continue their usual care routines without interruption. Participants' medications and supplements will be documented before the start of the intervention, and their continued use will be allowed throughout the study. Participants should inform the researchers of any changes in their medication throughout the intervention to ensure these adjustments are recorded and considered in the analysis.

Provisions for post-trial care {30}

No particular post-trial care is scheduled since the study is a low-risk intervention. Upon completion of the study, each participant will receive a health report status, including weight and body composition changes. This information will help determine if continuing the weight-loss diet is appropriate. If the CBT intervention proves effective, participants in the control group will be offered the opportunity to undergo the same intervention after the study concludes as an ethical and supportive follow-up option.

Outcomes {12}

Primary Outcome:

The main outcome will be the change in adherence to the diet among the groups and the differences between the groups, which will be calculated using Pedro et al. 's method [37]. This approach, which will evaluate adherence based on body composition changes, will offer greater reliability than other methods by eliminating reliance on recall and self-reported data. The TDEE, which represents the total number of calories an individual burns daily, will be assessed to assess adherence to the weight loss diet using the McArdle formula at the beginning and end of each month of the intervention. The average of these two measurements will be recorded as the individual's TDEE for that month. Subsequently, the difference between TDEE and the caloric intake prescribed by the weight loss diet will be calculated and used as the expected daily calorie loss. Additionally, changes in fat-free mass (FFM), which refers to the total body mass excluding fat, and fat mass (FM), which is the total mass of all the fat in the body, will be measured for each individual at the beginning and end of each month. These changes will be converted into energy equivalents using coefficients of 1.1 kcal/g for FFM loss, 9.3 kcal/g for FM loss, and 1.8 kcal/g for FFM gain. The total calorie loss will then be calculated using the following formula:

$$\text{total kilocalories lost}=[\text{FM lost}(\text{g})\times 9.3\text{kcal}/\text{g}]+[\mathrm{\Delta }\text{FFM}(\text{kg})1.1\text{or}1.8\text{kcal}/\text{g}]$$

Following this, the actual daily calorie loss will be determined by dividing the total calorie loss during each month of the intervention by the number of intervention days:

$$\mathrm{Actual}\mathrm{daily}\mathrm{kilocalorie}\mathrm{loss}=\mathrm{total}\mathrm{kilocalorie}\mathrm{loss}/\mathrm{intervention}\mathrm{days}$$

Finally, adherence to the weight loss diet will be calculated by comparing the actual daily calorie loss to the expected daily calorie loss using the following formula:

$$\mathrm{Percentage}\mathrm{adherence}\mathrm{to}\mathrm{weight}\mathrm{loss}\mathrm{diet}=[\mathrm{Actual}\mathrm{daily}\mathrm{kilocalorie}\mathrm{loss}]/[\mathrm{expected}\mathrm{daily}\mathrm{calorie}\mathrm{loss}]*100$$

Changes in weight self-stigma will be measured using two validated instruments administered at baseline and post-intervention: scores of the weight bias internalization scale (WBIS), which assesses the degree to which individuals internalize negative weight-related stereotypes, and the WSSQ, designed to measure internalized weight stigma and its psychological impact [38]. The Persian versions of WBIS and WSSQ have been previously validated, demonstrating acceptable reliability and validity in Iranian populations. Internal consistency for the subscales of WSSQ showed Cronbach’s alpha coefficients of 0.75 and 0.78, and 0.86 for the overall questionnaire [39]. Psychometric evaluation of the WBIS also demonstrated good internal consistency (α = 0.84) and satisfactory construct validity based on confirmatory factor analysis [40].

Secondary Outcomes:

• Anthropometric indicators, including BMI, FM, and FFM, will be measured using a body composition analyzer (InBody 270 Body Composition Analyzer) at baseline and the end of each month of the intervention.

• The general health questionnaire (GHQ-28), a screening tool used to identify psychological distress and general mental health status [41], will be assessed at both the baseline and the conclusion of the study. The Persian version of the GHQ-28 has been validated, showing good sensitivity (84.7%) and specificity (93.8%), with strong concurrent validity [42].

• The relationship between WBIS/WSSQ scores changes and percentage adherence to the weight-loss diet will be examined statistically to explore potential mediating effects.

• Participants' demographic and socio-economic information will be collected and analyzed as potential confounding variables, allowing for a more accurate interpretation of variability in adherence outcomes across participants.

Participant timeline {13}

Table 2 presents our RCT study's interventions, enrolment, and assessment schedule.

Table 2.

RCT study’s interventions, enrolment, and assessment schedule

The RCT study schedule of enrolment, intervention, and assessment procedures (according to SPIRIT guidelines)

Sample size {14}

We conducted a statistical power analysis informed by earlier research [18] to calculate the sample size, using an alpha of 0.05 and a power of 0.80, along with an effect size of 0.56 via G*Power 3.1.9.7. Consequently, the estimated sample size is 106, with 53 participants in each group. Ultimately, assuming a 15% dropout rate, the total sample size was determined to be 120 individuals.

Recruitment {15}

Participants will be recruited from a nutrition and diet therapy clinic's outpatients in Tehran, Iran. The study's purpose and procedures will be explained to in-person clients during their visit, and they will also receive a written summary (flyers, brochures, etc.) for reference. Additionally, former clinic clients meeting the initial eligibility criteria will be reached out to, and details of the study will be communicated to them. If they express interest, an appointment for an in-person consultation will be scheduled. All interested candidates will be referred to a coordinator to confirm their eligibility in accordance with the study's inclusion criteria.

Assignment of interventions: allocation

Sequence generation {16a}

After the baseline examination, eligible individuals will be randomly assigned to either the usual care group or the intervention group in a 1:1 ratio. An independent statistician not involved in intervention delivery, assessment, or participant recruitment will generate the randomization list using computer-generated permuted block randomization with a fixed block size of 4 via the online platform https://www.sealedenvelope.com. This method ensures proper allocation balance, impartiality, and minimizes selection bias.

Concealment mechanism {16b}

The assignment sequence will be concealed using a secure, password-protected, web-based system within the sealed envelope platform, accessible only to the independent statistician. Allocation information will be released only after the clinical research coordinator confirms participant enrollment. This approach prevents prior knowledge of group assignments and maintains allocation concealment from the investigators and participants until the assignment is made.

Implementation {16c}

The independent statistician will generate the randomization sequence. The clinical research coordinator will screen and enroll eligible participants according to the study’s inclusion and exclusion criteria. Once enrollment is complete, the independent statistician will assign participants to one of the two groups based on the pre-generated randomization list. Investigators delivering the intervention will be aware of group assignment due to the study's nature. However, outcome assessors and data analysts will remain blinded, consistent with the protocol’s blinding procedure.

Assignment of interventions: Blinding

Who will be blinded {17a}

Neither the research team nor the patients in either group can be blinded to the patient allocations due to the nature of the intervention. However, the team responsible for assessing outcomes and those conducting Statistical analysis and data evaluation will remain blinded to the group assignments.

Procedure for unblinding if needed {17b}

The study employs an open-label design, in which only the outcome assessors are blinded, indicating that unblinding will not occur.

Data collection and management

Plans for assessment and collection of outcomes {18a}

A questionnaire will gather sociodemographic and baseline information from all participants, including names, ages, contact information, number of children, marital status, education level, income, occupation, medical history, current medications, and supplements. The research team will assess all participants' anthropometric measurements and body composition. Height will be measured using a Seca standing stadiometer, and weight, FM, and FFM will be measured using the InBody 270 Body Composition Analyzer. BMI will be calculated by dividing weight (kg) by the square of height (m²). We will assess physical activity levels through the International Physical Activity Questionnaire (IPAQ) [43], which has been psychometrically validated in Iran. It demonstrates acceptable validity and reliability, with strong internal consistency and test–retest reliability [44]. This tool will help calculate TDEE. The score of weight self-stigma will be assessed using the WSSQ and the WBIS. A score of ≥ 36 on WSSQ, confirmed by a clinical psychologist as indicating significant weight self-stigma and suitability for a weight stigma–focused intervention, based on evidence linking this cutoff to greater psychological symptoms and poorer weight management [21]. To maintain data quality, trained data collectors, supervised by the principal investigator, will uniformly and reproducibly gather all data.

Plans to promote participant retention and complete follow-up {18b}

Participants will receive details about the purpose of the study and its relevance. The importance of fully participating in the treatment and follow-up evaluation will be emphasized, highlighting the study's integrity and the potential personal benefits of therapy. The research team will additionally implement strategies to improve participant retention. These strategies include periodic and consistent communications aimed at reminding individuals of scheduled in-person visits and participation in online group-based therapy sessions through phone calls and text messages. Additionally, all expenses, such as dietitian consultations, diet planning, body composition assessments, and group-based therapy sessions, will be fully covered for all participants throughout the study.

Data management {19}

To enhance data quality and precision, all information shall be entered twice and meticulously verified by two independent researchers. The data collected will be stored at Tabriz University of Medical Sciences in Iran, with access restricted exclusively to statisticians and data administrators. Every patient will be assigned a distinct and confidential participant ID, accessible only to the research team. All personal data will be encoded. We will ensure that patients' private information is separated from their medical records database.

Confidentiality {27}

Each participant will be assigned a unique study identification code for data storage. In the online group-based sessions, participants will also use a unique code as their username to enter the sessions, ensuring that their personal information and identity remain confidential during online interactions. All participants will be informed about the confidentiality procedures of the study, including data storage, coding, and the protection of personal information, during the consent and enrollment process. Throughout the study, the research team will access the key that connects these codes to the participants. The study data will be securely stored on encrypted, password-protected servers in the principal investigator’s office. Any physical documents, such as consent forms or paper questionnaires, will be stored in locked filing cabinets in the same office. Access to electronic and physical data will be strictly limited to authorized study personnel directly involved in the research. No identifiable personal information will be shared outside the research team. To ensure compliance with potential journal or regulatory requests, anonymized electronic data will be retained indefinitely in encrypted form. However, any physical records containing personally identifiable information will be securely destroyed one year after the publication of the study results. Once the study concludes, the principal investigator will record and securely store this key following research guidelines. No personal information from participants will appear in any publications. If participants choose to withdraw their consent from the survey, any data collected until that point will still be utilized and analyzed unless they specifically rescind permission to analyze their data. If a participant stops engaging with the study intervention but does not withdraw from participation entirely, further data needed for the study can still be gathered and used.

Plans for collection, laboratory evaluation, and storage of biological specimens for genetic or molecular analysis in this trial/future use {33}

This does not apply to the present study because this trial does not include the collection of biological specimens for storage.

Statistical methods

Statistical methods for primary and secondary outcomes {20a}

Analysis of data will utilize both the intention-to-treat (ITT) and per-protocol approaches. All participants will be encouraged to complete outcome assessments regardless of adherence to the intervention, allowing for an intention-to-treat analysis without missing data. The Kolmogorov–Smirnov test will be applied to assess the normality of data distribution. Levene’s test will be used to evaluate the homogeneity of variances. Quantitative data following a normal distribution will be reported as means with their standard deviations, while qualitative data will be shown as frequencies with their percentages. The Chi-square (χ2) test will be used to compare the baseline qualitative characteristics between study groups, with Fisher's exact test applied as needed. The Independent Sample t-test will compare quantitative variables between the intervention and control groups before the intervention. A one-way mixed repeated measures analysis of variance (ANOVA) will be employed to evaluate how effective the intervention is. The effect size will be determined using ηp2, with a p-value below 0.05 deemed statistically significant. The changes between the two groups through intervention will be assessed using pairwise comparisons from the repeated measures ANOVA. In the event of missing outcome data, linear mixed-effects modeling will be employed as a more robust alternative to accommodate incomplete data under the assumption of missing at random (MAR). Sensitivity analyses will also be performed to evaluate the robustness of findings across different analytical approaches. Additionally, a linear regression analysis will be performed using both observed (baseline and post-intervention) scores and change scores (i.e., post-intervention minus baseline values) to examine the relationship between variables. The statistical package for social science version 26 was utilized for statistical data analysis.

Interim analyses {21b}

No interim analyses will be conducted regarding the trial's primary objective.

Methods for additional analyses (e.g., subgroup analyses) {20b}

No subgroup analysis will be conducted.

Methods in analysis to handle protocol non-adherence and any statistical methods to handle missing data {20c}

Both per-protocol and ITT analyses will be employed. All participants will be included in the final ITT analysis. Participants who do not fully adhere to the study protocol will still be encouraged to complete outcome assessments at the end of each month, allowing their data to be incorporated into the ITT analysis. In cases where no final evaluation is possible, such as due to migration or loss to follow-up, missing data will be addressed using the Maximum Likelihood Estimation method. For the per-protocol analysis, missing data will not be imputed; only complete, available data will be analyzed. The extent of missing data and its potential impact on study findings will be reported and discussed in the final results section.

Plans to give access to the full protocol, participant-level data, and statistical code {31c}

The corresponding author can provide the non-identifiable datasets used and/or analyzed during the current study, along with the complete protocol, upon reasonable request and in accordance with Tabriz University of Medical Sciences' research collaboration and data transfer guidelines.

Oversight and monitoring

Composition of the coordinating centre and trial steering committee {5d}

The principal investigator is the researcher in charge of designing and executing the trial. Along with research physicians, dieticians, and psychologists, they oversee participant treatment, recruitment, and follow-up. The responsible staff for recruitment activities selects eligible subjects and ensures that the hiring process adheres to established criteria and protocols. A steering committee will be established to oversee the whole study. The study team will also keep in constant contact to track the research progress.

Composition of the data monitoring committee, its role, and reporting structure {21a}

A data monitoring committee will not be formed because of the trial's short duration and the low risks linked to the treatment regimens.

Adverse event reporting and harms {22}

This study will not involve any harmful events or adverse effects because of the intervention's nature.

Frequency and plans for auditing trial conduct {23}

A report will be submitted to the auditor every six months.

Plans for communicating important protocol amendments to relevant parties (e.g., trial participants, ethical committees) {25}

All protocol changes require approval from the Ethics Committees at Tabriz University of Medical Sciences in Iran. Participants will be informed of any changes if these amendments affect them. If needed, further consent will be obtained and recorded. Additionally, online trial registries will be revised accordingly.

Dissemination plans {31a}

All findings from the RCT will be presented at international and national scientific conferences in nutrition, psychology, and related disciplines. In addition, a comprehensive report of the study will be submitted for publication in peer-reviewed journals. The results will also be shared with study participants, healthcare providers, and relevant healthcare professionals. Furthermore, the study outcomes may be available through public databases or institutional repositories, ensuring broad accessibility to the wider scientific and medical community. No publication restrictions have been imposed by the study sponsor or funding body.

While assessing content validity, we actively encouraged collaboration and feedback from prospective participants to ensure patients' public involvement in the research. We connected with individuals who offered valuable insights, enabling us to create a CBT intervention that is both efficient and tailored to their needs. They played a crucial role in shaping the intervention’s design and content, ensuring it was relevant and accurate.

Discussion

This research was designed to evaluate the effect of a CBT intervention on weight self-stigma and to address two key questions: How much does weight self-stigma affect adherence to a weight loss diet, and can reducing it improve adherence?. Considering the higher prevalence of both obesity and weight self-stigma among the female population, we specifically targeted women suffering from obesity to closely evaluate the issue and better control for potential confounding factors. This approach emphasizes adherence as a crucial behavioral outcome and a key mediator of intervention effectiveness.

In therapeutic interventions, adherence is crucial and is described by the World Health Organization as “the extent to which a person's behavior, taking medication, following a diet, and/or executing lifestyle changes, corresponds with agreed recommendations from a health care provider.”. Also, non-adherence is recognized as a problem of 'striking magnitude' [45]. This is particularly relevant for weight loss interventions, where adherence to prescribed strategies is critical for long-term and short-term success. Without adherence to these recommendations, patients are unlikely to achieve successful weight loss [46]. Earlier research has indicated a negative correlation between psychological distress and adherence to medical recommendations [47–49], highlighting the significance of psychotherapeutic approaches in the treatment process. Despite these insights, no study has investigated the effect of a psychological intervention, such as CBT, on changes in adherence to a weight loss diet intervention following potential improvements in weight self-stigma. Thus, the current study aims to bridge this gap by demonstrating whether, and to what extent, a CBT-based intervention targeting weight self-stigma can influence the success of a prescribed weight loss diet.

Despite the novelty of this study, several limitations should be considered and will be carefully accounted for when interpreting future results. The considerable sample size and the need for ongoing weekly psychological counseling led to the use of online group-based therapy sessions, which may have influenced participant engagement or interaction, and this will be factored into the interpretation of outcome efficacy. Due to financial constraints, adherence was assessed using body composition indices, whereas doubly labeled water probably could have provided more accurate measurements. This methodological choice will be acknowledged as a potential source of measurement bias in assessing adherence outcomes. Although this adherence method is grounded in validated physiological principles, it has not been specifically validated in this population. It may affect individual-level accuracy and should therefore be interpreted cautiously. Furthermore, the study population was limited to women with a BMI range of 30–40, which may restrict the generalizability of the findings to individuals with different BMI categories or to males. Accordingly, the applicability of findings will be cautiously interpreted, recognizing this population-specific limitation. Future research may address these limitations by incorporating hybrid or in-person formats that enhance therapeutic engagement, securing additional funding to employ gold-standard methods like doubly labeled water for dietary adherence, and expanding participant inclusion criteria to other BMI ranges and male populations to improve generalizability.

In conclusion, this trial study could introduce a new approach to obesity treatment in women, offering insights for healthcare providers. Examining the impact of CBT on weight self-stigma and adherence can refine treatment strategies and improve weight management outcomes. If proven effective, this intervention may provide a structured, scalable, and non-pharmacological option for enhancing adherence and addressing psychological barriers in weight loss programs, particularly in women who experience high levels of weight-related stigma.

Trial status

This study is ongoing and will continue until September 2025.

Abbreviations

BMI

Body Mass Index

CBT

Cognitive-Behavioral Therapy

CVI

Content Validity Index

CVR

Content Validity Ratio

FFM

Fat-Free Mass

FM

Fat Mass

GHQ-28

General Health Questionnaire (28-item version)

IPAQ

International Physical Activity Questionnaire

RCT

Randomized Controlled Trial

TDEE

Total Daily Energy Expenditure

WBIS

Weight Bias Internalization Scale

WSSQ

Weight Self-Stigma Questionnaire

Authors’ contributions {31b}

MSF participated in the study design, management, subject recruitment, and manuscript writing. AHLJ assisted in manuscript writing and statistical analysis. MAF was responsible for the study's conception and supervised its execution.

Funding {4}

A grant from Tabriz University of Medical Sciences in Iran funded this research. The funders had no role in study recruitment, data collection, analysis, design, or interpretation. Their role was limited to providing financial support.

Data availability {29}

The datasets created or analyzed in this study can be obtained from the corresponding author upon a reasonable request.

Declarations

Ethics approval and consent to participate {24}

The study protocol has been reviewed and approved by the Ethics Committee of Tabriz University of Medical Sciences (Approval ID: IRCT20140907019082N12). Before enrollment in the study, we will obtain written informed consent from each individual. All study procedures will follow the ethical principles outlined in the Declaration of Helsinki and relevant institutional guidelines.

Consent for publication {32}

Publication consent is not relevant.

Competing interests {28}

The authors state that there are no conflicting interests.