This study has received approval from the institutional review board at Yeshiva University (43318060.0). To our knowledge, the intervention does not pose any significant risks to participants, although some participants may become distressed while engaging in the treatment because we are addressing sensitive content (eg, difficult emotions, ED urges, and eating). All questionnaires have been validated in numerous prior studies. However, some questionnaires involve questions on ED symptoms and diagnoses and other psychological difficulties, which may elicit distress in some participants. All participants will provide signed consent after being informed of study procedures and objectives, possible risks, and the right to withdraw from participation at any time.

Participants will receive up to US $180 for completing study assessments. This will include US $20 for the baseline visit, US $30 for the midtreatment assessments, US $40 for the end-of-study assessments, US $60 for the 2-month follow-up assessments, and US $30 for completing all lessons (for participants in the Mindful Courage+coached self-monitoring condition only). We decided to provide incentivization for app adherence because we are in an early stage of treatment development, and we wanted to ensure that participants were fully exposed to the intervention to provide acceptability ratings.

All data will be collected and stored via Qualtrics. Qualtrics is HIPAA secured and uses industry-standard encryption, supports access controls, and has audit logs. Deidentified data will be stored on secure cloud servers and will be retained for a minimum of 5 years. Full access to data will be given only to the principal investigator and approved research staff. Zoom sessions will not be recorded.

The digital intervention CBT-based Mindful Courage was developed through an iterative process considering patient feedback and consists of 16 sequential core lessons, which are completed across 18 weeks (Multimedia Appendix 1). Each lesson takes approximately 40 to 50 minutes to complete and includes several key features to promote engagement [36-39], including multiple animated videos, audio-guided meditation practices, interactive activities and questions to help participants understand the intervention content in a personally relevant manner, and supportive feedback. After completing each core lesson, participants are instructed to complete 2 audio-guided mindfulness meditation sessions that last 10 to 15 minutes before the next core lesson. The program includes 2 narrators, both clinical psychologists, who appear as avatars in the animated videos to guide participants through the lessons. The program also features several fictional patients, voiced by professional actors hired through Fiverr, who share their experiences through client testimonials and discussions with the 2 psychologists.

The CBT content is derived from enhanced CBT for EDs [9] and a condensed CBT for EDs [40]. The mindfulness content is adapted from a digital MBI for substance use disorder (NCT05852015) developed by Roos et al [35], a prior digital MBI for anorexia nervosa developed by Sala et al [22,23], and several standardized MBI and acceptance and commitment therapy protocols [41-45], particularly mindfulness-based relapse prevention [41].

The intervention also combines CBT and mindfulness techniques. For example, (1) we combine self-monitoring and mindful awareness to increase awareness of eating patterns that may trigger binge eating, (2) we encourage mindful awareness of the consequences of irregular eating, (3) we instruct participants to use mindfulness strategies to notice in their daily life how using CBT strategies (such as reducing dietary restraint and eating satiating meals) affects hunger or fullness and binge eating urges, (4) we combine reduction of valuation of weight and shape with values work, (5) we encourage awareness of ED behaviors and of the relationships between ED behaviors and ED symptoms, and (6) we encourage awareness of factors that may contribute to lapses and relapses.

The animated videos were built with Powtoon, an online animation creation program; the digital lessons were created in Qualtrics; and videos were hosted in Vimeo. Audio content was recorded and edited with Audacity. See Figure 1 for examples of CBT-based Mindful Courage visuals.

Participants in both conditions will be asked to self-monitor their food intake using Recovery Record [46], a frequently used digital intervention among individuals with BED [47]. Participants will not be asked to engage with any other features of Recovery Record. We chose to ask participants from both conditions to track their food intake as regular eating is the foundation of ED recovery [48].

Participants in both conditions will receive phone coaching by psychology students during the 18-week treatment period but not during the follow-up period. Phone coaching for both conditions will include weekly coaching calls (10-15 minutes, except for week 1, which will be 30 minutes) and extra technical support as needed via phone and SMS text message. In addition, for participants in CBT-based Mindful Courage, there will be 1 to 2 weekly SMS text message reminders to use CBT-based Mindful Courage and additional phone or SMS text message contact (up to 1 weekly call and 2 weekly SMS text messages) for participants not engaging in CBT-based Mindful Courage. The aim of the phone coaching is to provide general motivational and technical support rather than provide any specific therapeutic intervention.

Participants in this condition will not have access to CBT-based Mindful Courage but will be asked to self-monitor their food intake in Recovery Record and will receive phone coaching.

Participants in this condition will have access to CBT-based Mindful Courage for 18 weeks. Participants will also be encouraged to engage with Recovery Record self-monitoring of food intake and will also receive phone coaching.

We will establish BED diagnosis using the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, 5th edition [49]. Other inclusion criteria will be assessed with 1-item questions in an interview-based assessment.

Benchmarks for feasibility are based on previous digital interventions for EDs [31,62-64], and include (1) feasibility of recruitment (40 participants randomized); (2) feasibility of randomization (75% of eligible screens randomized); (3) intervention completion (34/40, 85% of randomized individuals completing at least 1 module; average completion rates of 60% for the 16 lessons) assessed objectively via Qualtrics; (4) completion rates for midtreatment, end-of-treatment, and 2-month follow-up visits (32/40, 80% of participants completing the midtreatment visit, 30/40, 75% of participants completing the end-of-treatment visit, and 26/40, 65% of participants completing the follow-up visit).

Acceptability will include dimensions of usability from the System Usability Scale [65]. We also created additional single-item questions, drawing upon the Technology Acceptance Model [66], evaluating overall satisfaction, engagement, visual appeal of content, understandability of program content, desire to continue the program, perceived skill acquisition, perceived confidence in implementing skills, and perceived helpfulness of CBT-based Mindful Courage. Participants in the CBT-based Mindful Courage+coached self-monitoring condition will rate their responses to each item from 1 (strongly disagree) to 5 (strongly agree). Given that this is the first pilot feasibility trial of CBT-based Mindful Courage, and our primary intention is to evaluate whether this intervention has preliminary promise for acceptability, benchmarks for these items will be conservatively set to an average score of >3.5 (agree).

BED-related outcomes, examined on an exploratory basis to estimate effect sizes for a full-scale RCT, will include (1) frequency of binge eating episodes in the last 28 days, which will be assessed with the Eating Disorder Examination Questionnaire (EDE-Q) [50]; and (2) ED symptoms, assessed with the global EDE-Q score. Additional outcomes will include (3) changes in clinical impairment measured via the Clinical Impairment Assessment [51] and (4) depressive symptoms measured via the 9-item Patient Health Questionnaire-9 [52]. All these measures have demonstrated adequate psychometric properties [51,67-72].

We will measure mechanisms of change due to the intervention on an exploratory basis. This will include (1) emotion dysregulation, measured via the Difficulties in Emotion Regulation Scale-Short Form [53]; (2) dietary overrestriction, measured via the restraint subscale of the EDE-Q [50]; and (3) trait mindfulness, measured via the Cognitive and Affective Mindfulness Scale-Revised [54]. All these measures have demonstrated adequate psychometric properties [54,67,73].

We will collect additional measures to be used in exploratory analyses. At baseline, we will collect data on duration of illness, past treatment experiences, past meditation experiences, and eating self-monitoring app use. We will also collect data on adverse events, positive and negative affect measured via the Positive and Negative Affect Schedule [55], savoring measured via the Savoring Beliefs Inventory [56], food craving measured via the Food Cravings Questionnaire-Trait-reduced [57], anxiety symptoms measured via the Generalized Anxiety Disorder-7 item assessment [58], body satisfaction measured via the Body Shape Questionnaire [59], binge eating symptoms measured via the Binge Eating Scale [60], and BMI derived from self-reported height and weight.

See Figure 2 for a graphic of the study timeline. Online advertisements will include a link for an online prescreening (via HIPAA-secured Qualtrics surveys). Interested participants can then use this link to be assessed for preliminary eligibility; this will include questions on age, ability to engage in the research study, and the Eating Disorder Diagnostic Scale [61]. If individuals meet preliminary eligibility based on the online prescreener, they will be invited to a complete a HIPAA-secured Zoom-based screening interview with a trained psychology student. The Zoom-based screening interview will include informed consent, administration of the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, 5th edition [49] to confirm BED diagnosis, and a semistructured interview-based assessment to evaluate inclusion and exclusion criteria (refer to the Measures section).

If participants are eligible and willing to continue, they will be randomly assigned to either coached self-monitoring or CBT-based Mindful Courage+coached self-monitoring by the psychology student who completed the screening interview. Following our prior work [35], randomization will be achieved using a web-based computerized urn randomization program that ensures balance across treatment groups based on sex, age, binge eating severity, and race or ethnicity. Allocation concealment will be ensured because the program reveals assignments only after participant enrollment. After randomization, participants will proceed to the baseline study session (also conducted over Zoom by the psychology student; Multimedia Appendix 2) and will be instructed on how to track their food intake in Recovery Record. They will also receive the orientation for phone coaching. Participants randomized to the CBT-based Mindful Courage+coached self-monitoring condition will be instructed on how to access CBT-based Mindful Courage (either on their computers or via Android or iPhone) and will complete session 1 of the intervention as part of the visit. After completing session 1, participants will be informed that they will have 18 weeks of access to the app to complete 16 lessons and the 2 accompanying mindfulness practices, with weekly support from a student coach.

After the baseline visit, participants will complete 3 follow-up assessments: (1) midtreatment assessment (weeks 8-9), (2) end-of-treatment assessment (to be administered within 2 weeks of completing the final lesson or reaching the end of the study period; weeks 16-20), and (3) a 2-month follow-up (2 months after the end of treatment; weeks 24-28). The exact assessment timeline may vary for each participant according to scheduling availability and whether the 16 lessons are completed before the end of the study period.

We will use descriptive statistics to examine feasibility and acceptability of CBT-based Mindful Courage. Both groups will be included in analyses of recruitment feasibility, randomization, and assessment completion, whereas only participants in the CBT-based Mindful Courage group will be included for evaluating acceptability and feasibility of intervention completion. Specifically, we will compute average scores and frequencies for all feasibility and acceptability benchmarks.

On an exploratory basis, we will evaluate changes in outcomes and mechanisms from baseline to each subsequent assessment point using linear mixed models, separately for participants in each of the conditions (n=20 in each condition). Mixed models enable the inclusion of all participants regardless of missing data (ie, an intent-to-treat analysis). We will also calculate Cohen d effect sizes for changes within condition.