Metacognitive interpersonal therapy-eating disorders versus cognitive behavioral therapy for eating disorders for non-underweight adults with eating disorders: study protocol for a pilot pre-registered randomized controlled trial

Eating disorders (ED) are serious disorders characterized by an alteration of eating habits and excessive concern about weight and body shapes (Fairburn, 2002), accompanied by significant impairment inequality of life, high mortality rates and serious organic consequences (Jenkins et al., 2011; Treasure et al., 2015; 2020). Although evidence-based psychological therapies for nonunderweight ED presentations such as cognitive behavioral therapy for eating disorders (CBT-ED) are widely available, there is substantial scope for improvements, particularly in terms of efficacy and adherence. One option is to develop interventions to address elements of pathology not fully addressed by existing empirical supported treatments, such as incorporating techniques aimed at addressing interpersonal problems and personality disorder features into existing treatment delivery. We adapted Metacognitive Interpersonal Therapy, a psychological intervention supported by evidence for treating personality disorders and integrated it with existing CBT techniques for eating disorders (MIT-ED). MIT-ED targets aspects of ED that are not included in the transdiagnostic CBT-E model such as poor metacognition, or maladaptive interpersonal schemas. This is a pre-registered (Protocol number: 0000781) pilot randomized clinical trial aimed at assessing acceptability and feasibility of MIT-ED and establishing preliminary evidence of effectiveness for future larger studies. Twenty patients (10 in each arm) will be randomized to 20 sessions of individual psychotherapy, either MIT-ED or CBTE. Repeated follow-ups will be collected up to 24 months. Participants are recruited at a private outpatient clinic for ED treatment. Acceptability will be assessed via session attendance, completion rates and preliminary outcomes. The primary outcome is ED pathology assessed with the Eating Disorder Examination Questionnaire-6. Other ED outcomes assessed will be eating disorder attitudes, clinical impairment and binge eating pathology. Secondary treatment outcomes are anxiety, depression, and global symptomatology. We will also assess emotional awareness, emotion regulation and therapeutic alliance. Based on previous studies of MIT for personality disorders we hypothesize that MIT-ED will be acceptable to patients, evidenced by high treatment adherence and retention. We hypothesize that MIT-ED will be associated with reductions in eating disorder pathology, at least equivalent to CBT-E. Results will be used to inform the study design, sampling, likely effect sizes and choice of outcome measures for future larger trials of MIT-ED in ED samples.