Baseline Predictors of Adherence in a Randomised Controlled Trial of a New Group Psychological Intervention for People with Recurrent Binge Eating Episodes Associated to Overweight or Obesity

Purpose: Understanding the high rate of treatment adherence in trials of people with eating disorders is important as it can compromise the quality of the trials. In clinical practice, it may also contribute to illness chronicity, relapse, and costs. Thus, we investigated factors associated with adherence to a new treatment HAPIFED, which integrates cognitive behavioural therapy having extended sessions with body weight loss therapy compared to cognitive behavioural therapy with extended sessions alone, for individuals with Bulimia Nervosa or Binge Eating Disorder or other eating disorders comorbid with overweight or obesity. Methods: In total, 98 participants having bulimia nervosa, binge eating disorder and other specified and unspecified eating disorders were recruited with 50 randomised to HAPIFED and 48 to the control intervention CBT-E, all administered in groups of up to 10 participants. An investigator external to the site conducted the random allocation, which was concealed from the statistician involved in the analysis, and known only to the therapists until the finalization of the 12-month follow-up after the end of active treatment. Three scenarios in the timeline treatment of a total of 30 sessions were assessed: 33% or 60% or 75% of presence. Mixed-effects logistic regression analysis was performed to find the correlates of adherence after adjusting for clustering by number of group participants. To account for heterogeneity by types of eating disorders in the sample, the latter variable was considered as a control factor in the models. A subgroup analysis was performed for those with binge eating disorder as this was the largest (N = 66) eating disorder group. Results: None of the six variables—frequency of binge eating episodes, purging, eating disorder symptom severity, weight, illness duration and mental health-related quality of life—significantly predicted adherence at 33%, but longer illness duration predicted higher treatment adherence at both 60% and 75% presence of the interventions. Also for 75% presence, higher body weight predicted lower treatment adherence. For the subgroup analysis, those having higher illness duration had significantly higher odds of treatment adherence for 60% and 75% of the sessions. Conclusions: Higher adherence due to late treatment completion was associated with longer binge eating illness length and a lower body weight. More research is needed to recognize factors that may interfere with engagement in treatments aiming to avoid early dropout.