Abstract:
Purpose: Understanding predictors and moderators of outcomes in trials of people with eating disorders (EDs) is important as it informs person-centred clinical practice. Thus, we investigated pre-treatment clinical features, and mid-therapy decrease in loss of control overeating (LOCE), that may predict and may moderate treatment outcomes to a new manualised psychotherapy (a Healthy Approach to Weight Management and Food in EDs or HAPIFED), for individuals with Bulimia Nervosa or Binge Eating Disorder co-morbid with high body mass index (BMI).
Methods: In the trial 50 and 48 participants were randomised respectively to therapy groups of HAPIFED and the control Cognitive Behaviour Therapy – Enhanced (CBT-E). Assessments included mental health related quality of life (MHRQoL), ED symptom severity (measured with the Eating Disorder Examination questionnaire (EDE-Q)), BMI and LOCE and were at five time points: baseline, mid-treatment, end-treatment, 6 months and 12 months follow-up. Linear mixed and negative binomial mixed effects regressions were performed to investigate predictors and moderators of outcomes. Missing data were multiply imputed assuming intention to treat analysis.
Results: Pre-treatment EDEQ Global scores, MHRQoL and BMI positively predicted ED symptom severity, MHRQoL and BMI respectively up to the end of follow-up (EndFU). Neither purging nor illness duration was a significant predictor of any of the outcomes. A mid- therapy decrease in LOCE (MTLOCE) predicted most outcomes, e.g., increasing MHRQoL (coefficient=0.387, 95% CI 0.0824 – 0.6921, p=0.004) and decreasing frequency of binge-eating episodes (IRR=0.5637, 95% CI 0.3539-0.8977, p=0.0191) and eating disorders symptom severity or EDE-Q (coefficient= -0.65, 95% CI -1.0792 – -0.2217, p=0.0139). For frequency of binge-eating episodes and ED symptom severity as outcomes, the effect of HAPIFED therapy on each was moderated negatively by MTLOCE (for frequency of binge-eating episodes: coefficient= -0.636, SE=0.28, p<0.05, IRR=0.529; for ED symptom severity: coefficient= -0.268, SE=0.13, p<0.05, Cohen’s d= -0.102), but was not moderated by baseline weight/BMI.
Conclusions: A greater decrease by mid-therapy LOCE was associated with improved EndFU MHRQoL and reduced binge-eating episode frequency and ED symptom severity, but no changes in BMI. Moderation of the effect of HAPIFED by MTLOCE decreased EndFU binge-eating episodes and ED symptom severity. A larger longitudinal study with greater participant diversity is recommended to test replicability and generalisability of these findings.
