Abstract
ObjectiveUnderstanding the mechanisms of action of psychological treatments is a key first step in refining and developing more effective treatments. The present study examined hypothesized mediators of change of enhanced cognitive behavior therapy (CBT‐E) and interpersonal psychotherapy for eating disorders (IPT‐ED).MethodA series of mediation studies were embedded in a randomized controlled trial (RCT) comparing 20 weeks of CBT‐E and IPT‐ED in a transdiagnostic, non‐underweight sample of patients with eating disorders (N = 130) consecutively referred to the service. Three hypothesized mediators of change in CBT‐E (regular eating, weighing frequency, and shape checking) and the key hypothesized mediator of IPT‐ED (interpersonal problem severity) were studied.ResultsThe data supported regular eating as being a mediator of the effect of CBT‐E on binge‐eating frequency. The findings were inconclusive regarding the role of the other putative mediators of the effects of CBT‐E; and were similarly inconclusive for interpersonal problem severity as a mediator of the effect of IPT‐ED.DiscussionThis research highlights the potential benefits of embedding mediation studies within RCTs to better understand how treatments work. The findings supported the role of regular eating in reducing patients' binge‐eating frequency. Other key hypothesized mediators of CBT‐E and IPT‐ED were not supported, although the data were not inconsistent with them. Key methodological issues to address in future work include the need to capture both behavioral and cognitive processes of change in CBT‐E, and identifying key time points for change in IPT‐ED.
Highlights
interpersonal psychotherapy for eating disorders (IPT-ED): Understanding how psychological treatments work provides one of the strongest foundations for enhancing their potency (Kazdin & Nock, 2003)
Full model outputs for all multilevel modeling and structural equational modeling analyses are included in the Supporting Information
Regular eating showed a greater weekly increase in cognitive behavior therapy (CBT-E) compared to IPT-ED, stabilizing around Week 3 of treatment
Summary
IPT-ED: Understanding how psychological treatments work provides one of the strongest foundations for enhancing their potency (Kazdin & Nock, 2003) Without such understanding, it is unclear whether they work as hypothesized, or whether only some components are key to helping patients recover, while others are redundant. This problem is acute in treatments that have several components and are implemented in a personalized manner Both cognitive behavior therapy for eating disorders (CBT-ED) and interpersonal psychotherapy for eating disorders (IPT-ED) are evidence-based treatments (Atwood & Friedman, 2020; NICE, 2017; Norris, Gleaves, & Hutchinson, 2019). They are theoretically distinct and are hypothesized to work in different ways (Murphy, Cooper, Hollon, & Fairburn, 2009). Further work is needed to make these treatments more potent
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