Meta-analysis of the effects of cognitive-behavioral therapy on the core eating disorder maintaining mechanisms: implications for mechanisms of therapeutic change

Abstract

The original and enhanced cognitive model of eating disorders proposes that cognitive-behavioral therapy (CBT) "works" through modifying dietary restraint and dysfunctional attitudes towards shape and weight. However, evidence supporting the validity of this model is limited. This meta-analysis examined whether CBT can effectively modify these proposed maintaining mechanisms. Randomized controlled trials that compared CBT to control conditions or non-CBT interventions, and reported dietary restraint and shape and weight concern outcomes were searched. Twenty-nine trials were included. CBT was superior to control conditions in reducing shape (g=0.53) and weight (g=0.63) concerns, and dietary restraint (g=0.36). These effects occurred across all diagnoses and treatment formats. Improvements in shape and weight concerns and restraint were also greater in CBT than non-CBT interventions (g's=0.25, 0.24, 0.31, respectively) at post-treatment and follow-up. The magnitude of improvement in binge/purge symptoms was related to the magnitude of improvement in these maintaining mechanisms. Findings demonstrate that CBT has a specific effect in targeting the eating disorder maintaining mechanisms, and offers support to the underlying cognitive model. If changes in these variables during treatment are shown to be causal mechanisms, then these findings show that CBT, relative to non-CBT interventions, is better able to modify these mechanisms.

Keywords:

• CBT
• eating disorders
• mechanisms
• randomized trials
• cognitive model

Notes

1. A previous meta-analysis on the efficacy of any type of CBT protocol for eating disorders analysed CBTs effect “global cognitive symptoms” (Linardon et al., 2017a). In this review, cognitive symptoms were operationalized as any measure, subscale, or construct that assessed a cognitive-related symptom, including attitudes toward eating, weight and shape, body dissatisfaction, thin ideal internalization, and body-related concerns. All of these distinct symptoms were combined into one overall “cognitive symptom” construct. Thus, the effects of CBT on the specific maintaining mechanisms as postulated by the cognitive model have not been examined.

2. No trials on CBT for AN-restricting type met full inclusion criteria. For example, previous trials in this population either did not use a treatment manual based off the Fairburn’s cognitive model (McIntosh et al., 2005; Touyz et al., 2013), or, rather than reporting data for the three maintaining mechanisms, reported global scores on measures of eating disorder psychopathology (Byrne et al., 2017; Zipfel et al., 2014).

3. A few trials reported both the EDE restraint subscale and the Three Factor Eating Questionnaire cognitive restraint subscale. In these instances, only the EDE restraint subscale was analyzed.

4. One trial delivered both an inactive and active comparison group.