97 Dialectical behavior therapy compared to cognitive behavior therapy in binge eating disorder 4 the need to further understand the underlying mechanisms of both CBT and BED. Early symptom change was found to consistently mediate better treatment outcomes in CBT (Linardon, de la Piedad Garcia & Brennan, 2017 ) and, in one study, also in DBT-BED (Safer & Joyce, 2011). In CBT, reductions in weight concern (Dingemans et al., 2007) and dietary restraint (Linardon, de la Piedad Garcia & Brennan, 2017) mediated treatment outcome for binge-eating, as did regular eating (Sivyer et al., 2020) in non-underweight eating disorders. Integrating related elements of CBT (e.g. regular eating, decrease body-checking and body-avoidance) into DBT-BED may further improve outcome. Also, subgroups may profit more from one treatment than the other. However, most tested moderator variables did not affect cognitive-behavioral treatment outcome relative to other treatments while some produced conflicting findings (Linardon, de la Piedad Garcia & Brennan, 2017). To BED patients who report greater difficulties in areas that are central to CBT treatment models (i.e. dietary restraint and overvaluation of shape and weight; Fairburn, 2008), CBT may offer incremental benefit over DBT-BED while patients with distinct emotion regulation problems may profit more from DBT-BED. Future research should address these issues. The major difference between this study and the study described in Lammers et al. (2020) is the way assignments to the two treatments were made. In the controlled study, patients were randomized, whereas in this study (with less differences in outcome between CBT+ and DBT-BED) multiple factors were involved in group assignment, including the patients’ preference. This touches upon the possible role of the patients’ active involvement in treatment choice. Shared decision making (e.g. Adams & Drake, 2006) may provide a framework to explore this in the future. To date, research on shared decision making in eating disorders is very limited (Jansingh et al., 2020). This study has several limitations. First, we did not control for treatment dosage. DBT-BED contained less face-to-face contact time per treatment day (2 h per week versus 3.75 h per week), offered only one follow-up session (versus six for some in the CBT+ group) and no group meetings to patients with a partner. This may have disadvantaged the DBT-BED group and limits the reach of our conclusions about the observed differences in outcome. Second, the combination of the large CBT sample (n = 133) and the smaller DBT-BED sample (n = 42) provides adequate power to detect large differences between groups, but limits the ability to detect small or moderate differences. Third, we did not record whether patients in this study had received any prior psychological treatment. This might have helped to provide some insight into whether DBT-BED could be a viable option for patients who have not sufficiently improved with other treatment approaches. Also, because of the controlled study, therapists were supervised and sessions were audiotaped. This may have influenced treatment adherence (allegedly in a positive
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