27 Predictors of outcome for cognitive behaviour therapy in binge eating disorder 2 Introduction Binge eating disorder (BED) is characterised by recurrent episodes of uncontrollable overeating without the use of regular, inappropriate compensatory behaviours that are typical for bulimia nervosa (APA, 1994; 2013). Prevalence rates, based on DSM-IV criteria, vary across studies, ranging from 1% to 6.6% in the general population (Grucza et al., 2007; Hoek & Van Hoeken, 2003; Preti, et al., 2009). Among people applying for weight loss treatment prevalence rates are as high as 30% (Niego et al., 2007; Spitzer et al., 1993). BED is frequently associated with obesity. About 70% of BED patients suffer from obesity with a body mass index (BMI) between 30 and 40, whereas about 20% suffer from morbid obesity with a BMI equal to or over 40 (Grucza et al., 2007). Although BED and obesity are associated, individuals with BED differ distinctively from obese people who do not binge. For instance, they report higher calorie intake in non-binge meals, more concerns about shape and weight, more psychiatric problems and lower overall quality of life than obese people without BED (Ahrberg et al., 2011; Grucza et al., 2007; Rieger et al., 2005; Telch & Stice, 1998; Wilfley et al., 2003; Yanovski et al., 1993). Interpersonal psychotherapy (IPT), dialectical behaviour therapy (DBT) and cognitive behaviour therapy (CBT) have all been shown to reduce binge eating substantially, with the latter currently being the treatment of choice for BED (NICE, 2004; Yager, et al., 2012). Abstinence rates for CBT vary across studies and range from 17% to 79% of patients at post-treatment, from 21% to 59% 1 year after treatment and were found to be 36% 3 years after treatment (Grilo et al., 2011; Peterson et al., 2009; Ricca et al., 2010; Wilfley et al., 2002). The positive effects of CBT extend to overconcern with eating, weight and shape and to psychosocial functioning, but CBT does not lead to substantial weight loss (Brownley et al, 2007; Vocks et al, 2010; Wilson et al., 2010; Wilson et al., 2007). Considering the fact that a substantial number of patients do not reach abstinence from binge eating, it is important to establish predictors of treatment response, as this may lead to more targeted and effective interventions. Throughout the years, research on predictors of outcome for BED treatment has focussed on the domains of eating disorder pathology, clinical characteristics and demographic variables. Several recent findings on predictors related to eating disorder pathology indicate that higher baseline levels of both self-reported binge eating frequency and eating disorder psychopathology, as conceptualised by the global Eating Disorder Examination (Questionnaire) score, predict more eating disorder pathology at post-treatment and at longer-term follow-up (Castellini et al., 2011; Grilo et al., 012; Masheb & Grilo, 2008; Thompson-Brenner et al., 2013). However, binge eating frequency at baseline does not predict a diagnostic full recovery (Ricca et al., 2010). In addition, a higher baseline level of body dissatisfaction (i.e. shape and weight concerns) predicts less
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