According to the most widely influential treatment guidelines from the National Institute for Health and Clinical Excellence and the American Psychiatric Association, existing evidence for adult AN treatment is weak, and more treatment studies are needed.

The primary objective of this project is to gain knowledge about the effectiveness of CBT-E in the treatment of Anorexia Nervosa (AN). Secondary objectives are to prospectively examine baseline predictors of treatment outcome/drop-out and to examine variables related to treatment process and patient engagement as predictors of outcome/drop-out. Thirdly, in a multidisciplinary approach, to focus on selected pathophysiological mechanisms including disturbed neuropsychological functioning, changes in the gut microbiota, immunological and genetic measures in patients with severe AN in different stages of the disease, and further to investigate to what extent they are related to treatment outcome.

The sample consists of patients aged≥16years with AN admitted to outpatient treatment (CBT-E) at Section for Eating Disorders, Haukeland University Hospital, Bergen, Norway. Outcome measures include BMI, self-reported eating disorder symptoms (EDE-Q), depression (BDI), anxiety (BAI) general psychiatric symptomatology (SCL-90-R, M.I.N.I 6.0), health related quality of life (CIA, RAND-36), physical activity (accelerometers) and neuropsychological functioning. The main measurement points are at the start of treatment, 3months, end of treatment and one year follow-up. Baseline predictors of treatment outcome and drop-out will be examined as well as the association between early adherence, behavioral change, therapeutic alliance and treatment outcome. In addition biochemical, genetic and bacteriological assessments will be conducted.