The primary objective of this study is to gain knowledge about the effectiveness of enhanced cognitive behavioral therapy (CBT-E) for anorexia nervosa (AN).

The study will assess the potency of outpatient CBT-E in a sample of patients suffering from AN who are admitted to the Section for Eating Disorders at the Department for Psychosomatic Medicine, Haukeland University Hospital in Bergen, Norway.

Secondary objectives are to (1) prospectively identify baseline predictors of treatment outcome and dropout, (2) determine variables related to the treatment process and patient engagement as predictors of the outcome and/or treatment dropout, and (3) in a multidisciplinary approach, focus on selected pathophysiological mechanisms including changes in the gut microbiota as well as immunological measures in patients with severe AN in different stages of the disease, and determine to what extent they are related to treatment outcome.

Inclusion Criteria:

• patients aged >16 years
• suffering from AN, as diagnosed based on the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-V) and confirmed with a clinical examination.
• either at least one unsuccessful treatment attempt in a secondary health-care service unit or severe AN that is evaluated as not manageable in a secondary health-care service unit.

Exclusion Criteria:

• deemed unsafe to manage on an outpatient basis
• psychiatric comorbidity that precludes a focused eating-disorder treatment, such as psychosis or drug abuse.
• not available to participate during the requested treatment period
• for the analysis of the gut microbiota: patients suffering from inflammatory bowel disease, acute or chronic diarrhea or other bowel disease, treatment with antibiotics during the previous 3 months before stool sampling, or laxative abuse;