The overall aim of this present study is to evaluate Growth Differentiation Factor-15 (GDF-15) and inflammatory cytokines as a possible novel and readily treatable target for the successful therapy of Anorexia Nervosa (AN). Therefore, GDF-15, neuronal and glial damage markers such as Neurofilament light chain (Nfl) and Glial fibrillary acidic protein (GFAP) and cytokines (such as Tumor necrosis factor alpha (TNF-α), Interleukin-6 (IL-6), and Interleukin 1β (IL-1β) levels will be assessed in the serum as well as in the cerebrospinal fluid of patients with diagnosed restrictive AN with and without exercising behavior compared to sex- and age-matched healthy controls to consolidate previous findings and to identify the main site of production of GDF-15 and cytokines in AN.

In addition, assessment of body composition via Dual Energy X-ray Absorptiometry (DEXA )scans and of energy expenditure via indirect calorimetry, respectively, will allow us to correlate GDF-15, Nfl and GFAP and cytokine levels with lean and fat mass measures as well as with energy expenditure, respectively, of AN patients and the matched controls. Overall, this will allow us to comprehensively evaluate GDF-15 and cytokines as possible novel targets for the treatment of AN and to set the basis for a follow up study using available neutralizing antibodies or inhibitors against GDF-15 and the respective cytokines for the treatment of patients with AN, respectively. This will also allow for a more tailored, individualized treatment approach of AN in the future. Our findings will hopefully challenge the viewpoint that AN is a condition which can be controlled by the individual but demonstrate that AN is a biological disease that should be treated by targeting the right biological players in addition to psychiatric treatment.

N=8 adult male and female patients with confirmed diagnosis of anorexia nervosa restrictive type, non-exercising subtype

Inclusion criteria:

• Age 18-60 years
• Written informed consent
• BMI 10-16 kg/m2

N=8 adult male and female patients with confirmed diagnosis of anorexia nervosa restrictive type, exercising subtype will be included in this study.

Inclusion criteria:

• Age 18-60 years
• Written informed consent
• BMI 10-16 kg/m2

N=16 control participants, sex- and age-matched to the individual anorexia nervosa patients.

Inclusion criteria:

• Age 18-60 years
• Written informed consent
• BMI 19-24.9 kg/m2

Exclusion Criteria:

• Use of antibiotics within the last 31 days
• Current illicit drug abuse including daily marijuana or CBD (cannabidiol) consumption (≤ 24 g of alcohol per day allowed)
• Any kind of severe chronic disease other than AN (e.g. active cancer disease)
• Severe renal impairment (e.g. estimated glomerular filtration rate <30 ml/min/m2) if resulting from another disease than AN
• Known liver cirrhosis or other severe liver impairment if resulting from another disease than AN
• Acute upper respiratory tract infection within the last 31 days
• Uncontrolled dysthyroidism
• Uncontrolled hypertension
• Current pregnancy/lactation or current treatment for in vitro fertilization
• Inability to understand the study information, to sign the consent form and to follow the procedures of the study, e.g. due to language problems, psychological disorders, dementia, etc.

Patients with confirmed diagnosis of AN will be recruited via the anorexia outpatient clinic of the Endocrinology Department, University Hospital Basel, headed by Prof. Dr. Katharina Timper and via advertisement. Healthy sex- and age (+/- 3 years of age difference) control participants will be recruited at the medical and endocrinology outpatient clinic of the University Hospital of Basel and via advertisement.