The goal of this clinical trial is to contribute to the improvement of treatment for eating disorders, by identifying factors that might positively affect treatment outcome.

The main questions it aims to answer are:

1. Do higher levels of self-efficacy positively predict a more positive treatment outcome?
2. Does self-efficacy in itself improve during treatment?
3. Do autonomous motivation, self-esteem and self-efficacy correlate?

These factors will be measured in patients being treated for their eating disorders with Cognitive Behavior Therapy - Ten (CBT-T).

Researchers will administer questionnaires at start, session four and end of treatment.

Participants will:

1. Receive their treatment as usual.
2. fill in questionnaires at the start of treatment, session 4 and end of treatment.

Eating disorders (EDs) are severe psychiatric disorders, characterized by a persistent disturbance of eating which impairs health or psychosocial functioning and causes loss of quality of life. There are several evidence-based forms of treatment, but outcomes are mediocre at best. Previous research found better treatment outcomes with several baseline predictors, such as greater motivation to recover. Research on motivation to change has indicated that autonomous motivated (AM) individuals show better response to treatments for EDs. However, being highly motivated for change, but not experiencing the capacity to really eat more and to deal with the emotions evoked by the process of recovery, might lead to difficulty to change key-behaviors, thus leading to less positive treatment outcome. Several researchers emphasized the importance of self-efficacy as a predictor in eating attitudes and behaviors. This study focuses on whether self-efficacy at the start of treatment is predictive of treatment outcome, measured by the ED-15 questionnaire in patients with an ED. Data will be obtained during CBT-T; a brief (10 sessions) version of cognitive behavioral therapy for eating disorders like BN, BED and OSFED. In CBT-T patients are encouraged, from the start of treatment, to challenge their fears, experience the effect of exposure and motivating them to carry through. This aspect might enlarge patients' experience of self-efficacy. Patients with low level of self-efficacy at start, but higher level of self-efficacy after four sessions, might benefit better from treatment, then patients with lower levels of self-efficacy throughout the treatment. To study this potential effect of treatment on self-efficacy, self-efficacy will be measured at start of treatment, at session four and at the end of treatment.

Self-efficacy, self-esteem and autonomous motivation are concepts that are closely linked to each other. To test if they are positively correlated at start of treatment, measurements covering these concepts will be included at T0.

HYPOTHESES

Primary hypotheses:

Higher levels of self-efficacy will positively predict a more positive treatment outcome as determined by lower eating pathology levels with the ED-15.

Secondary hypotheses:

1. Self-efficacy in itself will improve during treatment.
2. Autonomous motivation, self-esteem and self-efficacy will be positively correlated.

Patients are eligible for participation when they meet the following inclusion criteria:

• Participants must be 18 years or older
• Having an eating disorder diagnosed according to the Diagnostic Statistical Manual (DSM-5)
• Starting CBT-T treatment

Exclusion criteria

• Intellectual disability according to the Diagnostic Statistical Manual (DSM-5) or an IQ below 80
• Inability to speak or read Dutch
• Patients treated under a legal act

(adult) Patients treated for eatingdisorders with CBT-T at Altrecht Eating Disorders Rintveld or at Co-eur.

data will be profided in case of a specific request. Data will be stored anonymously in a database on a special drive for scientific research at Altrecht. Researchers will act according to the Declaration of Helsinki, version 59th WMA General Assembly, October 2008. All study data will be stored in a coded way and the key-to-the-name information will be stored in a separate file which will only be accessible to researchers directly involved in the study. The data will be handled confidently and anonymously and will be stored for at least 15 years, in line with the article 454 section 3 from "Wet op de Geneeskundige Behandelingsovereenkomst - WGBO". Only the researchers who are directly involved in this project will have access to the data. The data will be described at group level. All data will be handled and described within the Altrecht workspace.

for the next 15 years

information can be obtained by contacten the researchers.