The Effects of Autonomy-Enhancing Therapy for Eating Disorders: Protocol for a Single-Case Experimental Multiple Baseline Design

Background: Eating disorders (EDs) remain challenging to treat effectively, with low recovery percentages and high relapse rates. This study protocol explores autonomy-enhancing therapy as a therapeutic adjunct to existing day care treatment in the last phase of treatment. Autonomy-enhancing therapy is aimed at improving autonomy-connectedness: the capacity for self-steering while connected to others, which encompasses self-awareness, sensitivity to others, and the capacity for managing new situations. Higher autonomy-connectedness has been associated with improved ED recovery and lower relapse rates, yet little is known about the effectiveness of autonomy-enhancing therapy in ED populations. Objective: This study examines the effectiveness of autonomy-enhancing therapy in the last phase of a multidisciplinary day care program for anorexia and bulimia nervosa. Methods: A combined single-case experimental design and repeated measures design will be used, involving participants who are in the last phase of day care treatment for anorexia or bulimia nervosa (n=22-30). Participants will receive weekly autonomy-enhancing therapy sessions focused on personal autonomy-related goals and themed group discussions. The primary outcomes (ED symptoms and autonomy-connectedness) will be assessed weekly using the Eating Disorder Examination Questionnaire-Short (EDE-QS) and a short-term version of the Autonomy-Connectedness Scale (ACS-30-ST). Secondary outcomes (depression, anxiety, self-esteem, and quality of life) will be assessed every 3 months using the Symptom Checklist (SCL-90), Rosenberg Self-Esteem Scale (RSES), and World Health Organization Quality of Life-Brief Version (WHOQOL-BREF). Throughout the treatment, we expect improvements in autonomy-connectedness and a decrease in ED symptoms, with autonomy-connectedness mediating treatment success. Additionally, increased self-esteem and quality of life and reduced depression and anxiety are expected after treatment. Visual analysis of the single-case experimental design data and mixed models will be used to evaluate treatment effectiveness, with mediation analyses exploring the role of autonomy-connectedness. Results: Data collection started in March 2024. As of September 2026, 18 participants have completed the study, and 6 are enrolled. An additional 7 participants have been recruited. Data collection is expected to be finalized in February 2027; results are expected to be published in the second half of 2027. Conclusions: This study addresses the need for improved ED treatments by investigating autonomy-enhancing therapy as a potentially valuable adjunct to existing care. Targeting autonomy-connectedness may contribute to reductions in ED symptoms, as well as to broader psychological recovery. Strengths of this study include its practice-based design and the use of a single-case experimental design, allowing a detailed examination of treatment processes. Limitations include the absence of a control condition and the limited follow-up period, which may not fully capture relapse during the period of highest relapse risk. If promising, this study may provide a foundation for future larger-scale controlled studies on autonomy-enhancing therapy in ED treatment.