Understanding Weight Change and Treatment Response in Cognitive Behavioural Therapy for Eating Disorders: A Systematic Review and Examination of CBT-T in Non-Underweight Populations

Cognitive Behavioural Therapy (CBT) is a widely used psychological treatment for eating disorders. It aims to help people by improving patterns of thinking and behaviour related to food, eating and body image. This thesis includes two studies that examine how CBT affects outcomes such as body weight and psychological recovery.
The first chapter reviewed findings from 55 papers examining how body mass index (BMI) changes during and after CBT for eating disorders. CBT was associated with BMI increase, but this depended on a person’s starting weight. People who were underweight showed large and meaningful increases in BMI. In contrast, people who were non underweight showed only small changes in BMI, suggesting that weight is not a useful outcome measure for this group. These changes were maintained after treatment for underweight individuals but were less consistent for those who were not underweight. Differences in research quality and treatment length influenced results, and published studies might overestimate weight gain levels.
The second chapter looked at Brief Cognitive Behavioural Therapy (CBT-T), a short treatment for people with eating disorders who are not underweight. This study included 371 adults and examined both treatment outcomes and what predicts improvement. Results showed that CBT-T was effective in reducing eating disorder symptoms, with many people experiencing meaningful improvements over the course of treatment. However, body weight did not change significantly. The study also found that early improvements in the first few sessions were the strongest predictor of overall success, whilst starting characteristics such as initial symptom severity or weight were of negligible importance.
Overall, the findings suggest that CBT is effective for improving eating disorders symptoms, but that weight change is only relevant in underweight individuals. This highlights the importance of focusing on psychological recovery alongside physical health when assessing treatment success.