Transdiagnostic single-session interventions identify rapid versus gradual responders and inform therapy...

Rapid response to psychological therapy for eating disorders (EDs) is the most robust predictor of good outcomes. However, no research has identified predictors of early response before treatment commences. We address this gap with a proof-of-protocol study in 61 non-underweight adults. We used response to one of the three single-session interventions in the 2-week period between assessment and treatment to classify people as rapid or gradual responders (respectively, ≥30% or <30% decrease in dietary restraint) and stratified them to 10 sessions of lower- (guided online Cognitive Behaviour Therapy [CBT]) or higher-intensity treatment (face-to-face 10-session CBT [CBT-T]), respectively. Thirty patients (49%; no difference between SSIs) were classified as rapid responders in terms of dietary restraint. There was no difference in ED psychopathology between rapid and gradual responders at assessment, but rapid responders had significantly lower levels than gradual responders at pre-treatment (Hedge's g = 1.16 [0.62-1.70]), and session 4 (g = 0.69[0.18-1.20]). There were no significant between-group differences at the end of the treatment or 1-month follow-up, with a significant decrease over time (g = 2.42[1.48-3.37]). Rapid and gradual responders (defined by changes in dietary restraint) can be identified before treatment commences and stratified to an appropriate intensity of treatment, removing differences in treatment outcomes.