Reciprocal association between session-by-session change in overvaluation of shape and weight and session-by-session change in bulimia nervosa symptoms during cognitive behavior therapies.

Overvaluation of shape and weight (OSW) is supported as an important mechanism underlying improvement in bulimia nervosa (BN) during behavioral therapies (CBTs). It is not yet clear, however, whether changes in OSW temporally precede and prospectively predict changes in BN symptoms during CBTs, limiting the ability to establish causality. The present study is the first to examine whether session-by-session changes in OSW prospectively predict session-by-session changes in BN symptoms during CBTs and clinical outcomes at the end-of-treatment. Participants with BN ( = 44) who received 20 sessions of CBTs completed a brief survey at each session assessing OSW and BN symptom frequency during the past week. Results showed small but significant session-by-session reductions in OSW and BN symptoms during CBTs. Session-by-session improvements in OSW in any given week prospectively predicted reductions in restrictive eating, binge eating, and compulsive exercise in the following week but did not prospectively predict improvements in purging, while improvements in restrictive eating and compulsive exercise in any given week prospectively predicted reductions in OSW in the following week. Average session-by-session change in OSW during treatment was positively associated with remission status and improvements in eating pathology at the end-of-treatment. Changes in OSW temporally precede and prospectively predict changes in BN symptoms during CBTs, and vice versa. These findings may have critical implications for treatment planning and implementation.