Daily instability in body dissatisfaction in individuals with and without eating disorders.

Body dissatisfaction (BD) includes negative thoughts and feelings about one's body shape. Although typically assessed as a trait, BD has been found to fluctuate within a day. The present study examined whether daily instability in BD differs according to trait BD, eating disorder (ED) diagnosis, and engagement in maladaptive exercise. Participants with EDs (n = 166) and controls (n = 44) completed a self-report measure of trait BD and reported BD and engagement in maladaptive exercise five times daily for 14 days as part of an ecological momentary assessment protocol. BD instability was calculated as adjusted mean squared successive difference. On average across assessments, participants with EDs reported a 16% change in their BD ratings between consecutive assessments, which was significantly higher than the 12% change in controls. Trait BD was significantly inversely associated with BD instability in individuals with EDs, but not in controls. BD instability did not differ across ED diagnoses or between days with versus without maladaptive exercise. Findings suggest that BD is a dynamic state that varies within a day, especially in participants with EDs. Further research is needed to clarify whether this heightened instability in BD is a clinically relevant factor underlying ED symptoms.