(PS6-B43) An Evaluation of Normative Intraday Weight Fluctuations and Correlates to Inform Weight Exposures in Cognitive-behavioral Therapy for Eating Disorders

Cognitive-behavioral therapy for eating disorders involves regular exposure to one’s weight, psychoeducation on normative weight fluctuations, and learning to interpret changes to the number on the scale over time. Treatment manuals suggest that weight fluctuates up to 3 kg (6.6 lbs) over the course of a day (Fairburn, 2008), though we are unaware of research that has validated this value. The current study provides descriptive information about normative intraday weight fluctuations to better inform the interpretation of weight changes in weight exposures. We examined body mass index (BMI), body fat percentage, cognitive restraint, and binge eating as correlates of the degree of intraday weight fluctuation. Undergraduate students (n= 201, 70.15% cisgender female) had height, weight (BMI M(SD)=24.62(7.24) kg/m²) and body fat percentage (M(SD)= 25.62(9.75)%) measured three times over the course of a day. Participants also completed the Eating Pathology Symptoms Inventory (EPSI). Intraday weight fluctuation percentages were calculated as the difference between one’s highest and lowest weight, divided by their average weight across the day (M(SD)= 1.02(0.68)%). On average, weight fluctuated between 0.00% and 2.22% from one’s average weight (95% confidence interval; range: 0.0 – 4.40%; 0 to 5.73 lbs). The degree of intraday weight fluctuations did not differ based on biological sex (t(199)= -0.700, p= .221, d= 0.01). Smaller weight fluctuations were observed with high BMI (r= - .20, p= .004) and body fat percentage (r= -.14, p= .044). For example, someone who is 5’5” and weighs 130 lbs might expect an average fluctuation of 1.40 lbs, whereas somewhere who is 5’5” and weighs 200 lbs might expect a range of 1.11 lbs. EPSI cognitive restraint scores (Β= .03, p= .699) and EPSI binge eating scores (B= -.02, p= .74) did not predict the degree of weight fluctuations above and beyond BMI. These findings suggest that the proposed weight fluctuation of up to 3 kg per day within cognitive-behavioral therapy for eating disorders may be an overestimate relative to normative intraday weight fluctuation, depending upon a patient’s weight. This information may be validating for patients when interpreting changes on the scale over time and allows for data-driven violations of expectancies associated with weight changes in cognitive-behavioral therapy. It may be beneficial for clinicians to consider client’s weight status when providing psychoeducation about normative daily weight fluctuations. Further, the degree of intraday weight fluctuation does not appear to be associated with types of eating pathology, suggesting psychoeducation may be consistent across eating disorder presentations.