The independent and interacting effects of weight suppression and admission body mass index on treatment weight change in patients with anorexia nervosa or bulimia nervosa.

Objective: Weight suppression (WS) and body mass index (BMI) have predicted weight change in individuals with eating disorders, but the interaction between these variables is understudied. Furthermore, WS is usually measured as absolute WS-the numeric difference between current weight and highest past weight-overlooking the potentially important influence of how much a person weighed at their highest historical weight.

Method: The current study investigated the independent and interacting effects of BMI and two measures of WS at admission on residential treatment weight change. WS measures included absolute WS and the relative WS index, the percentage of total body weight lost from highest past weight. Participants were women with anorexia nervosa (n = 357) or bulimia nervosa (n = 293) who provided complete data, 87% of the eligible treatment sample.

Results: In both diagnostic subsamples, BMI, absolute WS, and the relative WS index all significantly predicted weight change. The interaction between BMI and WS predicted weight change, but only when the relative WS index was used.

Discussion: Results highlight the potential importance of considering an individual's weight and weight history when predicting their treatment weight change and support the importance of utilizing both methods of calculating WS in future research.