Weight suppression and body mass index at admission interactively predict weight trajectories during inpatient treatment of anorexia nervosa

Objective: Weight suppression refers to the difference between an individual's current and highest body weight at their current height. Higher weight suppression has been found to predict weight gain in both non-clinical samples and patients with eating disorders. Few studies also have reported interactive effects between weight suppression and current body mass index when predicting weight gain. Methods: In this retrospective study, we analyzed clinical records of inpatients with anorexia nervosa (N = 2191, 97% female) and tested whether weight suppression and body mass index at admission would interactively predict different weight trajectories during treatment. Results: Body weight increased non-linearly during treatment. Higher weight suppression predicted larger weight gain but the nature of this effect depended on body mass index at admission. In patients with a relatively low body weight at admission, those with high weight suppression started at a lower weight and showed a nearly linear and steeper weight gain than those with low weight suppression. In patients with a relatively high body weight at admission, those with high weight suppression started at a similar weight and showed a non-linear and larger weight gain than those with low weight suppression. Conclusion: Findings further support that weight suppression is a robust predictor of weight gain in addition to-and in interaction with-current body weight. As weight suppression can easily be assessed at admission, it may help to anticipate treatment course and outcome in patients with anorexia nervosa.