Acute Activity Urges Predict Lower Early Weight Gain During Inpatient Treatment for Anorexia Nervosa.

Early weight gain is a primary goal in the treatment of anorexia nervosa (AN) and associated with more favorable discharge weights and clinical outcomes. Activity urges, that is, a motivational state to engage in activity, have been suspected to delay early weight gain, but their prognostic role remains barely explored. Here, we investigated whether acute (state-like) activity urges at treatment onset would predict within-person weight gain in patients with AN during the initial 2 weeks of inpatient treatment. Adults with AN from an inpatient unit (N = 53) completed an activity urges measure at treatment onset, and weight changes were monitored for the duration of their treatment. Regression analyses, controlling for admission body mass index and other patient variables (i.e., patient age and AN subtype), found that higher state activity urges were associated with lower initial weight gain. Mediation analyses showed that differences in early weight changes further linked higher activity urges at admission to lower discharge weights. An activity urge cutoff value of 2.76 for distinguishing between cases with optimal and suboptimal initial weight gain is proposed. We discuss potential mechanisms of the link between activity urges and early weight gain and the implications of activity urges as a prognostic factor for improving weight restoration during AN treatment.