Weight Suppression and Body Mass Index Interact to Predict Long-Term Weight Outcomes in Adolescent-Onset Anorexia Nervosa

Research on anorexia nervosa (AN) has emphasized the importance of low absolute body weight, but emerging research suggests the importance of also considering low body weight relative to an individual's highest premorbid weight (weight suppression; WS). Objective: We investigated whether body mass index and WS at lowest weight (BMI-LW and WS-LW) among adolescents with AN predicted BMI at 6-, 10-, or 18-year follow-up, duration of AN, or total eating disorder duration, including time during which criteria were met for bulimia nervosa or eating disorder not otherwise specified. Method: Forty-seven cases of AN identified through community screening in Sweden were included. Weight and height data were collected from medical records, school nurse charts, and study follow-up assessments. Results: Higher WS-LW was associated with higher BMI at 6-year and 10-year follow-up, and this effect was strongest among those with the lowest BMI-LW values. BMI-LW and WS-LW were positively associated with BMI at 18-year follow-up, but there was no significant interaction. There was no significant association between WS-LW and AN duration or eating disorder duration, although eating disorder duration was longer among those with higher BMI-LW, controlling for WS-LW. Conclusions: Absolute and relative weight status interact to predict weight outcomes in AN over the long term. Results suggest that BMI and WS may be more relevant to the prediction of long-term weight outcomes than to the persistence of other eating disorder symptoms.