Childhood body mass index in adolescent-onset anorexia nervosa.

Objective: Although weight history is relevant in predicting eating disorder symptom severity, little is known about its role in the etiology of anorexia nervosa (AN). This study aimed to determine whether BMI or BMI trajectory differed between individuals who later developed adolescent-onset AN and a comparison group of HCs between school grades 1 through 6.

Method: This study was based on longitudinal data that identified 51 adolescents with AN and 51 matched HCs. Cases were identified through community screening in Sweden and included individuals born in 1969 through 1977. Measured weights and heights were retrieved and BMIs and weight trajectories of the AN and HC groups were compared using growth curve analysis. Main outcome measures included measured BMI and BMI trajectories from grades 1-6. Secondary outcomes examined included ponderal index at birth and maternal body weight.

Results: Individuals who later developed AN had higher BMIs than HCs between grades 1 and 6, by an average of 1.42 BMI-units. There was no difference in rate of weight gain between groups. Ponderal index at birth was higher for the AN as compared with HC group. Maternal weight did not differ significantly between groups.

Discussion: These findings, combined with those previously reported on the premorbid BMIs of those with bulimia nervosa, suggest that a predisposition toward elevated premorbid BMIs during childhood characterizes those who later develop anorexia or bulimia nervosa. These findings are consistent with a transdiagnostic perspective and suggest shared risk factors for AN and obesity. © 2016 Wiley Periodicals, Inc. (Int J Eat Disord 2016; 49:1002-1009).