Characteristics and stability of empirically derived anorexia nervosa subtypes: towards the identification of homogeneous low-weight eating disorder phenotypes.

Anorexia nervosa (AN) is characterized by within-group heterogeneity in symptom presentation, which poses problems for research on etiology and treatment. This study sought to identify homogeneous subtypes of AN, and examine their short-term stability, using empirical methods. A treatment-seeking sample with AN (n = 194) was assessed at baseline and 6- and 12-month follow-ups. Latent class analysis was used to identify homogeneous AN subgroups, and latent transition analysis was used to examine the stability of latent classes. Three low-weight eating disorder classes were identified: 1) fat-phobic restricting (AN-R-FP); 2) fat-phobic binge-eating/purging (AN-BP-FP); and 3) non-fat-phobic restricting (AN-R-NFP). Subtype membership was stable over follow-up, with .68 to .88 probabilities of remaining in the same class from baseline to 6 months, and .87 to 1.00 from 6 months to 12 months. The most common transition pattern was between AN-R-FP and AN-R-NFP (56.8% of transitions); the majority of these participants transitioned from AN-R-FP to AN-R-NFP (n = 20/21). Predictors of latent class membership included lifetime mood and substance use disorder comorbidities, negative temperament, illness duration, and body mass index at treatment presentation. Disinhibition (vs. constraint), history of overweight or obesity, and illness duration decreased the probability of latent transition. Findings support the presence of 3 low-weight eating disorder phenotypes that are highly stable over short-term follow-up. Identification of a stable non-fat-phobic AN phenotype is intriguing and highlights the importance of studying mechanisms that differentiate fat-phobic and non-fat-phobic eating disorders.