Is there a basis for a weight cut-off point? A large-scale investigation of atypical anorexia and anorexia nervosa subtypes among patients at a residential treatment centre.

OBJECTIVE:There is debate surrounding how to differentiate between anorexia nervosa (AN) and atypical AN (atypAN) as diagnostic entities, and whether a distinction based on BMI is warranted. Better understanding eating disorder (ED) and emotional symptoms across atypAN and AN subtypes [AN-restricting (AN-R), AN-binge/purge (AN-BP)], with and without controlling for BMI, can elucidate how atypAN differs from AN subtypes and whether there is a basis for a BMI cut-off. METHODS:1810 female patients at an ED treatment centre completed intake surveys. ANCOVAs assessed differences across AN-R (n = 853), AN-BP (n = 726), and atypAN (n = 231) groups on ED, depressive, and anxiety symptoms, anxiety sensitivity, experiential avoidance, and mindfulness, with and without controlling for BMI. RESULTS:Relative to AN-R, atypAN and AN-BP groups endorsed significantly higher ED and depressive symptoms, anxiety sensitivity, experiential avoidance, and significantly lower mindfulness (all p < 0.001), but atypAN and AN-BP groups did not differ from one another. When controlling for BMI, all previously significant differences between atypAN and AN-R did not remain significant. CONCLUSION:Individuals with atypAN who have a higher BMI experience more pronounced ED and emotional symptoms, suggesting that relying solely on BMI as a marker of illness severity may be problematic.