Lack of insight is a major obstacle in treating patients with anorexia nervosa (AN). In everyday practice, clinicians often describe as delusional AN patients who strongly deny their emaciation.

Despite their diagnostic and clinical significance the level of delusionality of body image beliefs in eating disorders (EDs) has not yet been systematically investigated.

In the present study we assessed for the first time the delusionality of body image beliefs in AN subtypes and BN. We hypothesized that body image beliefs would be delusional only in a subgroup of AN patients and that the patients with restrictive AN would demonstrate the higher levels of delusionality.

We used the Brown Assessment of Beliefs Scale (BABS) to assess the degree of delusionality of body image beliefs in seventy-two participants: 39 with AN and 33 with BN. We also investigated the relationship between body image delusionality and other clinical characteristics in AN.

Only patients with anorexia nervosa (28.8%) had delusional body image beliefs, whereas overvalued ideas appeared to be frequent in both AN and BN. Body image delusionality in AN was associated with restrictive eating pathology, early onset of the disorder and body dissatisfaction.

Results suggest that a delusional variant of anorexia nervosa represents the one end of a continuum of insight among patients with eating disorders. Delusionality constitutes a clinical feature independent of weight loss or eating pathology and thus a distinct component of AN psychopathology, contributing to treatment resistance and illness chronicity.