Drive for thinness provides an alternative, more meaningful, severity indicator than the DSM-5 severity indices for eating disorders.

Objective: To assess an alternative trans-diagnostic indicator for severity based on drive for thinness (DT) for anorexia nervosa (AN), bulimia nervosa (BN), binge-eating disorder (BED), and other specified feeding or eating disorder (OSFED), and to compare this new approach to the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) severity categories for EDs.

Method: A total of 2,811 ED [428 AN-restrictive (AN-R), 313 AN-binge purging (AN-BP), 1,340 BN, 329 BED, 154 OSFED/atypical AN (AT), and 223 OSFED/purging disorder (PD)] patients were classified using: (a) The DSM-5 severity categories and (b) a DT categorisation. These severity classifications were then compared based on ED symptoms, general psychopathology, personality, and impulsive behaviours.

Results: For the DSM-5 categories, most ED patients fell into the 'mild' to 'moderate' categories. Using the DT categories, AN patients were mainly represented in the 'low' DT category, and BN, OSFED/AT, and PD in the 'high' DT category. The clinically significant findings were stronger for the DT than the DSM-5 severity approach (medium-to-large effect sizes). AN-BP and AN-R provided the most pronounced effects.

Conclusion: Our findings question the clinical value of the DSM-5 severity categorisation, and provide initial support for an alternative DT severity approach for AN. HIGHLIGHTS : This study assessed an alternative trans-diagnostic drive for thinness (DT) severity. Category for all eating disorder (ED) sub-types, and then compared this to the Diagnostic and Statistical Manual of Mental Disorders-5 (DSM-5) severity indices for EDs. ED symptoms, general psychopathology, personality, and impulsive behaviours were assessed using both classifications in a total of 2,811 female patients diagnosed with EDs. Clinically significant findings were stronger for the DT than the DSM-5 severity category (medium-to-large effect sizes); there was differentiation of the anorexia nervosa (AN) patients into mainly 'low' DT, and bulimia nervosa (BN) spectrum patients into mainly 'high' DT, vs. most patients were clustered in the 'mild-to-moderate' DSM-5 categories. Our findings provide initial support for an alternative trans-diagnostic DT severity category that may be more clinically meaningful than the DSM-5 severity indices for EDs.