To go boldly where no scheme has been before: Reconceptualising eating disorder diagnoses

Taking the weight criteria out of anorexia nervosa diagnostic features (Phillipou and Beilharz, 2018) is at first read a preposterous idea. Then I re-read the paper and reconsidered. The authors argue that underweight as a mandatory diagnostic criterion overstates its utility and deemphasises more relevant features associated with severity, outcomes and recovery such as psychopathology and adaptive function.

The authors have been bold and I’d suggest we should be bolder still. First, weight is a criterion for only one eating disorder, anorexia nervosa. All others are diagnosed according to core psychopathologies of disordered eating behaviours and/or cognitions. This causes confusion when people with binge eating and purging may not have a diagnosis of bulimia nervosa if they are underweight. As the authors note, the new ‘atypical anorexia nervosa’ diagnosis is also a state of severe weight loss and dietary restriction similar to anorexia nervosa, but people are at a normal or above normal weight. Does this happen? Well, yes and more often now the average weight of people in Australia is well above a body mass index (BMI; kg/m²) of 25. Thus, many people start weight loss at ever higher BMIs.

I contend that current diagnostic criteria are informed by 19th- and 20th-century conceptualisations of eating disorders and a young, thin, wealthy, female demographic. However, in the 21st century, eating disorders are common in older adults, of either gender, and who may well be from socially disadvantaged groups. Furthermore, a person with an eating disorder is as likely to be overweight as they are to be a normal weight and is very unlikely to be underweight (Hay et al., 2017).

Why not start again and classify eating disorders based on core psychopathologies and common phenotypes? Are there ‘natural groupings’ of people with eating disorders? Studies in community or nonclinical samples have generally confirmed the concept of an eating disorder group but not helped delineate further. For example, Wade et al. (2006) found two of five latent profiles comprised people with eating disorders – one with BMIs 17.9 to <30 of whom 89.0% had a lifetime eating disorder and a second with BMIs ⩾30 of whom 37.0% had a lifetime eating disorder. Those in the high weight group had mostly bulimia nervosa or binge eating disorder while those in the first group included all eating disorders.

Despite the lack of apparent natural groupings, do the Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5) categories inform prognosis or treatments? The answer is partly, e.g., mortality is highest for those with anorexia nervosa, but is yet high for bulimia nervosa and binge eating disorder. People with anorexia nervosa by definition are underweight and thus need re-feeding. But all people with eating disorders will benefit from dietetic advice, and meal planning is part of the ‘trans-diagnostic’ cognitive-behaviour therapy. Another major problem is the diagnostic movement over a person’s lifetime where an individual can experience all three major disorders, and more often than not receive treatment for none (Hart et al., 2011). Poor identification and misperceptions about the defining features of an eating disorder are one factor in this large treatment gap.

One solution is to have a diagnostic category of ‘Eating Disorders’ with a range of specifiers that inform treatment and outcome. Weight, especially underweight, is an obvious specifier. As the Australia and New Zealand Academy for Eating Disorders (ANZAED) (2018) points out, for a person with an eating disorder and high BMI, addressing weight stigma and (I’d add) helping the person navigate the inevitable professional recommendations to lose weight may be very important. A second specifier could be presence of purging with its associated physical consequences and poorer outcomes. This may occur with or without binge or loss of control eating, forms of which may be found in all eating disorders.

In conclusion, I suspect the future is with the US National Institute of Mental Health Research Domain Criteria’s approach. This is to start anew and classify according to phenotypic groups of people with symptoms that are delineated on the basis of common biological/genetic, psychological and other defining features, and that transcend cultural ‘overlays’ such as thin idealisation. To further this, we need longitudinal studies of large community populations, that are representative of the vast majority of people with eating disorders who are not receiving an evidence-based treatment. This would have the added benefit of providing an opportunity to inform the treatment gap and how to close it, thereby reducing the huge community and personal burden from persistent eating disorders. With the government’s Million Minds’ call for research into eating disorders, we can dare to hope for a future with a new understanding of these problems, including but not limited to, how to classify them.