For most people, anorexia nervosa and binge eating seem pretty much as opposite as you can get: one involves extreme food denial, and one involves extreme food consumption. There also appear to be preexisting biochemical differences between the two disorders. On the other hand, all types of eating disorders show a correlation with mood and anxiety disorders, and tend to overlap with numerous addictive disorders as well.

Several years ago, Christopher Fairburn proposed a transdiagnostic model of eating disorders, which essentially states that in EDs "shared, but distinctive, clinical features tend to be maintained by similar psychopathological processes" that include low self-esteem, interpersonal difficulties, mood intolerance, and perfectionism. Supporting this theory is the high degree of "switching" from one ED to another, a process formally known as diagnostic migration.

Yet the issue remains: how can two disorders that appear to be almost (ahem) mirror images of each other be the same and yet be different?

In a recent article titled "Affect, cognition, awareness and behavior in eating disorders. Comparison between obesity and anorexia nervosa," a Hungarian psychiatrist looked at differences between AN and obesity. Now, obesity isn't a mental health disorder, nor should it be one; however, binge eating disorder is very real. Since the original text is in Hungarian (with only an English abstract), I don't know whether this is a translation mistake or whether the author is trying to assert that obesity is a mental illness. For the sake of MY arguments and thinking, however, I'm going to think of "obesity" in this article as BED since this appears what the author really should be getting at.

Cserjési makes a cogent point in the abstract:

"Previous studies suggested that emotional disturbances (depression, anxiety and alexithymia), cognitive impairments and distortion of body image are frequently associated with anorexia nervosa. However, obesity is mostly regarded as a weight management problem."

Which is quite true. Although many still view anorexia as a choice and a diet gone too far, there is a slow shift to seeing it as a real mental illness. BED is sadly even further behind.

The results of this study, however, are far more intruiging.

Neuropsychological tasks showed common deficit in attention capacity. Obese patients, both children and adult showed impaired shifting capacity and mental rigidity associated with frontal lobe based executive functions. Obese patients had difficulty in categorizing negative emotions (sadness), anorexic patients in treating happy faces. Obese group evaluated positively the overweight body on the implicit level. Anorexic group did not evaluate positively the ultra thin body. Conclusion: our results suggest that restrictive anorexia nervosa has several common features with anxiety disorder, while obesity can be associated most probably with addictive pathologies.

Impaired set shifting (also called cognitive inflexibility) is now being considered as one of the trademarks of anorexia, as is the relationship between anorexia and anxiety disorders, especially OCD. And Nora Volkow's work out of the National Institute on Drug Abuse has been examining the similarities between obesity, compulsive or binge eating and addiction. (h/t Tiptoe for the last link)

This hasn't totally resolved the issue, as there is plenty of evidence that anorexia shares similarities with addiction and that anxiety is a problem in binge eating. But examining these disorders for their similarities and differences not just in behavior but in underlying neuropsychology will hopefully tell us more about what is really going on and what really causes eating disorders.