I'm often asked how one can distinguish between bulimia and purging or binge-purging anorexia nervosa?  What is the difference between them?

Many people say:  “I used to have anorexia and then I developed bulimia” or “She has anorexia and bulima, as well”. This is not accurate, and stems from a common misperception that purging (vomiting) means a patient is bulimic.

So why does it matter?  Diagnosis is important to get right and it matters as much as it matters to differentiate between pneumonia and bronchitis. Both are illnesses of the lung with cough and fever, but each will have a different natural history and hence treatment and prognosis.

OK, so what is the difference?  For one, bulimia nervosa is more prevalent than anorexia nervosa; according to the DSM-IV bulimia has a prevalence of 1-3% in adolescent and young adult females (about 10x the rate found in males). The prevalence of anorexia nervosa is 0.5-1.0%, again according to the DSM-IV.

More Importantly, perhaps, patients with bulimia nervosa tend to be of normal body weight or even higher than normal body weight. Their illness is characterized by episodes of bingeing (eating large amounts of food within a short period of time) followed by compensatory behaviors, typically vomiting.  Patients with bulimia nervosa may occasionally fast for a day or two, but do not have the characteristic long term weight suppression of those with anorexia nervosa.

These distinctions have important implications for treatment and, ultimately, recovery. Therefore a correct diagnosis matters a lot.