Naturally Thin, or Anorexic?

How do clinicians distinguish between someone who is naturally thin, and someone who has anorexia? In the DSM-IV, one criteria for anorexia was “amenorrhea,” meaning an abnormal loss of the menstrual cycle. In the DSM-V, this criteria was removed. Now, males can receive the diagnosis, as can females who would otherwise qualify the diagnosis but maintain a normal menstrual cycle.

But what about females who are naturally thin? Females who are naturally thin are underweight for the height and age, but are consuming sufficient calories for their biology. They do not, therefore, suffer from amenorrhea. Under the DSM-IV, the presence of a normal menstrual cycle would have automatically excluded such persons from an anorexia diagnosis. It is possible that with the elimination of this criteria, misdiagnoses naturally thin persons as having anorexia will increase.

The DSM-V attempts to make the distinction between persons who are naturally thin and persons with anorexia based upon behaviors such as restricting food, and fearing weight gain. However, these more objective criteria can be difficult to assess. It is easy to image a naturally thin person whose hobbies include fitness and nutrition being misevaluated as having unhealthy attitudes toward food.

One recent study suggests the use of two blood tests to distinguish between the naturally thin and those with anorexia. First, free-T3, which assesses thyroid function. Second, leptin. Leptin is a hormone that inhibits hunger, and leptin levels are a function of fat mass. If a clinician is ever in doubt about an eating disorder diagnosis, referring to their client to physician who is trained to interpret this test may help avoid a misdiagnosis and waste of treatment resources.