Disability. The definition of a disorder is a condition that interferes with "normal function." a bit of fortune cookie wisdom that i like is "you are what you think about most of the time." by this definition, an eating disorder is defined simply by the fact that someone is always pre-occupied by their diet. Medically, though, the definition involves measurable adverse effects on the person's health.
Separate category . The dsm-iv tr (diagnostic manual of the amer psych ass, 4th edition, revised) lists eating disorders as a separate diagnostic category with bulimia nervosa, anorexia nervosa, or not otherwise noted as the three subcategories. See http://behavenet.Com/apa-diagnostic-classification-dsm-iv-tr.