One of the things that separates eating disorders from other diagnostic categories is their relative allure--while depression, anxiety, and psychosis, for example, are typically painful, intolerable states, driving people into treatment rather willingly, many who have eating problems are reluctant to seek help. If a friend had entered a depressive episode, I'd have no problem discussing it with her, recommending treatment, etc. It's a little bit different with an eating disorder. I'd probably dance around the topic (yes, this has happened several times before, particularly during my college days, when I first became exposed to the ubiquity of eating disorders), fear that the conversation might jeopardize our friendship, and proceed with calculated caution.
Eating disorders (and, by this, I mean, the clincal conditions of anorexia and bulimia, as well as the omnipresent sub-clinical manifestations of food/weight fixation. . . which, may also meet criteria for other diagnoses, such as Eating Disorder Not Otherwise Specified and Body Dysmorphic Disorder), in this way, look more like alcoholism and substance abuse, than other mental illnesses. Efforts at confrontation are often dismissed or met with failure.
So, why would a woman be so consumed with holding onto her eating disorder? Surely, having an eating problem is not a comfortable way of being in the world. (For just how uncomfortable anorexia can be, read Marya Hornbacher's, Wasted. The author, through her personal memoir, rips every little last ounce of glamour from an eating disorder and hangs it out to dry.)
What comes to mind is the psychological distinction between ego-syntonic versus ego-dystonic conditions. An ego-syntonic disorder is viewed as somehow acceptable and compatible with one's overall self-concept. Ego-dystonic conditions, on the other hand, are behavioral constellations that are inconsistent with your general views about yourself.
Despite the intense pain, secrecy, and obessive quality associated with an eating problem, it's basically ego-syntonic, consistent with a self-image that is negative, punishing, and often quite empty. While treating the eating problem on its own likely will not be met with success, addressing self-esteem concerns may allow a woman to arrive at a place where her eating disorder becomes obsolete.