Starting uses up all the patient's energy, leaving her none for any other activity, including, but not limited to sex. They mean it very sincerely, because the disorder has warped their ability to think and see accurately. An anorectic is in danger of dying. Job One is to restore weight so that his or her body and his or her ability to think clearly, can return to normal. Only at that point will psychotherapy have some chance of succeeding.
Many anorectics know they look skeletal and emaciated.
For the, starvation is a compulsion they can't control, not a plan to become more attractive. Only with abuse. With normal use, by the time food passes in the bowel movement, the body has absorbed most of its calories anyway.