"People with anorexia nervosa see themselves as being overly heavy even though they are dangerously thin. The process of eating becomes an obsession. Unusual eating habits develop, such as avoiding food and meals, picking out a few foods and eating these in small quantities, or carefully portioning food. Anorexia generally effects women, and is classified as a common eating disorder." (one source of information you can find here)
Is it coincidence that Paul also mentioned on food in connection with his sober warning that "in later times some will fall away from the faith, paying attention to deceitful spirits and doctrines of demons" (1 Timothy 4:1) ?. He said that one of the evidences of the last days will be those who "advocate abstaining from foods" (v. 3) which are intended to nourish the physical body.
Anorexia is an eating disorder, according to the doctors. But I don't think it has to do with food or desire to remain healthy or have a good body shape. The issue is deception. Some things are confused by Satan or the secularized world inside our minds. We live in the natural world, but we are also involved in spiritual war.