People with anorexia nervosa are often treated in a hospital because

Anorexia nervosa often referred to simply as anorexia, is an eating dysfunction defined by low weight, the anxiety of increasing weight, and a great hope to be thin, occurring in food limitation. Several people with anorexia perceive themselves as overweight even though in actual they are underweight.

thats a little if u want the answer just look it up on google thats what i do haha : )