People with eating disorders like anorexia usually suffer from a protein malnutrition. That's why they tend to be very pale and cold. They also lose muscle and their bones look very prominent.
I think that protein malnutrition is a serious issue because young girls who are still growing and developing often experience these types of eating disorders. A protein deficiency can make them stop growing or can affect their mental function.
A friend of mine had anorexia when we were growing up and she was hospitalized due to starvation and protein malnutrition. The doctor had said that if she hadn't been hospitalized at that time, she would have probably died soon afterward. This is why this issue is so close to my heart.