Anorexia Nervosa

People suffering from anorexia often perceive themselves as overweight, although in reality, they are underweight.

An excerpt from the article 21 facts about Anorexia Nervosa

These individuals also often deny that they have a problem with low weight. They may weigh themselves frequently, eat small portions, and only certain foods. Some exercise excessively, force themselves to vomit, or use laxatives to lose weight and control their appearance.