There are 3 types of eating disorders, most relating to overweight issues, but one is an underweight-related disorder.
Anorexia is when a person feels like that they are overweight, yet they are not. They try to eat very little as they believe that they are fat and are trying to lose weight. In reality, they are dangerously underweight and are in a major need of food.
Bulimia is when somebody purposely binge eats to be deliberately sick or to use laxatives (medication which helps to empty the bowels). They do this in order to control their weight.
Binge Eating Disorder
Binge Eating Disorder is when someone believes that they have to eat a very large amount of food or drink in a short space of time, which leads to obesity quite quickly.