Question

Is an eating disorder that is characterized by an irrational obsession about gaining weight in which the person severly limits the food heor she eats?

Answer 1

The answer would be anorexia

In anorexia nervosa, the person will have a problem with their body image, which makes them feeling fat even though they are skinny. The person will stop eating or severely limit their diet. 
It could be followed by purging, a forceful attempt to throw up the food that has been eaten.