Answer: anorexia nervosa.
Explanation:
It can't be malnourishment Malnutrition is a condition that results from eating a diet in which one or more nutrients are either not enough or are too much such that the diet causes health problems. It may involve calories, protein, carbohydrates, vitamins or minerals.
It also can't be just any typical teen because when a child is "coming of age", they actually eat more because they are growing.