Even though people who suffer from this ailment suffer many physical ailments, the disorder is classified as a mental disorder because much of the problem begins with the patient’s psychology. Before the person begins to control their diet, and in some cases, exercise excessively, they typically experience body dysmorphia (distorted images of the body) and have an irrational fear of weight gain, and this ultimately begins the cycle of self-starvation. The individual begins to develop an extremely unhealthy and irrational fear of food to the point that they begin to stop eating to lose weight or to keep themselves from gaining weight.
The condition is considered a mental disorder because, for one, it is often accompanied by underlying anxiety, depression, mood disorders, personality disorders, and self-harm issues. Then, treatment involves the patient having to be diagnosed and then treated by qualified health professional (usually someone with a psychology or counselling background).
The mental health professional will then have to help the affected patient get over the mental hurdle of eating regular meals in a way that is safe for the person to regain weight and in a way that ensures the person does not relapse.