Final answer:
A person with an intense fear of becoming overweight, despite being underweight, is suffering from anorexia nervosa. This disorder involves consumption of very little food and excessive exercise due to a distorted body image and body dysmorphic disorder. Treatment of this disorder is critical to avoid serious health consequences.
Step-by-step explanation:
The eating disorder where a person has an intense fear of becoming overweight despite being underweight is anorexia nervosa. People with this condition consume very little food, are typically obsessed with their diet, and engage in excessive exercise to lose more weight. Those with anorexia nervosa have a distorted body image, often perceiving themselves as overweight even when they are dangerously thin, which is a symptom of body dysmorphic disorder. This misperception and dissatisfaction with their body lead to a drive for thinness that is detrimental to their health.
It is important to distinguish anorexia nervosa from other disorders such as bulimia nervosa, where individuals binge eat and then purge the food, and binge-eating disorder, where individuals compulsively overeat without purging. Due to the various health consequences associated with anorexia nervosa, including malnutrition and severe weight loss, recognition and treatment of this disorder are vital for physical and mental health.