**Core Concept:** Anorexia nervosa and bulimia are two eating disorders characterized by abnormal eating habits and disturbances in body image. The key difference lies in the presence of purging behaviors in bulimia.

**Why the Correct Answer is Right:** Anorexia nervosa is primarily characterized by fear of gaining weight, leading to intentional calorie restriction and low body weight. In contrast, bulimia nervosa involves binge eating episodes, followed by compensatory behaviors (purging) to avoid weight gain. Purging behaviors may include self-induced vomiting, excessive exercise, or misuse of laxatives, diuretics, or enemas. These behaviors prevent the individual from gaining weight despite consuming more calories than usual during binge episodes.

**Why Each Wrong Option is Incorrect:**

A. This option is incorrect because anorexia nervosa involves intentional calorie restriction and fear of weight gain, while bulimia nervosa includes binge eating episodes and purging behaviors.

B. This option is incorrect because purging behaviors are a defining feature of bulimia nervosa, not anorexia nervosa. Anorexia nervosa focuses on intentional calorie restriction and fear of weight gain.

C. This option is incorrect as it only describes a symptom of bulimia nervosa (binge eating), not the primary difference between the two disorders.

D. This option is incorrect because the primary difference between anorexia nervosa and bulimia nervosa lies in the presence of purging behaviors (binge eating and purging) in bulimia nervosa, not weight loss.

**Clinical Pearl:** It is essential for healthcare professionals to differentiate between anorexia nervosa and bulimia nervosa to ensure appropriate diagnosis and treatment. Recognizing the presence of purging behaviors in bulimia nervosa can help guide the selection of treatment approaches tailored to the specific disorder.

**Correct Answer:** D. This option highlights the primary difference between anorexia nervosa and bulimia nervosa, focusing on the presence of purging behaviors (binge eating and purging) in bulimia nervosa. By understanding this difference, healthcare professionals can appropriately diagnose and tailor treatment strategies for each disorder.