**Core Concept**
Anorexia nervosa is a complex eating disorder characterized by a persistent and intense fear of gaining weight, which leads to restrictive eating habits and significant weight loss. The underlying psychological and physiological mechanisms involve disruptions in appetite regulation, body image distortion, and excessive exercise.

**Why the Correct Answer is Right**
The core features of anorexia nervosa include a distorted body image, an intense fear of gaining weight, and a restrictive eating pattern, which leads to significant weight loss. Individuals with anorexia nervosa often exhibit a rigid and restrictive eating pattern, which can result in malnutrition and electrolyte imbalances. The pathophysiology of anorexia nervosa involves alterations in the hypothalamic-pituitary-adrenal (HPA) axis, leading to changes in cortisol and leptin levels, which further exacerbate the disorder.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not accurately describe the characteristic features of anorexia nervosa.
**Option B:** This option is incorrect as it is more characteristic of bulimia nervosa, which involves recurrent episodes of binge eating followed by purging or compensatory behaviors.
**Option C:** This option is incorrect as it is more characteristic of obesity, which involves excessive weight gain rather than weight loss.

**Clinical Pearl / High-Yield Fact**
One key aspect of anorexia nervosa is the presence of a "fear of fatness," which can lead to restrictive eating habits and significant weight loss. It's essential to recognize that anorexia nervosa is a treatable condition, and early intervention is crucial to prevent long-term complications.

**Correct Answer: D.**