**Core Concept**
Bulimia nervosa is a complex eating disorder characterized by recurring episodes of binge eating followed by compensatory behaviors, such as self-induced vomiting, laxative or diuretic abuse, or excessive exercise. This cycle of bingeing and purging can lead to significant physiological and psychological consequences. The disorder is often associated with underlying psychological factors, including low self-esteem, body image distortion, and mood disorders.

**Why the Correct Answer is Right**
The correct association of bulimia nervosa involves the hypothalamic-pituitary-adrenal (HPA) axis, which is dysregulated in individuals with this disorder. The repeated episodes of stress and emotional dysregulation can lead to HPA axis hyperactivity, resulting in elevated cortisol levels. This hypercortisolism can have detrimental effects on various bodily systems, including the cardiovascular, gastrointestinal, and reproductive systems. The HPA axis dysregulation is thought to contribute to the development and maintenance of bulimic behaviors.

**Why Each Wrong Option is Incorrect**
**Option A:** Although depression is a common comorbidity in individuals with bulimia nervosa, it is not the most direct association.
**Option B:** Anxiety disorders are also prevalent in individuals with bulimia nervosa, but they are not the primary association.
**Option C:** Although substance abuse is a potential comorbidity in individuals with bulimia nervosa, it is not the most direct association.

**Clinical Pearl / High-Yield Fact**
Individuals with bulimia nervosa often exhibit a distorted body image and engage in excessive exercise as a compensatory behavior, which can lead to electrolyte imbalances and cardiac arrhythmias.

**Correct Answer: C. Electrolyte imbalance**