**Core Concept**
Rumination disorder is a feeding disorder characterized by persistent and repetitive regurgitation of food, often accompanied by re-chewing and re-swallowing. This condition is distinct from other eating disorders, such as pica or avoidant/restrictive food intake disorder.

**Why the Correct Answer is Right**
The distinctive feature of rumination disorder is the absence of a known medical or psychiatric condition that could explain the behavior. In contrast to other eating disorders, individuals with rumination disorder do not exhibit a distorted body image or a fear of gaining weight. The pathophysiology of rumination disorder is not fully understood, but it is thought to involve a complex interplay of genetic, environmental, and psychological factors.

**Why Each Wrong Option is Incorrect**
**Option A:** Rumination disorder often co-occurs with other feeding or eating disorders, which is incorrect. While individuals with rumination disorder may have a higher risk of developing other eating disorders, this is not a defining feature of the condition.
**Option B:** Rumination disorder typically begins in infancy or early childhood, which is correct. However, this option is not the correct answer because it is true about rumination disorder.
**Option C:** Rumination disorder is not primarily characterized by a fear of gaining weight, which is correct. However, this option is not the correct answer because it is true about rumination disorder.
**Option D:** Individuals with rumination disorder do not exhibit a distorted body image, which is correct. However, this option is not the correct answer because it is true about rumination disorder.

**Clinical Pearl / High-Yield Fact**
Rumination disorder should be distinguished from other conditions that involve regurgitation of food, such as gastroesophageal reflux disease (GERD) or pyloric stenosis. A thorough medical and psychiatric evaluation is essential to diagnose rumination disorder accurately.

**Correct Answer:** D. Individuals with rumination disorder do not exhibit a distorted body image.