American Board of Internal Medicine (ABIM) Certification Practice Exam

What is a feature of diarrhea due to carbohydrate malabsorption?

1. Increased fat in stool

2. Secretory nature

3. Osmotic nature

4. Impaired motility

The correct answer is: Osmotic nature

Diarrhea resulting from carbohydrate malabsorption is characterized by an osmotic nature. This type of diarrhea occurs when unabsorbed carbohydrates remain in the intestinal lumen, leading to an increase in osmotic load. The presence of these unabsorbed carbohydrates draws water into the intestinal lumen, resulting in loose, watery stools. This osmotic effect typically resolves with fasting, as the absence of carbohydrate intake allows the intestinal contents to clear and for reabsorption to occur. It is a direct consequence of the inability of the intestines to properly absorb certain carbohydrates, which underscores the key role of osmotic forces in this type of diarrhea. In contrast, increased fat in the stool would indicate steatorrhea rather than a specific response to carbohydrate malabsorption. Secretory diarrhea is caused by factors such as infections or toxins that stimulate fluid secretion regardless of the presence of food in the intestine, and impaired motility usually refers to abnormal movement of the gastrointestinal tract that can lead to various types of intestinal symptoms but is not specific to carbohydrate malabsorption. Hence, the osmotic nature of the diarrhea directly reflects the pathogenic mechanism involved in carbohydrate malabsorption.