In brush border oligosaccharidase deficiency, what is the primary cause of diarrhea and bloating after sugar ingestion?

• A. Osmotically active undigested oligosaccharides
• B. Pancreatic enzyme deficiency
• C. Bile acid malabsorption
• D. Excess protein digestion

Answer: (A)

When the brush border enzymes that digest disaccharides are deficient, ingested sugars stay as undigested oligosaccharides in the intestinal lumen. These undigested carbohydrates raise the luminal osmolality, drawing water into the gut and producing an osmotic diarrhea. Bloating often accompanies this because colonic bacteria ferment the unabsorbed sugars, generating gas. So the key mechanism driving diarrhea and bloating after sugar intake is the presence of osmotically active, undigested oligosaccharides in the lumen. Other options relate to different digestive issues (pancreatic enzyme problems, bile acid malabsorption, or excessive protein digestion) and don’t explain the sugar-specific osmotic effect seen here.