Symptoms such as diarrhea, bloating, and flatulence after consuming sugar are caused by which of the following?

• A. Hydrolysis of lactose into monosaccharides
• B. Deficiency of brush border oligosaccharidases
• C. Decreased osmotic pressure in the colon
• D. Digestion of starches in the small intestine

Answer: (B)

Sugar digestion depends on brush border enzymes to break disaccharides into absorbable monosaccharides. When these enzymes (such as lactase, a key brush border disaccharidase) are deficient, lactose isn’t split and remains in the intestinal lumen. This undigested lactose pulls water into the gut (osmotic effect) and is fermented by colonic bacteria, producing gas. The combination of watery stool, bloating, and flatulence after consuming sugar is classically seen with lactose intolerance due to a deficiency of brush border oligosaccharidases. For contrast, hydrolyzing lactose would aid absorption rather than cause symptoms; decreased osmotic pressure would lessen water movement and symptoms; and digesting starches in the small intestine isn’t the issue here, since the problem is with a disaccharide in the sugar itself.