BIO NMDCAT Carbohydrates
nmdcat.online June 27, 2026

The digestion of lactose in the human small intestine requires the activity of the enzyme lactase. A deficiency in this enzyme leads to lactose intolerance, where undigested lactose

A. Is absorbed directly into the bloodstream and acts as a toxin
B. Is fermented by gut bacteria, producing gases and organic acids that cause gastrointestinal distress
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C. Crystallizes in the kidneys, leading to kidney stones
D. Inhibits the absorption of all other disaccharides

📝 Explanation

In lactose intolerance, lactase (β-galactosidase) is deficient. Undigested lactose passes to the colon, where gut microbiota ferment it. This produces gases like H₂, CO₂, and methane (causing bloating) and short-chain fatty acids, which draw water into the bowel (osmotic diarrhea).

📖 Additional Information

  • Is absorbed directly into the bloodstream and acts as a toxin
  • Is fermented by gut bacteria, producing gases and organic acids that cause gastrointestinal distress
  • Crystallizes in the kidneys, leading to kidney stones
  • Inhibits the absorption of all other disaccharides

In lactose intolerance, lactase (β-galactosidase) is deficient. Undigested lactose passes to the colon, where gut microbiota ferment it. This produces gases like H₂, CO₂, and methane (causing bloating) and short-chain fatty acids, which draw water into the bowel (osmotic diarrhea).

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