Lactose intolerance is caused by a deficiency of which enzyme?

• A. Lactase deficiency leading to lactose intolerance.
• B. Amylase deficiency leading to lactose intolerance.
• C. Lipase deficiency leading to lactose intolerance.
• D. Sucrase deficiency leading to lactose intolerance.

Answer: (A)

Lactose intolerance comes from a deficiency of the enzyme that normally breaks down lactose in milk. Lactose is a disaccharide made of glucose and galactose, and the enzyme lactase sits on the lining of the small intestine to split lactose into those two simple sugars for absorption. When lactase is lacking or reduced, lactose remains undigested and moves into the colon, where water is drawn in and bacteria ferment it, causing symptoms like bloating, gas, and diarrhea after dairy consumption. The other enzymes listed target different substances—amylase digests starch, lipase digests fats, and sucrase digests sucrose—so deficiencies in those enzymes wouldn’t specifically cause lactose intolerance.