Lactose Digestion: Where It Happens & Why Pain Location Varies

Lactose, the primary sugar found in milk and dairy products, is typically digested in the small intestine. The small intestine is responsible for the majority of nutrient absorption, and it contains enzymes called lactase that break down lactose into smaller, absorbable sugars.

However, in some individuals, lactase production may be insufficient or absent, leading to a condition called lactose intolerance. When lactose reaches the large intestine undigested, it encounters bacteria that ferment it, producing gas and causing symptoms such as bloating, abdominal pain, and diarrhea.

The pain experienced with lactose intolerance is often felt in the lower abdomen or around the navel, which is different from the location where lactose would be digested in the small intestine (the upper abdomen). This is because the fermentation of lactose by bacteria occurs primarily in the colon, which is located in the lower abdomen.