Why do some people get lactose intolerance after childhood?
Quick Answer
Many mammals reduce lactase production after weaning, and many humans do the same. Without enough lactase, lactose passes into the colon and can cause gas, cramps, and diarrhea.
The Full Story
Lactase is the enzyme that breaks down lactose, the sugar in milk. In most humans, lactase levels naturally fall after infancy, because milk is no longer the main food source. This is called lactase non-persistence and is the most common pattern worldwide. Some populations evolved lactase persistence, a genetic trait that keeps lactase production high into adulthood, especially in groups with a long history of dairying in Europe, parts of Africa, and the Middle East.
Key Facts
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