how does lactose intolerance work and why do only certain people have it
In: Biology
Humans are mammals. That means that when we are babies, our mothers produce milk that we drink. Lactose is a type of sugar found in milk.
In most mammals (and most humans, actually), only babies can digest lactose. As they get older and are weaned off milk, they stop producing the enzyme lactase, which is responsible for digesting lactose. Without lactase, the lactose remains intact until it reaches the intestine where it is literally fermented by bacteria, producing gas; this causes the symptoms of lactose intolerance in humans.
As I said, this is the norm for all mammals, including humans. However, some populations of humans, particularly in Europe and parts of Africa and the Middle East, developed genetic mutations that produce lactase even into adulthood. This is a particularly clever evolutionary trick, as it allows those of us with the mutation to drink milk from domestic animals like cows and goats. However, only around 45% of humans worldwide actually have the mutation, and in some regions like East Asia it is as low as 10%. Even if you belong to a population where lactose persistence is common, it’s not guaranteed you’ll inherit the trait.
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