Why are some people lactose intolerant?

hokay well i was thinking the other day.. (as i do everyday) and well i thought why are some people more lactose intolerant.

my mum is a health know-it-all so i know that as humans we arent supposed to be drinking cows milk for starters

and spare me the genetic story.

i just wanna know is it a problem with the gastric acids in your stomach, or the way you digest things?

thanks yall


Science Advisor
Actually the question is better posed in the opposite: Why are some people lactose tolerant?
The normal situation, or most common at least, in mammals is that we're lactose intolerant as adults.

The reason for lactose intolerance is that the body ceases production of lactase, the enzyme that breaks down lactose (milk sugar). This is what usually happens in mammals as they mature.

Not sparing you the genetic story, the reason for lactose tolerance, is a genetic mutation that disables this shutdown, allowing lactase production to continue into adulthood. It's particularly common in North Europeans, and it's a very recent thing on the evolutionary scale. Only a few thousand years ago most North Europeans were also lactose intolerant.

So if anything we're not 'supposed to' be drinking milk at all, as adults. But it doesn't matter where the milk comes from - lactose is lactose. (although some milks contain less of it)

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