It is known that older kittens and adult cats are usually lactose intolerant.

Yet almost all (except just 1) of the cats I've known/had love milk and will steal milk products. And they all get smelly stools or slight diarrhoea after lapping up the milk.

Why is this? Why do they want something they cant digest?

  • 3
    You could ask lactose intolerant people the same thing :D
    – SerenaT
    Dec 22, 2021 at 6:14
  • haha good one. So they (cats) still consider the milk to be food? But isn't it the case that animals are typically instinctually better aware of what foods are bad for them?
    – ahron
    Dec 22, 2021 at 7:12
  • 3
    Imagine a world without humans... then the cat would have no option to get milk after been grown up. So the nature had have no need to train them "eat no milk" because there was no possibility to extinct because of milk consumption... The time since there is milk available is an eyeblink in evolution :) Dec 22, 2021 at 9:22
  • No, animals aren't "instinctually better aware of what foods are bad for them" any more than humans (who are also animals) are. If there's a source of possible nutrition that isn't obviously rotten, animals will eat it. Which is why a cat will eat a loaf of bread when they can't digest grains properly, either. :)
    – Allison C
    Dec 22, 2021 at 15:06
  • 1
    @C.Koca I keep my bread in the refrigerator because my previous cat would pull a loaf from the bottom of the shopping bag and destroy it in the time it took me to take off my jacket. One of my current cats, if given the chance, will also destroy a loaf of bread, and tries to steal my breakfast English muffin every day. Some cats will absolutely eat a loaf of bread.
    – Allison C
    Dec 22, 2021 at 18:21

1 Answer 1


Cats have an instinctive love of milk, because if they didn’t, they’d die as kittens.

After a few months, their mother will wean them, and there is no more milk to be had. Their ability to process it goes away, but there is no need for a second instinct to stop loving milk at that point, which could potentially activate too early and kill them.

Even if they do manage to find some milk as adults, it won’t kill them, which is all that matters to the evolutionary process. A bout of smelly/runny poop just doesn’t matter.

  • That would apply to all mammals, right?
    – ahron
    Dec 24, 2021 at 5:14
  • @Yogesch I would assume so.
    – StephenS
    Dec 24, 2021 at 13:01

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