# Lactose intolerance in non-human animals **URL:** \ **Category:** Factual Questions\ **Created:** [April 8, 2025, 9:33pm UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806 "2025-04-08T21:33:03Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [April 8, 2025, 9:33pm UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/1 "2025-04-08T21:33:03Z")
Lactose intolerance causes problems for some folks. AIUI, it’s something that develops as/after one ages into adulthood, the theory being that back in the days of cave men, once you were no longer a nursing infant, there wasn’t a compelling reason for your body to continue producing lactase (the enzyme that helps break down lactose during digestion). OTOH, there wasn’t a strong evolutionary advantage to _ceasing_ production of lactase - so some folks develop lactose intolerance, and some folks never do. So what’s the deal with non-human mammals? For any given species, do some individuals become lactose-intolerant later in life? What about non-mammals? Are they generally lactose-intolerant, or not, or does it just vary from species to species? ---
**Author:** ![Great\_Antibob](https://avatars.discourse-cdn.com/v4/letter/g/e47c2d/32.png) [@Great\_Antibob](https://boards.straightdope.com/u/Great_Antibob)\ **Post date:** [April 8, 2025, 9:39pm UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/2 "2025-04-08T21:39:13Z")
Apparently many, if not most, mammals become lactose intolerance after they wean. Even in human beings, lactose tolerance into adulthood is a new phenomenon. IIRC, the mutation only became relatively widespread after the advent of agriculture, particularly after domestication of farm animals. I.e. it became an advantage for at least some of us (not me, I don’t have the genes for it). ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 8, 2025, 9:39pm UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/3 "2025-04-08T21:39:21Z")
Most humans and essentially all nonhuman mammals are lactose-intolerant as adults. ---
**Author:** ![susan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/susan/32/17537_2.png) [@susan](https://boards.straightdope.com/u/susan)\ **Post date:** [April 8, 2025, 9:41pm UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/4 "2025-04-08T21:41:31Z")
Most of my cats have been lactose intolerant. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [April 8, 2025, 9:46pm UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/5 "2025-04-08T21:46:05Z")
> [@Chronos](#): > > Most humans and essentially all nonhuman mammals are lactose-intolerant as adults. If ChatGPT is to be believed, it’s 65% of adults, but this varies widely by ethnicity: - 90-100% of east Asian adults are lactose intolerant. - For west African and mediterranean folks, it’s more like 70-80%. - For northern Europeans, it’s only 5-20%. Is there a good theory about why such a dramatic disparity exists? Does it mean northern Europeans were more into agriculture and making use of animal milk? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 8, 2025, 9:48pm UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/6 "2025-04-08T21:48:35Z")
> [@Machine\_Elf](#): > > Does it mean northern Europeans were more into agriculture and making use of animal milk? And Indians, and Bantu. But yes. Of course, it’s a bit of a chicken-and-egg problem, since there’s no point in raising dairy animals if you’re lactose intolerant, and no point in developing adult lactose tolerance if you don’t have dairy animals. ---
**Author:** ![Great\_Antibob](https://avatars.discourse-cdn.com/v4/letter/g/e47c2d/32.png) [@Great\_Antibob](https://boards.straightdope.com/u/Great_Antibob)\ **Post date:** [April 8, 2025, 9:49pm UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/7 "2025-04-08T21:49:33Z")
Also Evolution in action! The mutation for lactose intolerance is relatively new. Not enough time to spread to all humans or to have independently evolved elsewhere (particularly in places that didn’t raise a lot of dairy animals) ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [April 8, 2025, 10:37pm UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/8 "2025-04-08T22:37:23Z")
> [@Great\_Antibob](#): > > The mutation for lactose intolerance is relatively new. Not enough time to spread to all humans or to have independently evolved elsewhere (particularly in places that didn’t raise a lot of dairy animals) Isn’t it exactly the opposite. Ancient adult humans were mostly all lactose intolerant. Lactose tolerance in adults developed after cattle domestication. ---
**Author:** ![Great\_Antibob](https://avatars.discourse-cdn.com/v4/letter/g/e47c2d/32.png) [@Great\_Antibob](https://boards.straightdope.com/u/Great_Antibob)\ **Post date:** [April 8, 2025, 11:00pm UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/9 "2025-04-08T23:00:39Z")
Yeah, typo. The mutation is for lactose tolerance, not for lactose intolerance (the default). ---
**Author:** ![nearwildheaven](https://avatars.discourse-cdn.com/v4/letter/n/90db22/32.png) [@nearwildheaven](https://boards.straightdope.com/u/nearwildheaven)\ **Post date:** [April 8, 2025, 11:12pm UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/10 "2025-04-08T23:12:07Z")
Cats are DEFINITELY lactose intolerant after they wean (usually, I guess). It’s OK to give a kitten a saucer of milk. It’s usually not such a good idea for adult cats. ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [April 8, 2025, 11:29pm UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/11 "2025-04-08T23:29:06Z")
Can’t you raise dairy animals for children’s nutritional needs, and for processing of milk into low-lactose foods (like yoghurt), creating an environment where there’s a food source potentially available for adults, just waiting for a mutation to occur? ---
**Author:** ![DemonTree](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/demontree/32/8646_2.png) [@DemonTree](https://boards.straightdope.com/u/DemonTree)\ **Post date:** [April 8, 2025, 11:48pm UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/12 "2025-04-08T23:48:14Z")
Yes. Presumably they started out raising animals for meat, and realised at some point that the milk could also be consumed, especially if processed into lower-lactose forms. And lactose intolerant adults can still drink and get nutrition from the fats and proteins in milk, they just can’t digest the sugar, and it will upset their stomach. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 9, 2025, 12:15am UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/13 "2025-04-09T00:15:56Z")
I do wonder why most mammals lose lactose tolerance as adults, though. It seems like “can digest lactose, but only when young, and then it shuts off” is more complicated and error-prone than just “can digest lactose”, and if the metabolic switch flips early, rendering a nursing infant lactose-intolerant, it could be catastrophic. Plus, a predator would presumably ingest some milk if it were to eat the udder or equivalent of a prey animal. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [April 9, 2025, 12:18am UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/14 "2025-04-09T00:18:19Z")
> [@Machine\_Elf](#): > > Is there a good theory about why such a dramatic disparity exists? Does it mean northern Europeans were more into agriculture and making use of animal milk? The answer requires a deep dive into the history of domesticating and milking animals as well as the climate of the setting. The mutation that allows for lactose tolerance appears to have occurred independently at least four times in different parts of the world, as recent studies have found variations in the gene. Here’s a very brief outline. Humans certainly made the connection between animals nursing their young and humans doing so well back into history. Also certainly they understood that animal milk could in emergencies be used to nurse babies and even adults. The problem lay into keeping the milk good in an age before refrigeration. Somewhere along the way, people discovered that fermenting or acidifying milk converted it to longer-lasting forms. Cheese, yogurt, and kefir were some results. Those forms are usually - not always - lower in lactose and/or contain live bacterial cultures that digest lactose. Like many aspects of western culture, these inventions seemed to have first appeared in the Middle East, with the oldest evidence from around 5000 years ago. The area swarmed with cattle, sheep, and goats, milk was plentiful. Exactly how and when that culture moved into northern Europe has been hotly disputed, but it appears to be highly correlated with the spread of Indo-European languages. As milking cultures moved north it spread into areas with true winters that would preserve milk for longer. (There’s a line between the south where oils are common and the north where butter is common.) Isobars, like the ones that show temperatures on weather maps, show that Middle Easterners are around 50% lactose tolerant [note: corrected], with the percentage soaring with latitude until it reaches 90% or more in Scandinavia. (All numbers are approximate because no population-wide studies have been done. The early studies were especially bad, with tiny numbers tested using huge lactose loads. I read them all and I’m still appalled.) The assumption is that being able to freely drink milk or eat milk by-products is advantageous so the mutation, which is recessive, nevertheless spread through populations which depended more heavily on milk. Lactose appears to help digest calcium. The colonization of the rest of the world by northern European nations led to widespread LI that disturbs the nice clean lineage. The difference between the Middle East and East Asia is that east Asians depended more heavily on unmilkable pigs than the milkable meat animals. However, areas which raised large numbers of horses or cattle, like Mongolia and south India, use more milk by-products and so have higher percentages of LI. Nomadic indigenous peoples are less dependent on herd animals and largely have lower levels of LI. Interesting exceptions are peoples just south of the Sahara, who have so few other provisions and so of necessity independently became milk drinkers. The reality is that most people, including those like me who are badly affected by large amounts of lactose, can have small amounts of lactose without ever noticing. Even in western cultures many adults stop drinking milk as adults, so the issue seldom arises. Obviously, extremely sensitive people tend to disproportionately see doctors, get tested, and know if they are LI and should avoid milk. As East Asian countries become westernized milk products have been introduced without causing a diarrhea crisis. tl;dr If your ancestors drank milk you probably can too; if not, probably not. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 9, 2025, 12:28am UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/15 "2025-04-09T00:28:31Z")
> [@Exapno\_Mapcase](#): > > Isobars, like the ones that show temperatures on weather maps, show that Middle Easterners are around 50% lactose intolerant (LI), with the percentage soaring with latitude until it reaches 90% or more in Scandinavia. Did you get this backwards? I would expect lactose tolerance to be higher at higher latitudes, not lactose intolerance. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [April 9, 2025, 12:30am UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/16 "2025-04-09T00:30:31Z")
Yes, I changed the planned sentence halfway through. I’ll go back and note that it’s been corrected. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [April 9, 2025, 1:10am UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/17 "2025-04-09T01:10:44Z")
Thing is the gene emerged on multiple occasions thousands of years before it took off. What triggered its relative explosion in some populations? Not discovering that some farm animals could be milked. Apparently famine and disease. > **[Famine and disease drove the evolution of lactose tolerance in Europe](https://www.ucl.ac.uk/news/2022/jul/famine-and-disease-drove-evolution-lactose-tolerance-europe)** > > Prehistoric people in Europe were consuming milk thousands of years before humans evolved the genetic trait allowing us to digest the milk sugar lactose as adults, finds a new study led by UCL and University of Bristol researchers. Bolding mine. > [@](#): > > … the lactase persistence genetic trait was not common until around 1,000 BC, nearly 4,000 years after it was first detected around 4,700–4,600 BC. … > > … To understand how this relates to the evolution of lactase persistence, the UCL team, led by Professor Thomas, assembled a database of the presence or absence of the lactase persistence genetic variant using published ancient DNA sequences from more than 1,700 prehistoric European and Asian individuals. They first saw it after around 5,000 years ago. By 3,000 years ago it was at appreciable frequencies and is very common today. Next, his team developed a new statistical approach to examine **how well changes in milk use through time explain the natural selection for lactase persistence. Surprisingly, they found no relationship** , even though they were able to show they could detect that relationship if it existed, challenging the long-held view the extent of milk use drove lactase persistence evolution. … > > … Professor Thomas’ team applied indicators of past famine and pathogen exposure into their statistical models. Their results clearly supported both explanations – the lactase persistence gene variant was under stronger natural selection when there were indications of more famine and more pathogens. … Milk was used some by those without lactase persistence just fine in normal times. As long as the person was otherwise healthy and didn’t have too much they would benefit. Too much gave gas and pain but didn’t kill them. But when times were tough, more likely sick and drinking more milk as the crops weren’t doing great … then it made you more likely to die, and your kids less likely to survive without you to provide for them. That’s when the population of those with gene exploded. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [April 9, 2025, 2:30am UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/18 "2025-04-09T02:30:46Z")
The geneticists have been trying to explain the mysteries of lactose tolerance (known as lactose persistence in formal usage) for decades now. Evershed et al. may be right in their understanding. Problem is that the anthropologists have a long history on the subject, too, and frequently look at it in divergent ways, as in this more recent paper by [Stock and Wells](https://watermark.silverchair.com/vfad022.pdf?token=AQECAHi208BE49Ooan9kkhW_Ercy7Dm3ZL_9Cf3qfKAc485ysgAAA0UwggNBBgkqhkiG9w0BBwagggMyMIIDLgIBADCCAycGCSqGSIb3DQEHATAeBglghkgBZQMEAS4wEQQMZdKlhmieIGz5WArOAgEQgIIC-MHTM_h_KSN-xxwr1WAmBrxM0XicBji8uySQk8zOS4N8IzdpTItuUPg4jT71ztX569YiyWxwYF2p869bYprnf_uq3f5M5U5qOPXewNSMLV_KDOIWCmJc0JyC92Wk6oK975fZFob0-aN4X_eZWre_Sz5Q5wURVbSTUlCidmwTpJjkmAeTb-xXp-73RZ_xANTnvgVO7QARLGjRSJFQPHJAyy3Ce-D1mmDqAuQFX9ur-x39Z2i6M9LpK_RLAZPWjqC1J_XPoJ7pCi0W9wlt4Qw_I3XuHv1q1Js24ON2F4B-xvt2hNazt0bKiFxlv6nAHbGYGnb-PD0ls_x4nRPr5Hjh2SxkS-5vLEy68jqrWUS7EYaMtg7yYp70rB19s9PnJeRX2I_jRt5EAeeieEidB3mwU3i2ZN-jqFqNGXAPCwIw23NjIehxx933NitRKruBNXqMxC2mm9FyQvTJBKEcYRN9I-CRJYcZ2pTliXb1wUQZc3rslKJOORNgAVbXqLlgOZcHHc2lQbpF1ga6ZalsCZ-sfyy3aZytg6OlBxFx3ZmuNwwLFVEIKGwn2rTvrHvyyBc9PB2FdqEe2cz19Pqo9kV2p5QnLWMysH7fityoODCuK0OoTXvS3pIt4z8I2bhvM4JacM3GQEfLBh9BVcOrj99CKIP59PHQgnIlAB5wtP6BgEGXRPBK2O_efiRDgsxJRt-a0RtTT90YwupWjr-es2h6Bcs2ksCoN7Tkb1Wwrho72tQw-CoEDSUO0r4rFiVqEuA8IaIVyE67CcEieG9L5HPfpRYV3561q1GbLs9MmgJihs5VC06HubYqcPjuzJ0gtMrQqeL24huASWNco6kezpxeDWtI6fqTQceG9lIP6nez_QsPgJjjuzLLsgce9ItBcBj9BIXlnXtFVPdGjpxNIkWU4z3Vz2DFSu4DUSp_Y7OGxQzKXk3jDNcXj5WPb1UXaj8k3fYT_O-Xeq1E_RG6aR8tnhT7V5Sv3oRyGJdLFVZqr-jih5aeQkyJhcI). Wells is also a professor at UCL, like Thomas, which must make for interesting encounters in the faculty lounge. I’m not qualified to judge the sides here, although I’ll admit my sympathies are with the anthropologists, since the geneticists have a history of overstating the certainty of their conclusions. However, the availability of earlier genetic information has increased by orders of magnitude since I did my research so they may be in the lead today. One major issue that needs to be taken into account is that the mere presence of the gene is weakly correlated with actual behavior. [A different report](https://phys.org/news/2022-07-famine-disease-drove-evolution-lactose.html) on the Nature article has this quote. > Professor Davey Smith added: “Our findings show milk use was widespread in Europe for at least 9,000 years, and healthy humans, even those who are not lactase persistent, could happily consume milk without getting ill. However, drinking milk in lactase non-persistent individuals does lead to a high concentration of lactose in the intestine, which can draw fluid into the colon, and dehydration can result when this is combined with diarrheal disease.” > > “If you are healthy and lactase non-persistent, and you drink lots of milk, you may experience some discomfort, but you not going to die of it. However, if you are severely malnourished and have diarrhea, then you’ve got life-threatening problems. When their crops failed, [prehistoric people](https://phys.org/tags/prehistoric+people/) would have been more likely to consume unfermented high-lactose milk—exactly when they shouldn’t.” I said above that “Also certainly they understood that animal milk could in emergencies be used to nurse babies and even adults.” Milk use during famines was to be expected, although the degree to which they found correlations was interesting. The spread of milk drinking into northern Europe doesn’t seem to fit into this model, however, although I only have access to the abstract not the full article. In the end, I think that we’re trying to explain different aspects of a much larger historical event. Both answers - mine is a much shortened version of what I’ve written elsewhere, mostly based on the anthropologists - might be needed to fully understand what happened at different times in different cultures for different reasons. You’ll notice how heavily larded my post was with qualifiers. I don’t believe anyone has firm answers to most questions. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [April 9, 2025, 2:39am UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/19 "2025-04-09T02:39:43Z")
That exact Davy Smith bit was in the article I linked to! Obviously I am no expert on this. And the study looks primarily at the timing of the rapid expansion of the gene’s prevalence in Europe. It may not be the same explanation in other regions. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [April 9, 2025, 3:16am UTC](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806/20 "2025-04-09T03:16:37Z")
I must be tirederer than I thought. I read the whole article, I swear. Then I checked for other articles and saw that quote I wanted. Really not having a good day. [Next page](https://boards.straightdope.com/t/lactose-intolerance-in-non-human-animals/1016806.md?page=2)