Lactose intolerant when you shouldn't be

By Razib Khan | December 18, 2011 10:40 am

Milk, it does a body good (or not):

I’ve discussed this before earlier this year, when we got our results back (my husband, children, in-laws, parents, siblings… etc have all done genomic scans), two results came back that surprised us but proved true. My mother-in-law and husband were likely lactose intolerant.

When I pointed that out to my mother-in-law she said “no I’m not.” But then she went on to explain that she never drinks more than a glass of milk because it gives her an upset stomach. Bingo. She learned over the decades that she was indeed lactose intolerant, and shifted behavior because of it, but just didn’t put a name to it.

Later, when I looked at my husband’s profile, sure enough “likely lactose intolerant.” His answer was the same as his mother’s, “no I’m not.” Thing was, in the 15 years I’ve known him he’s had regular stomach problems with no solution.

He probably didn’t make the connection earlier because his mother is of Danish descent (really? Danes aren’t lactose intolerant?) and often dairy in small amounts wouldn’t do a thing, or some products (like yogurt) would have little effect. The problems seemed ‘sporadic’ but frequent. His doctors never suggested lactose intolerance. We could have done a food elimination test, but that was time consuming and very inconvenient. In hindsight we should have done the slog of eliminating foods from the diet…but you know what they say about hindsight? (Or at least the Phantom Tollbooth). He’s the

This is interesting, because I know several people who went through something similar. The vast majority of Northern Europeans are lactose tolerant, at least judging by phenotype and that particular SNP. But, at least ~5% are not. That’s not a small number in absolute terms, and even proportionally it is common enough that if you know 13 random Northern Europeans, there’s a 50% probability that at least one of them is lactose intolerant.

Note: There are other SNPs which likely confer lactose tolerance. And, it seems likely that environmental factors, such as adaptation of your gut flora, also matter in the final phenotype.

  • normann

    That I also am “likely lactose intolerant” was also one of the surprises of my sequencing (the other was between 5% and 8% of my genome identified as Ashkenazi Jewish – I suspect my father’s paternal grandmother, one of whose parents must have been a convert to Catholicism). I have never been a milk drinker, except for a time as part of training regimens (using milk as a substrate for various powders). Since I received this information, I have restricted dairy consumption only to cheese and certain kinds of yogurt (there is a wonderful “Greek” (strained) yogurt imported from Sweden that I eat a lot). The locally produced version (I live in lactose-tolerant, milk-drinking Norway) has powered milk added, which means lactose, which means “digestive and post-digestive” issues, which have otherwise disappeared.

  • Cathy

    Even though I’m not lactose intolerant, I switched over to Lactaid milk because it keeps for TWO MONTHS in the fridge. I don’t really like the taste of milk, so it’s just used for cooking since soy milk doesn’t work so well for that. Whatever witchery they do to it, it’s great. (Interestingly, soy milk gives me a stomachache and I don’t know why.)

  • Grey

    Yes. It never occurred to me that some people couldn’t drink milk until very recently as everyone i grew up with drank gallons of the stuff.

  • Sandgroper

    #1 – I’m finding that I am getting better results using low fat yoghurt than with any of the supplements I have tried, including those for which I used milk as a substrate, particularly if I slug down a yoghurt drink immediately before training.

    #2 – I know someone who gets bloated and then violently ill on soy milk, or soy products of any sort. Northern European ancestry. No idea why.

  • K.Quina

    Im lactose intolerant and my neighbor suggested I try almond milk. It was great however it caused gout. Be careful!

  • omar

    Saw this in my own family. We are cow-herding Gujjars, so the usual thing is to drink a lot of milk and were not attuned to the possibility of lactose intolerance.
    What are the details about the effect of gut flora on lactose intolerance? And is there any evidence that symptomatic lactose intolerance is increasing? Are we seeing more diagnosis or is there a shift in lifestyles/gut flora that is making it show up more?

  • leviticus

    Without testing, one can’t always assume lactose intolerance. Raw milk vs. pasteurized might play a role here. My brother-in-law- like me of mixed British isles and Swiss-German ancestry with a 300 period of duration in US South (influence on gut flora?)- had an awful time with milk until he started drinking raw milk. He noticed an immediate change. Same with my sister. They started drinking raw milk in large quantities. Something nobody in our respective families ever did.

    One can get by in a place like Appalachia and avoid dairy, it’s present, but not omnipresent in local cuisine, unlike Northern Europe. Also, the traditional, local favorite forms of consumption- cottage cheese aka clabber, and buttermilk – are low in lactose.

  • Vitasta

    #6 The effect of gut flora is due to these digesting the undigested lactose literally downstream in the lower gut with all the familiar, attendant symptoms because of this. AFP has a convenient article on it here. Note Table 1 on the causes of secondary hypolactasia.

  • Pohranicni Straze

    My “likely lactose intolerant” result was my biggest surprise from 23andme. While I don’t like milk, I can drink it with no digestive issues at all, and I consume large amounts of other dairy products with no problem. If 23andme ever tests any of the other lactose tolerance SNPs, probably I will turn out to have one of those.

    My wife is another lactose-intolerant individual who can drink milk with no problem. Neither of her parents (respectively Chinese and ethnic Thai) can tolerate milk, but she’s been drinking it since she was a small child, so I guess she never lost her lactase enzymes. Oddly enough, a lot of Thais drink milk now, even though genetically probably 99% of them should be lactose-intolerant.

  • Justin Giancola

    “cottage cheese aka clabber, and buttermilk – are low in lactose.”

    false. compared to what, lactose solution?

    The milk sugar does not bond with the fat, it partners up with protein. The more % fat the milk product, the less lactose; that simple – none of this vodoo. The only exception is some modern whey protein suplements that are lactose free; though I don’t know whether they add lactase or have some separation process.

  • Jim

    I became lactose intolerant after going several months without drinking milk. If I drink milk (any brand) now I get gas so bad that it wakes me up. My genetic profile says that I’m lactose intolerant, so it all adds up… except that I have no problem eating cheese, ice cream, and yogurt (many different brands). Is the lactase in these foods processed in such as way that it is no longer present, at least in a form that causes an irritable bowel?


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About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at


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