You're probably lactose intolerant and didn't even know

A pizza commercial with two Japanese guys overly excited about eating pizza.
What's weird about this picture is the Japanese people eating pizza. That they're acting like submorons is standard for Japanese advertising.

I think it's weird that there's a Domino's Pizza delivery place just a few minutes walk from where I live.

Most people wouldn't find that weird. I live in Tokyo, a massive first world metropolis, where pizza is as standard as pizza is in every metropolis. There are pizza places of all kinds all over my neighbourhood.


What makes these pizza places weird to me is the cheese. Most Japanese people, something around 70% of them, should be experiencing considerable discomfort when eating a pizza's worth of cheese. The reason being that around 70% of Japanese people are lactose intolerant, like me. But not only are Japanese people, by all appearances, consuming milk and cheese and other dairy products with reckless abandon, the very concept of lactose intolerance isn't even really known all that well in Japan.

In the English speaking world, if I tell someone I'm lactose intolerant, they at least have a general understanding that it means I can't eat dairy products, though the specifics are usually a little vague. Some people think it means I can't eat eggs, for example, because many include eggs in the concept of "dairy." But even though they don't have all the details right, the term "lactose intolerance" has enough currency in the English language that it's helpful in situations like asking a waiter at a restaurant if something is safe for me to eat.

Not so in Japan. The technical medical term in Japanese, "nyuu tou fu tai shou"(乳糖不耐症), is unfamiliar enough that if I use it, I pretty much always have to clarify the particulars to the point where I might as well not have started with terminology anyway. I've found it's easier to say that I have an "allergy" to milk, but that has it's own problems. Culturally and linguistically, when speaking about milk products, "nyuu sei hin"(乳製品) in Japanese, the emphasis is more or less on the qualitative aspect of milkiness, not on where the milk came from. So people ask if soy milk is also a problem for me. Asking a waiter if something has dairy products in it is usually the start of a long and tedious interaction.

And all of that is weird! Because Japanese people, even more so than where I'm from, are, or at least should be, lactose intolerant! And lactose intolerance, as I've experienced it, is something that isn't easy to ignore. If I drink too much milk, half a cup or more, then my digestive track develops a serious hate for it. If it were just a bout of diarrhea, then maybe that would be tolerable. But it causes painful bloating that takes a frustratingly long time to wind its way through my system. It can ruin a night for me, and I want to know how Japanese people are getting away with it.

Most Japanese people, like me, lack what is called the "lactase persistence gene", which is what allows humans, unlike other animals, to keep drinking milk into adulthood. As far as I know, all other mammals lose the ability to digest their mother's milk after infancy. I've read one theory that suggests that it's advantageous for mammals to lose the ability to drink mother's milk, because the discomfort and reduced benefits is part of what forces them to move on and start seeking nutrition independently from their mother. Maybe, maybe not. The causes are debatable, but what is true is that the normal course of events for all mammals is to not drink milk, mom's or anyone else's, as they grow up.

Humans, though, developed an exception to that rule about an estimated 7,000 years ago. A random mutation among some humans in northern Europe changed the game so that the off switch that stops people from digesting milk is never triggered, and people with that gene can spend their whole lives drinking milk. That's why the gene for allowing drinking milk is called the "lactase persistence gene." It makes you able to keep persisting in making the enzyme in your digestive track necessary to digest milk.

That enzyme in your gut is called "lactase," with an "a," and the substance inside the milk that it breaks down is called "lactose," with an "o." A bit confusing, I know, but those are the words we're stuck with. The point is that in among the protein and calcium and other stuff that makes milk a pretty good food source, it has it's own special kind of sugar, called "lactose." This is where all the problems are. Well... problems if, like me, you're lactose intolerant.

And odds are that you are. The vast majority of the world is. I know it doesn't seem like it, but stay with me. The ability to keep digesting the sugar in milk, to keep making the lactase enzyme for breaking down the lactose sugar, first developed in northern Europe by white people. They also happen to be the people who, as we get closer to more modern times, spread their influence, and their diet, around the world. This is why you get pizza shops in Japan.

As a side note, it seems that in western Saharan Africa, a separate group of people, completely independently, also developed the ability to digest milk sugar. And their genes might have spread a bit, but their culture didn't spread anywhere near as much, so, not to be mean to them or anything, but more for narrative convenience, I'm going to speak mainly about the spread from the European people.

Image: dominos_japan
Spread of the lactase persistence gene across Eurasia and Africa. Image from Nature magazine.

So, anyway, before the cultural spread which brought pizza to places like Japan, there was a much more slow spread of the genes. As you can see in a map from a recent study on lactase persistence, the ability to digest milk sugar spans across the Eurasian continent and down to the tip of Africa. People be fucking, and breeding, all the time, and they do so across tribal lines, enough that these gene even slowly made it from Sweden all the way to Japan. Which actually surprised me a bit, but I guess 6000 years is enough time for lots of migrations and interminglings. Still, it took generations and generations to spread as far as it has, and even after a few millenia, the further away you get from the origin, the less likely it is for locals to have it.

Even among people of northern European decent, it's not the case everyone has it. With my family being entirely from the UK, I'm from a lineage close enough to the source that the ability to eat dairy is the standard, and yet I don't have lactose persistence. It's a recessive gene, but if you recall your Mendel, that doesn't mean it gets wiped out, just that it only manifests when both parents pass it along. My brother is not lactose intolerant, nor are my parents, so that means that while both my mother and father carry the lactase persistence gene, they also both have the non-persistent version, and I drew the short straw and got the crappy one from both of them. Thanks mom and dad.

(Update on March 20, 2014: Recently I had my genome sequenced via the company 23andMe, and actually it turns out that I inherited the lactase persistence gene from both parents. So... turns out mom and dad didn't pass on bum genes.)

The less European you are, the more likely you, like me, didn't get yourself a lactase persistence gene. If you think about the population distribution as you move away from Europe, that's a lot of Chinese and Indian people who are lactose intolerant, just for a start. The majority of the human race is lactose intolerant. That's why I can say that you probably are.

And yet you might not know it. The vast majority of Japanese people don't seem to. What's up with that? When Americans showed up in Japan and said, "hey, have a slice of pizza!" why didn't the Japanese say, "ugh... it tastes okay, but I don't think it's really worth the stomach upsets and all the time in the toilet." We all know that western cultural hegemony can be pretty powerful when it comes to things like food and movies, but I find it hard to believe they could convince people to overcome persistent diarrhea for the joy of having a Pizza Hut in town.

Not that I think the western, mainly American, corporate marketing machine, would have let a little biology get in the way of selling their fast food cheeses around the world. There is, after all, a technological solution. I can buy lactase pills which simply places the missing enzyme into my body, and I can eat all the cheese and ice cream I want if I choose to without any bad effects at all. The pills have an effectiveness of a few hours, so economically speaking they're not a bad deal. It adds maybe 25 cents of cost to a night of me indulging in ice cream or whatever. If it were the case that Japanese people required a little assistance in consuming dairy products then I'm sure that the corporations would have happily provided it. They wouldn't even have to market lactase pills, though they probably could and drive the price down to almost nothing. No, instead, it's possible to simply remove lactase from dairy products. In the west, you can buy lactose free milk, cheese, and ice cream. Lactase is just a sugar, and I'm not totally sure how it's done with any specific product, but essentially all you have to do is add the lactase enzyme in at some stage of the process, and you're good to go. The lactase enzyme takes lactose sugar and breaks it down into more simple sugars, so, as far as I know, you don't even need to add any replacement sugars. Though I imagine lactose free products probably do.

And yet this is not the solution offered in Japan. Lactose free dairy products are completely unavailable here. At least, in all my years of being here, and in spite of looking for them, I have never seen them. You can buy lactase pills over the internet, but they're all brands imported in from places like Canada and the US, and the selection is limited and as a result of the import costs, much more expensive.

There is another technological solution to milk digestion, though, one that is common in Japan, and that is yogurt. Japanese seem to really dig the yogurt, and you can get all sorts of crazy yogurt drinks and deserts and stuff, maybe more than a lot of other countries. Yogurt is a solution to the problem of making milk products digestible for human adults that comes out of the middle east a few thousand years ago. What makes milk into yogurt is bacteria, and how those bacteria do that is by eating the lactose, thus removing it from the end product. So yogurt is safe for me, and for Japanese people, to eat. Is that a part of why yogurt is so big here? Is there a preference for it because it is less associated with any stomach discomfort? Maybe, but it's impossible to say. It could just be a cultural preference.

It could even be that they just love dairy products in general, where yogurt just happens to be a part of it. After all, it's not the case that dairy is limited to American pizza delivery services and fast food joints. Any corner bakery will have tons of cheese drenched buns and pastries. The cheese section at any super market here is as large and varied as anywhere else. I live in an area where there are lots of good restaurants, all of which have plenty of dairy. Among my neighbourhood restaurants there's even a cheese specialty restaurant where the owner will gladly talk your ear off about cheeses while you sample exotic cheeses from around the world. And that's just talking about cheese. Every other dairy product, like ice creams, and whipped creams, and cafe lattes, and whatever else you can think of, are consumed in Japan about as much as anywhere else. Or at least it feels that way to me, as someone who is constantly having to be careful about it.

Image: dominos_japan
The red circle marks where lactose is in a list of ingredients on some crappy junk food in a convenience store.

What really kills me though, is that if you go into any convenience store, and look at the ingredients of many of the junk foods there, particularly chocolate products and baked goods, you will see lactose listed there. Added in on it's own, distilled out from any milk. They could have added any type of sugar, but they chose lactose. From my lactose intolerant perspective, it's mind bending to see this, because that takes it to a new level. It's not that Japanese are somehow putting up with lactose sugars in products where it can't be helped, they're proactively putting it in foods that don't even need it!

It just doesn't add up.

Or at least, it used to not add up for me, and it was something that puzzled and concerned me for a long time, because of its personal implications for me. After all, if it was true that Japanese people are genetically almost all lactose intolerant, and yet able to eat dairy without any concern, is there anything about how that works that I might be able to apply to my situation? I'm not doing too bad since I can have dairy if I really want it by taking one of my lactase pills, and I've come to prefer soy milk with my cereal. But, there are those times when I happen not to have any pills with me, and I'm out somewhere and options are limited... it can be a hassle. Not to mention that if the inevitable zombie apocalypse happens and food sources become scarce, the least restrictions on my diet, the better.

Armchair Science

Here's what's going on when you suffer from the symptoms of lactose intolerance. Lactose sugar is a ‎big fat sugar molecule, and if you have the right enzymes, the lactase enzyme, they break the milk sugar down into smaller sugars which are then in turn absorbed by your body. If you don't have the lactase enzyme, though, then they don't get broken down, and your body can't use them.

Just because those big fat sugar molecules are no good to your body, though, doesn't mean they're no good to anyone, or anything. Your body, especially your digestive track, is full of microbes that live symbiotically with you. There are good ones and neutral ones and sometimes kind of bad ones, though usually if you have a lot of the bad ones you probably don't feel too good. The variety of these microbes is countless, and often scientists make comparisons the variety of life that lives in a place like the Amazon rain forest.

Among that rain-forest sized variety of micro-organisms in your gut can be ones that gladly eat milk sugars if you're not going to. When they do, they digest the milk sugars and then both multiply and excrete their own waste. Thus the bloating and diarrhea. The cause of the symptoms of lactose intolerance is that you just fed a colony of bacteria in your gut who throw a massive party for as long as their are milk sugars to keep them going, and leave you to deal with the after effects.

If it weren't for these bacteria exploiting the presence of milk sugars you can't eat, if it were only that you couldn't digest lactose, then it would pass right through you like some kind of indigestible plastic. It's the bacteria that are the real problem, not the absence of the lactase enzyme. All the lactase enzyme does is break down the lactose sugars before the nasty bacteria can get their evil clutches on it.

When you then take into account that different people have different bacteria in their gut, then it stands to reason people will have different reactions, both qualitatively and quantitatively, which seems to be the case. For example, with me, I seem to be able to eat baked products like cake or bread that have dairy products in them. Something about the cooking process makes it okay for me, and I am only sensitive to dairy in its more raw forms. However, I've known people who can't tolerate lactose even when it's highly processed. I've also known people who are less sensitive than me, where they're only bothered by straight milk, and things like cheese or ice cream don't have much effect. What particular bacteria people have in their bodies varies among individuals and groups of peoples. Thus, it seems that the reason Japanese people don't suffer the ill effects of lactose intolerance as I do even though they are just as lactose intolerant as I am is because they don't have any opportunistic bacteria in their intestines that eat milk sugars. Whereas I do.

(Update on March 20, 2014: As mentioned above, I actually have the lactase persistence gene, which means that I am producing lactase ensyme, but have an aggressive gut bacteria that takes command in spite of that. It could be that this bacteria does not respond to more processed sources of milk which gives my own enzymes time to get to it, and maybe that's why breads and things that include milk don't bother me. In any case, my combination of enzymes and gut bacteria results in my situation, just as everyone will have their own specific balance of circumstance and results.)

Which raises an interesting question of why do I have a colony of aggressively milk-sugar loving bacteria, and why isn't that species of bacteria or anything like it present in Japan?

I think it comes from the fact that I come from a cheese and milk eating culture. In among the northern European stock of people I descended from, dairy products have long been abundant, and so it was an environment in which an intestinal bacteria could evolve to consume them. Even in the gut of a person who has the lactase persistence gene, there is still such an abundance of dairy going through that person that a bacteria could probably get at least some action, just not enough to ever become noticeable to the host human. Every now and again, though, the bacteria will get lucky and find a host like me, who fuck ups now and again and accidentally consumes some dairy, all of it gets handed over to the bacteria, and it's party time. It's probably not the case that the bacteria is specialized wholly for eating milk sugar, just that it can along with whatever else it consumes, and when there isn't a surplus of milk to throw a party with, it ekes out a stable existence without a noticeable effect on the host.

In places like Japan, however, where for the vast majority of time before global sharing of diets and foods, there was very little use of milk, there was also little opportunity for any intestinal bacteria to develop a taste for it. In short, a bacteria in the gut that consumes milk sugar is more likely to develop in a culture that consumes dairy than a culture that doesn't.

The whole science of microbiomes, the ecology of microbes that live in and on our bodies, is fairly new and there's a lot that isn't clear. Like how any particular colony gets in any one person. It's known that the process begins after birth, and your environment effects what microbes will make a home in you. And it can change over time. I didn't become noticeably lactose intolerant until my early twenties. My grandmother became lactose intolerant in her sixties. I think that in both our cases, we stopped producing the lactase enzyme way back when we were toddlers, but it wasn't until later in life that somehow a new microbe got into our system, or maybe an existing one evolved, and our situation changed.

This is also why people who are lactose intolerant exhibit a wide variety of symptoms. We all have the same lack of enzymes, but we probably all have slightly different bacteria that consume the available milk sugars, with different results.

It also means that possibly the situation could be changed. If what I'm saying is right, then it seems likely to me that along with the spread of the lactase persistence gene in Japan, the microbes that exploit dairy will spread as well, making Japanese people more likely to split into noticeably lactose tolerant and lactose intolerant, as it is where I'm from. At the same time, though, technology will factor into it, and it might be possible in the future to kill off the lactose exploiting microbes in people like me, and I could go on to narf down all sorts of dairy products like all the Japanese people do now.

Fitness for the environment

Do I want that though?

Having lactase persistence was a clear advantage in the past, but the environment has changed, and being lactose intolerant may now be an advantage. I know that sounds self serving, but don't take it to mean that I wouldn't like the freedom to be able to just have an ice cream cone whenever I wanted. I'm not saying I have any love for being lactose intolerant on a personal, day to day, level.

What I'm saying is that for the current generation of humans living in developed societies, it's not a lack of food resources that is a problem that needs solving, it's dealing with the over abundance. In first world nations, obesity is more of an issue than starvation. Lactose intolerance has distinctly helped me to keep my weight moderate. Not just because I often pass on eating high calorie dairy products, but also because I avoid associated foods. It's not just that I don't eat the cheese on the pizza, I pass on the whole pizza and all the non-dairy oils and carbohydrates that it includes as well. Also, being lactose intolerant has trained me in how to resist foods in terms of social and psychological conditioning. Partly I developed the ability to say no to things I know I shouldn't eat because I had to say no to dairy products in social and personal settings where temptations abound.

Between the technology to facilitate my dairy intake when I want, and the potential upsides of not having the calories I might have consumed if my diet wasn't restricted, I put my chances of surviving and reproducing on an equal or even better footing than anyone else. Though, that said, my lactose persistence gene carrying brother has three kids and I currently have none, so I'm probably not the best example of the case I'm making. I'm skeptical that there is any causation between lactose intolerance and fear of commitment, but my sample survey of just me suggests some correlation.

Really, though, all I'm saying is that the circumstances of literally only the last one or two generations of humans is so different from the circumstances before to a degree that lactose intolerance is almost certainly irrelevant to any individual's survivability and reproductive chances, so it's not the case that we're on a path where necessarily all humans will end up with the lactase persistence gene. We're more likely on a path where if left unchecked it will have a zero consequence random distribution among all people.

Long before that, though, the technology will almost certainly come along to regulate the microbes in our bodies, so that people like me will be able to consume dairy regardless of the presence of lactase enzymes. You'll know when that technology exists, because I'll be fatter.

Except... Japanese people aren't that fat, so I guess there's still more about how they're eating all this dairy that still needs to be figured out.