Food Science: What is Lactose Intolerance?

More and more of us seem to be succumbing to lactose intolerance these days. And while having a built-in deterrent to eating lots of cheese and ice cream might seem like a boon if you're trying to watch your weight, intolerance to milk products definitely presents its own set of difficulties! So what's going with lactose intolerance and how does it happen in the first place? Read on...

It all comes down to one sugar in the milk called, predictably, "lactose." Young or old, our bodies can't actually absorb lactose as it is, and so we need another enzyme to break it down for us. Without this enzyme, digesting lactose causes gas, bloating, and possibly diarrhea.

This friendly digestive enzyme, "lactase," is present in high levels shortly after birth, but then slowly declines over the next several years. At 2-5 years of age, the levels of lactase reach an average minimum, which is where it pretty much stays through adulthood. The biological reason for this is that humans don't actually need milk after they're weaned and so the body stops producing the enzyme to digest it.

Here's where it gets interesting though! Several thousand years ago, there was a genetic change in some northern European populations that allowed them to continue producing lactase after infancy. In the cold climates where these populations were living, milk was a significant nutritional resource throughout life and the ability to digest it took on evolutionary importance.

This is why people today with northern European ancestry are generally able to easily digest milk and milk products, but people from other parts of the world generally are not. There are obviously exceptions to every rule, but what's important to realize is that the ability to digest milk after infancy is the exception rather than the rule.

Luckily, lactose intolerance doesn't actually mean you can't consume any milk or milk products at all. (Milk intolerance and milk allergies are separate conditions.) Adults with lactose intolerance still have a base level of lactase in their digestive systems, and they can generally consume about a cup of milk per day without any...er...ramifications.

There are also many milk products that don't present digestive difficulties to people with lactose intolerance. Hard or aged cheeses like parmesan and pecorino have little lactose and can be digested easily. Fermented milk products like yogurt and buttermilk can also usually be consumed because they contain a bacteria that assists in lactose digestion.

What has been your experience with lactose intolerance?

Related: On Cooking with Restrictions

(Image: Flickr member Bowena licensed under Creative Commons)

Comments (38)

Lactose intolerance has been on my mind of late, as it seems I've lost some of my capacity for dealing with dairy products. I obviously need to do some research, but is it possible to have lactose intolerance show up in your 30s, after years of consuming dairy products with no problem?

My came on when I was around 21. I started drinking soy milk and carrying Lactaid with me for emergencies. In the beginning, I thought it was the end of the world, now, I just try not to eat caprese, for example, or lots of heavy cream, without some insurance first - it's really not so bad, honestly [but don't tell that to my younger self, I thought it was the end of the world... "coffee without CREAM?!?!"]

I read once that a large percentage of folks who claim lactose intolerance, when objectively tested, aren't really, or aren't nearly as intolerant as they believe. If you think you are, be sure to test yourself regularly, and with a variety of food.
Lactose intolerance is common among those of us with Crohn's Disease, and when my disease was active in my 20's, even a slice of pizza would send me running for the bathroom within a half hour. This really sucked, as you may imagine, especially when hanging out with friends.
Since then, I've slowly reintroduced dairy--first hard cheeses, then yogurt, then ice cream (thank GOD!) and so on, until now, when I eat pretty much any dairy I like. As a foodie, life is much more worth living because of it.
I find lots of people like to blame dairy (or gluten or sugar or...) for not feeling their best, and consider it (whatever "it" happens to be) an evil to be banned from their diets. It's the same mentality that tells people to just take a pill, everything will be fine.
Often, instead of looking for a silver bullet, we instead need to take a look at our entire health--are we getting enough exercise? Are we eating healthy meals, and in appropriate amounts? Are we in a job and/or relationship we enjoy?
Taking a look at the big picure is a lot more complicated and challenging, but in the end, will make us healthier and happier in the long run. Viva pizza!

I've become lactose intolerant this year-and I'm still figuring it out. I would rather work my diet around this fact then buy strange products. A few substitutions:
Milk/Cereal=Yogurt/Wheat berries
Milk=Homemade almond, flax or grain milk
Heavy cream=ground oatmeal

I've been lactose intolerant since my early teens and since I grew up in a house that rarely kept dairy around and never cooked dairy-based meals (and I hate milk), it wasn't a big deal.

Now I live with someone who grew up learning to cook vegetarian Italian food. Put this way: he's a great cook but his style of cooking is almost entirely dependent on cheese and creamy sauces. I've found that I can generally have a few pinches of parmesan or another hard cheese on top of my pasta or mount dishes with butter, but cream-based sauces are totally out as are lasagnas, tortellini and the like. Although we try to work around it (risotto made with broth and wine and a bit of cheese and butter added at the end, non-european cuisines, extra cheese grated on the side for his dish, etc), it is a continual source of stress and conflict.

As for the not being sure? I am guilty of regular experimentation (every time I am presented with a good cheese plate for example) and for awhile worried that I was making a special dietary need where one didn't exist. An encounter with a mustard sauce I didn't realize was cream based as well as the consequences every time I give in to the cheese plate have convinced me otherwise. That said, I'm not that picky when out. If something's not slathered with cheese or rich and creamy, it probably doesn't contain enough dairy to seriously bother me. I'll mention it if someone is cooking but also let them know that unless every single dish is very high in dairy, I'll work my way around it.

I am allergic to dairy and when I state that people say "oh, you're lactose intolerant?" and then I have to correct them.
I was diagnosed 2 1/2 years ago with an allergy to casein, the protein in the cow's milk. I can, however, have goat and sheep milk (hooray for goat cheese!)
Although this seems like a curse more than a blessing, it has been an amazing journey finding different ways to cook with vegan butter, soy milk, soy coffee creamer etc. It is, however, not fun to go out to eat. I have to pull the waitstaff aside and tell them I have a severe milk allergy....

Michelle of Montreal, it IS normal for adults to have problems digesting milk, because as you grow older the amount of enzymes needed to coagulate milk declines. But you still should have no difficulties digesting fermented milk products (cheese, kefir, yogurt, sour cream, etc).

Decreased lactase isn't the only way to become lactose intolerant. Some people have it as a byproduct of Celiac disease. When you lose the microvilli (the wavy absorptive surface of the intestine) then you don't absorb nutrients properly and that leads to intolerance as well. If your disease is in remission after cutting out gluten you may be able to go back to eating dairy again because it was never an enzyme problem but instead a problem with the surface of the intestine. So there is hope for some.

For someone like me who grew up loving dairy to develop lactose intolerance in my early 20s was pretty distressing. No more ice cream or milk on my cereal. I have a pretty good sense of just how much I can have before I start suffering and which dairy products I can eat more of than others. I really love cheese and I've learned I can eat a lot more cheddar than I can cottage cheese.

Sour cream and yogurt can be substituted into a lot of recipes that sometimes turn out even better than the milk version (like mashed potatoes made with sour cream and chicken stock instead of milk).

Lactose intolerance can also happen in conjunction with fructose intolerance, which I have (and which, unlike celiac and lactose intolerance, gets very little press at all). It's also a common misdiagnosis for folks who really have fructose intolerance.

Any lactose intolerants tried raw dairy products (as in, unpasteurized)? Many many people have no reactions to raw milk. You didn't hear about lactose intolerance existing until people started pasteurizing milk. I personally can't tolerate pasteurized milk, but have no issues with raw milk. I stick to raw milk, raw milk cheeses, and fermented dairy products. I prefer to stay away from soy products (soy milk, soy cheeses, etc.) that aren't fermented - they're not great for you.

Lactose intolerance is the worst, especially when you're already a vegetarian or semi-vegetarian. However, I find yogurt, and small quantities of some harder cheeses (e.g. feta, parm) to be okay. The main thing that I find is that not only the obviously things (e.g. rich ice cream, all those yummy triple creme cheeses) are the worst on a lactose-intolerant system, but also that other items that might normally be okay are extremely hard to digest when they're high fat items (full fat Greek yogurt, for example).

eduffey :

I also have a dairy allergy that's difficult to deal with. I've never had it tested but I can tell you that bad things happen when I eat cheese or cream cheese.
What is required to be tested to determine a casein allergy?

Brianna:

My son has a dairy allergy -- you can get a simple blood test (called a RAST test) that will tell you if you have a milk allergy and how that allergy breaks down re: the components of milk. Casein is one of those componants. The test gives you a score (<.35 to 100) that you can track over time to see if/how your sensitivity changes. My son's pediatrician ordered the RAST test -- perhaps your gp could do the same (to save you a trip to an allergist until you have some test results in hand).

Good luck!

Thank you Margaret! I have an appointment with my doctor in two weeks. I will definitely ask for the test!

Risa Kate:
I have just started to drink raw milk (yum!) and have spoken to quite a few people about it. The theory is that people are more allergic to the intracellular cytotoxins and such that the pasteurization process exposes. When milk is pasteurized the normal bacteria break apart exposing everything within to our immune systems, while with raw milk our immune system only sees the extracellular/membrane proteins b/c the bacteria are whole. It makes sense that our bodies would launch a stronger rxn to those things. Dont get me wrong, some people are truely allergic... and that suuucks.

I couldn't digest any dairy or soy products as a baby. That seemed to go away until my early twenties, although the family always teased me about my "nervous stomach". Looking back now, I was always lactose intolerant. Unfortunately, I can't tolerate any goat or sheep dairy products either. And the quadruple whammy? Allergic to soy milk.

I have learned to do a lot with other types of "milk". I use a lot of coconut milk and cream in place of other creams. Cashew milk and almond milk are particularly good in cereal. And I am really excited about all the new Rice Dream products...

At home, it's easy to deal with these issues (disclaimer: I live in San Francisco). Traveling is a separate issue. I often end up asking for vegan options, or asking restaurant staff to make something out of ingredients I find on the menu that are tolerable. They're usually willing to work with me, as long as I present it as an allergy issue. Intolerance gets very little sympathy...

Risa Kate - I've never heard that...I'm curious to try.

I've been lactose intolerant my whole life but they didn't figure it out until I was 12. So my teachers and doctors thought I was making myself sick because I hated school. Good times. I can have hard cheese with hardly any problems, small amounts of milk or ice cream, but cottage cheese makes me want to die. Yogurt helps. Also the more I "cheat" the worse it gets. The lactaid pills work nearly perfectly though, for me.

I'm from a family of Lactoise intollerants (my mom like's to say it's just about the onlt thing we're intollerant of). i found while living in Europe that i had signifficantly less problems with the cheeses there. I think it's because they are made from raw milk. I have been told that when cheese is made from raw milk, the natural bacteria in the cheese eats most of the lactose, while when cheese is made of parturized milk, the cheese makers add both bacteria and sugar to the milk to create the cheese leaving significantly more lactose.

chez shoes:
I am also lactose and fructose intolerant, though if I limit my intake of both I am usually ok. And yes, people don't know about fructose intolerance at all.

I became lactose intolerant after a very heavy gastric infection (gastritt in french or something similar), food poisening from a bad croque monsieur. I think my system just got so stressed and traumatized it now reacts to a lot of things (spring onions also, more than anything, but no other onions).
They say it is not uncommon to get lactose intolerance after a food poisoning, though it is supposed to go away after a couple of years, mine didn't though.

Since childhood I always got a stuffy nose from dairy products, but never any real distress until I hit my late 40's. At that time I began having the other symptoms and coincidentally, was working for a medical group at the time that just happened to have an allergy dept.. I was speaking with the allergist about my symptoms and she did the RAST testing on me, where they take small amounts of blood and titre the offending substances, thereby determining what you are sensitive to and to what degree. The only food that I showed allergy to was dairy - specifically, to Lactoglobulin 1, a protein in cow's milk. I still use dairy, though I do try to use less. For me, the worst offender is the soft cheeses - cottage, ricotta, cream cheese.....

When I eat dairy--any kind in any amount, I get paralyzing stomach pain followed by explosive diarrhea or vomiting. Does this happen to anyone else? I have suspected my allergy is beyond the scope of lactose intolerance, but as I don't mind avoiding dairy products, I haven't had tests done.

my experience with lactose intolerance was amusing, and could have started in childhood (i hated milk, ice cream, cereal with milk etc...and the breakfast standard of milk/cereal often made me vomit) or after food poisoning at 21.

i found an ice cream i craved, but doubled over in pain post ingestion. always cautious after my bout with food poisoning(6 of us, at a party), i was ready to announce to the world that the manufacturing facility was contaminated. aware that i needed calcium, i started drinking milk before going to the gym...needless to say, i had uncontrollable gas that sent others running. finally, my son politely asked: mom, are you "sick" again? i had studied dietetics, and lactose intolerance, and learned the populations that were susceptible...i wasn't in those groups, or so i thought!

well, i decided to do an elimination diet (milk products)...OMG, the gas and pain disappeared!

Growing up I would get a rash and start itching if I had any dairy products. Chocolate would even cause a problem. Soy/rice milk and carob were my only option. Since my husband and I don't want children right now and I am taking the "medicine" to help in that area, I have been able to drink about 1 glass of milk a day to every other day. With the extra hormones I am just intolerant not fully allergic. I agree with 86themilk, it is easier to tell the wait staff that I have allergies to food (pork and dairy) than and intolerance.

My daughter, who is adopted from China, is very lactose intolerant. I learned from her gastroenterologist that most Asian Americans are. He explained that she could take the over the counter, once a day, enzyme to prevent the discomfort milk products caused or she could suffer with the discomfort, without it causing any more serious problems. He also alerted me to the fact that lactose is in many, many food products so a child eating school lunches or snacks at someone's house after school is invariably getting lactose. Easy way to test for lactose intolerance is to try the enzymes and see if they work (or you can spend $1300 for the 5 hour lactose lab test where you drink gunk and breathe into balloon like bags.)

@solveigpus - spring onions probably have a higher fructose content than other onions. I can't eat onions at all without getting symptoms, but I can eat shallots and garlic because of their low fructose content.

@snow: my lactose intolerance isn't quite that bad, but that's *exactly* what happens to me when I ingest even small amounts of fructose. Those are pretty classic "malabsorbtion" symptoms - different than an allergy (no risk of anaphylaxis) but a pretty good sign that you should steer clear of the offending substance!

since this is a site where people generally understand being green and being healthy, i don't mind bringing up the idea of veganism. most people think that vegans are crazy and can't eat anything or enjoy food, but if it's done right it is the complete opposite. when i was a vegetarian i still used dairy products and always felt sick like so many people do. our bodies are made to digest milk from birth because that's what we live off of, and let's remember, we were made to digest our mothers milk, not cows milk. cows milk is intended to beef up a calf. if people would think about this before going for that glass of milk that we 'need' (that is not true at all we get calcium from plenty of other foods, try vegetables!) then not only would the cows benefit, but our health would be so much better as well. cows are put through so much to be milked for humans. MOMS can you imagine being milked for 12 hours a day, standing up, with no room to move or rest? and this amount of milk isnt natural, they are given steroids and hormones to make this produce all that milk. THIS IS THE DAIRY COWS LIFE and a very sad one at that.

if you LOVE milk, whether to drink, bake, or whatever, i would suggest almond milk. it's heaps better than cows milk, and is also a lot healthier than soy or rice milk. it tastes amazing and you will never want cows milk again!

explore other foods than meat and dairy and you will be amazing at how satisfied and healthy you can be!

i've thought i might have a strange version of lactose intolerance- i only have bad reactions to cream or fatty cheeses that have been cooked. is this weird?? i can drink milk all day long and eat cream cheese if it hasn't been cooked, but as soon as it turns into a cheesecake i'm screwed. does anyone know why this is???

Check out the interview with author Nina Planck, who talks about RAW milk and lactose intolerance, over at:

http://www.sustainablesuppers.com/?p=147

thank you northern european ancestors, because I love dairy and have never had a single problem!

I heard somewhere (no idea if it's true) that if you stop eating dairy for a while, your body can become intolerant and you'll have trouble going back to it. does anyone know if there's any merit to this?

Just wanted to chime in and offer a few thoughts...
* An easy, if possibly unpleasant, way to test for lactose intolerance vs. casein problems is to drink several mouthfuls of 100% lactose-free milk (Lactaid makes one). If it sits fine, you are probably just lactose-intolerant. If you have the same problems you've been having, it is probably the casein.

* Cabot brand is very proud of its 100% lactose-free cheeses. Sharp cheddar in general is OK for the lactose intolerant, and Cabot's cottage cheese is the only one I can eat. You can find it at Trader Joe's and health food stores.

* I have noticed that some "full fat" Greek yogurts add cream! That is the problem, not the yogurt. I have learned to read labels even for yogurt thanks to some, er, unpleasant episodes.

* I drank milk growing up but also realize I was pretty unwell most of my life, until learning in my early 30s I was lactose intolerant.

* Lactose intolerance works on a continuum - I can tolerate a little milk in my morning coffee, but that is it for the day. Some can have a slice of cheese on a sandwich.

* For the record, organic lactose-free milk (i.e. Organic Cow) tastes SO MUCH BETTER than larger commercial brands. So if you're going to go that route, pay the extra for organic. So worth it.

* Finally, vegan baking cookbooks are awesome and will remove so much sadness from festive events. My favorite is Vegan Cupcakes Take Over the World.

Foodefafa, I was vegan for 6 years and then started eating dairy again. The first week of the conversion was quite painful, with cramps, stomach ache, and other unpleasant things. The symptoms disappeared after that though and now I digest dairy just fine.

And savyvegan, not all dairy comes from factory farms. It's possible to not be a vegan and still be environmentally conscious. I would imagine that producing all the vegan substitutes that many vegans consume, like Nayonnaise and Earth Balance, takes a lot of resources. Just looks at how long their lists of ingredients are. Not every vegan is healthy and virtuous, just as not all omnivores are mindless animal-haters.

It's not just northern European pastoralists who developed the ability to digest lactose in adulthood; the mutation appears to also have occurred independently in East Africa.

Lactose tolerance is a dominant trait, so it spreads pretty quickly; on the other hand, that means like red hair, lactose intolerance can disappear for a few generations and then pop up again.

Foodefafa--I went for about three weeks consuming almost no dairy because I was going to be traveling soon and didn't want to have to worry about hurrying up and eating what I had before I left so it wouldn't spoil. When I started consuming dairy again--especially milk in my chai, of which I drink a lot--I was very very uncomfortable, and it took me about a week and a half to start digesting it all right again.

everyone really is different. thanks to a nutritionist and a trip to finland (where there is also a very high percentage of lactose intolerance), i can now enjoy sheep/goat products, yogurt, and hard cheeses like cheddar and swiss.

i had a blood test done at the dr's: i had some blood taken upon arriving at the office, ate some dairy, and then had blood taken some time after. i can't remember exactly what was tested for, but seems a simple enough request when at the dr's.

I've been lactose intolerant since I was about 8. At first my parents didn't believe me - they said I was just going through a phase where I didn't want to drink milk - but my symptoms only got worse over time (went from rashes, to extreme stomach cramps, to severe diarrhea) so eventually they had to accept it. Today I can eat hard cheeses without problem, but pretty much any other dairy will make me very sick. Luckily I discovered that I love soy milk and soy ice cream, so I don't have to miss out on much! =)

I'm lactose intolerant and I can't drink Lactaid milk at all. I'm not sure why that is. The pills do nothing for me. Yogurt is no problem, but you have to be careful because many commercial brands are not cultured, or only partly cultured with whey powder added after culturing.

The e. coli in your gut can digest some lactose (one of the reasons even very intolerant people like me can have a little dairy), but eating anything sugary at the same time actually causes the gene that creates lactase to temporarily shut down. Which is why I haven't had an ice cream cone in about seven years, and the last time I did, I really regretted it. I really, really miss ice cream.

I'm surprised that Lactaid is not mentioned anywhere in this article....... I realized I was lactose intolerant maybe 7 years ago, and ever since then I carry Lactaid around in every bag. I have absolutely no reservations about eating dairy products as long as I take a pill with my first bite. I know it works differently for different people, but I think for some (most?) people it can be absolutely life changing.