What Is Lactose Intolerance?
Symptoms may include abdominal pain, bloating, diarrhea, gas, and nausea. These symptoms typically start thirty minutes to two hours after eating or drinking milk-based food. Severity typically depends on the amount a person eats or drinks. Lactose intolerance does not cause damage to the gastrointestinal tract.
Lactose intolerance is due to the lack of enzyme lactase in the small intestines to break lactose down into glucose and galactose. There are four types: primary, secondary, developmental, and congenital. Primary lactose intolerance occurs as the number of lactase declines as people age.
Secondary lactose intolerance is due to injury to the small intestine such as from infection, celiac disease, inflammatory bowel disease, or other diseases. Developmental lactose intolerance may occur in premature babies and usually improves over a short period of time. Congenital lactose intolerance is an extremely rare genetic disorder in which little or no lactase is made from birth.
What Happens In My Body If I’m Lactose Intolerant?
When we drink milk or have a milk-based product, lactase in our small intestines breaks down the milk sugar. It then gets absorbed into the body through the small intestines.
But people who are lactose intolerant don’t have it so easy. In them, the lactose doesn’t get broken down. Instead, it goes on to the colon, where it mixes with normal bacteria and ferments. It can cause things like gas, bloating and diarrhea.
There are some steps you can take to test yourself:
- Go without milk or milk products for a couple of weeks.
- If your symptoms disappear, bring dairy products back into your diet a little at a time to take note of how you react.
- If your symptoms continue after cutting out the dairy — or if they return — see your doctor to find out what’s going on.
Who Develops It?
Believe it or not, most adults around the world can’t digest milk — 40% of humans stop producing enough lactase to digest milk between the ages of 2 and 5.
Causes of Lactose Intolerance
There are two main types of lactose intolerance, which have different causes.
Primary Lactose Intolerance
Primary lactose intolerance is the most common. It is caused by a decrease in lactase production with age, so that lactose becomes poorly absorbed (5Trusted Source).
This form of lactose intolerance may be partially caused by genes because it’s more common in some populations than others.
Population studies have estimated that lactose intolerance affects 5–17% of Europeans, around 44% of Americans and 60–80% of Africans and Asians (1Trusted Source).
Secondary Lactose Intolerance
Secondary lactose intolerance is rare. It is caused by illness, such as a stomach bug or a more serious issue like celiac disease. This is because inflammation in the gut wall can lead to a temporary decline in lactase production.
What Are the Symptoms of Lactose Intolerance?
If not managed properly, lactose intolerance can cause severe digestive problems.
The most common symptoms are (3Trusted Source, 7Trusted Source, 8Trusted Source):
- Bloating
- Abdominal cramps
- Gas
- Diarrhea
Some people also experience an urgency to go to the toilet, nausea, vomiting, pain in the lower belly and occasional constipation.
Diarrhea occurs due to undigested lactose in your small intestine, which causes water to move into your digestive tract.
Once it reaches your colon, the lactose is fermented by the bacteria in your gut, forming short-chain fatty acids and gas. This causes bloating, flatulence and pain.
The severity of symptoms can vary, depending on how much lactose you can tolerate and how much you have eaten.
Which Foods Contain Lactose?
Lactose is found in dairy foods and products that contain dairy.
Dairy Foods That Contain Lactose
The following dairy products contain lactose:
- Cow’s milk (all types)
- Goat’s milk
- Cheese (including hard and soft cheeses)
- Ice cream
- Yogurt
- Butter
Foods That Sometimes Contain Lactose
Foods that have some form of dairy as an ingredient may also contain lactose, including:
- Foods made with a milky sauce, like quiche
- Biscuits and cookies
- Chocolate and confectionary, like boiled sweets and candies
- Bread and baked goods
- Cakes
- Breakfast cereals
- Instant soups and sauces
- Processed meats, such as pre-sliced ham or sausages
- Ready meals
- Sauces and gravies
- Potato chips, nuts, and flavored tortillas
- Desserts and custards
Other Names for Added Dairy
You can check if a product contains dairy by looking at the label.
On ingredients lists, added milk or dairy products can be described as:
- Milk
- Milk solids
- Milk powder
- Whey
- Whey protein
- Milk casein
- Curds
- Milk sugar
- Buttermilk
- Cheese
- Malted milk
- Dry milk solids
- Sour cream
- Whey protein concentrate
- Milk byproducts
Don’t be confused if a product contains lactic acid, lactalbumin, lactate or casein. These ingredients aren’t lactose.
Risk factors of Lactose Intolerance
Factors that can make you or your child more prone to lactose intolerance include:
- Increasing age. Lactose intolerance usually appears in adulthood. The condition is uncommon in babies and young children.
- Ethnicity. Lactose intolerance is most common in people of African, Asian, Hispanic and American Indian descent.
- Premature birth. Infants born prematurely may have reduced levels of lactase because the small intestine doesn’t develop lactase-producing cells until late in the third trimester.
- Diseases affecting the small intestine. Small intestine problems that can cause lactose intolerance include bacterial overgrowth, celiac disease, and Crohn’s disease.
- Certain cancer treatments. If you have received radiation therapy for cancer in your abdomen or have intestinal complications from chemotherapy, you have an increased risk of lactose intolerance.
Diagnosis of Lactose Intolerance
A person who has symptoms of lactose intolerance is advised to keep a food diary, listing foods consumed, symptoms, and when they appear, before consulting a physician. This can help with diagnosis.
The doctor may advise the patient to try a lactose-free diet for 2 weeks, to see if symptoms improve. If they do, the individual probably has lactose intolerance.
Some tests can detect an intolerance.
Hydrogen breath test: The patient fasts overnight and then has a lactose solution the following morning. Hydrogen concentrations in exhaled air are measured. High levels of nitrogen indicate lactose intolerance.
Lactose tolerance test: The patient consumes a lactose solution, and then a blood sample is taken to measure glucose levels. If blood glucose levels remain the same, this indicates that glucose has not entered the blood. This is because the lactose has not been successfully broken down into glucose and galactose. In a milk-tolerance test, the person drinks milk instead of a lactose solution.
Stool sample: Lactose tolerance tests and hydrogen breath tests are not suitable for infants, so a stool test may be carried out. High levels of acetate and other fatty acids in the stool can be a sign of lactose intolerance.
Underlying disease or condition: If the symptoms could be due to an underlying cause, such as celiac disease, a small bowel biopsy may be performed. A tissue sample of the small intestinal lining is extracted for testing in a surgical procedure.
Treatment of Lactose Intolerance
The best treatment for a person with lactose intolerance is to avoid foods that contain lactose.
Some people believe that it is more natural not to drink milk because humans are the only mammals that continue to consume milk products after weaning. Lactose intolerance, they argue, is not a problem but a natural occurrence.
People who do not consume milk products may have an intolerance without knowing it, and without it being a problem.
If a person has an underlying condition, however, it is important to seek treatment for the condition.
Avoiding lactose may require some trial and error, but food labeling can help, as a product that contains lactose must be labeled that it contains “milk.”
The Cleveland Clinic suggests following a lactose-free diet for 2 weeks and then reintroducing foods with lactose, to assess tolerance levels. People with an intolerance, they say, may be able to consume 12 grams of lactose at one time without any effect.
How Do I Know If I’m Lactose Intolerant?
Our bodies react to milk in ways that are easily measured. Two common tests for adults are:
- Breath test. This will show if you have high levels of hydrogen when you exhale. If you do, you might be lactose intolerant. That’s because hydrogen is given off when lactose is broken down in the colon. The hydrogen gets taken by the blood up to your lungs, and when you exhale it.
- Blood test. This can show how your body reacts after you drink something with a lot of lactose. However, this test is usually not done.
Doctors can also take a stool sample from babies and young children.
What If I Have It?
You may still be able to eat or drink small amounts of milk. Some people do better if they have their dairy with a meal. And, some dairy products, like hard cheese or yogurt, may be easier to digest.
Also, there are lots of lactose-free dairy products at the supermarket. Or you can take commonly found over-the-counter supplements (like Lactaid) to break down the milk sugars if you still want the real thing.
But if you give up milk completely, you can still get plenty of calcium, vitamin D and other nutrients in a healthy diet.
Instead of milk, you can substitute these foods:
- Almonds
- Dried beans
- Tofu
- Collards
- Kale
- Calcium-fortified orange juice and soy milk
- Fatty fish, like salmon, tuna and mackerel
- Egg yolks
- Beef liver
If you have symptoms of lactose intolerance, see your doctor. And if you’re diagnosed with it, talk with her about how to be sure you’re eating right.
Frequently Asked Questions About Lactose Intolerance
What are Lactose and Lactase?
As a sugar, lactose is part of the carbohydrate family. It’s fairly small and simple compared to the of the other carbohydrates, but not quite simple enough. Each molecule of lactose is made by joining two simpler sugars, glucose and galactose. Digestion makes the lactose usable in the body by splitting it back into these component parts. Digestive enzymes are named for the molecule that they specifically target — that’s why lactose’s enzyme is called lactase. No other enzyme will digest lactose.
What Are the Symptoms from Insufficient Lactase?
Any lactose that doesn’t get digested by lactase stays in your intestines. That triggers any number of events, all of them bad. One of the other important things that intestines do is absorb the water that you take in, either straight or as part of other foods.
Undigested lactose reverses this, actually pulling additional water out of the surrounding tissue into the digestive tract and sluicing the lactose down to our bowels. Speeding this process makes it even less likely that the lactose and lactase will have time to find one another.
Adding insult to injury, the excess water also creates an uncomfortable bloated feeling. In consequence, what reaches the colon is a large volume of lactose-laden water rather than a small volume of semi-dry solid. Trillions of normally beneficial colonic bacteria leap upon the lactose as if it were a gourmet meal, producing bubbles of gas for hours on end until all the lactose is devoured.
Gas and bloating are bad enough, but excess water and gas in the colon create pressure that can lead to an almost immediate need to explosively expel loose, watery stools. Even without diarrhea, the continual production of trapped gas can also produce an accompanying and long-lasting medley of bloating, pain, cramps and borborygmi, those embarrassing rumbling noises from moving gas that make you wonder what in the world is going on inside your body.
Of course, in practice, some people will have minimal symptoms or none at all. Others will suffer through pain and cramps that even a doctor has described as “unbearable.” And these symptoms can start almost immediately and last for hours, even days, or they can hold off for the ten to twelve hours it takes food to reach the colon.
Everybody’s symptoms are their own and may vary from meal to meal. You have to learn how to read your own body. Note that all these symptoms are lower intestinal complaints. If you have vomiting, burping, heartburn, reflex, or any other true stomach problems, you need to look elsewhere for the cause.
How Can I Tell if I Have LI?
There are very good tests for LI. The best one is called the Breath Hydrogen Test (BHT). This works because the only time hydrogen gets into your breath is if bacteria are fermenting carbohydrates. The test is simple. The doctor will take a reference sample of your breath.
Then you drink some lactose. They test again at intervals for several hours. The results need to go to a big lab, so there may be some places where it is not available. In those places, an alternate test, the Blood Glucose Test (BGT) is used.
This measures whether your blood sugar increases after drinking lactose, as it will if you digest it. The big disadvantage is that it is a blood test, which means collecting several blood samples. It is also not quite as reliable as the BHT. But it should be available everywhere. For more info, see my Tests for Lactose Intolerance page.
Is LI the same as Milk Allergy?
Not at all. They are not even related, although some unfortunate individuals can have both simultaneously.
As I’ve said, LI is simply an insufficient amount of lactase needed to digest the milk sugar, lactose. Allergies come from proteins.
The body’s immune systems treat proteins that leak through the intestines and into the bloodstream the same way they treat truly dangerous invaders, like bacteria. True allergies cause mainly skin (rashes, hives) and respiratory (wheezing, asthma) symptoms.
However, there is more than one immune response system in the body. Some of these create what are called hypersensitivities, and these can produce symptoms much like LI, especially in young children. For a much fuller discussion, see my Lactose Intolerance versus Milk Allergy page.
When Do Most People Stop Producing Lactase?
Lactase is the last intestinal enzyme to develop and is present in the smallest quantities. Hardly surprising then to learn that it is also the first to go. Generally speaking, those populations with the highest percentage of LI among adults will also lose their lactase at the youngest age. A few may even start losing it in their first year of life.
Many more will keep their lactase high through age five (i.e., after weaning) and only then see a drop. In others, lactase production may fall very, very gradually throughout life so that symptoms from milk will not be noticed until adulthood.
A few people have first reported lactose intolerance in their seventies. And many people simply keep producing sufficient lactase and never have LI at any time in their lives.
Who is Likely to Develop LI?
Whether you maintain a high level of lactase production or switch it off early in life is genetically controlled. Anyone whose ancestors were born in Great Britain, France, Germany or Scandinavia is very, very unlikely to be or become LI. Those whose families originated in eastern Europe, northern India or anywhere along the Mediterranean shore are about as likely as not to be LI. Except for a few isolated populations, LI is omnipresent in all the world’s other ethnic groups.
The U.S. is a milk-drinking nation with generally low levels of LI precisely because the vast majority of Americans are descended from northwestern Europeans who brought their cows and their Lactose Persistent (LP) genes with them when they settled the country.
Even so, LI is probably at its highest levels today since the time when the universally LI Native Americans were sole possessors of the continent. Changing patterns of immigration have greatly increased the number of Americans who boast ancestors from historically moderate and high LI areas of the world, such as Africa, Asia, Arabia, and southern and eastern Europe.
But anybody can develop what is called Secondary LI if their intestines have been damaged by drugs, disease, or surgery. Most people who don’t naturally have LI will soon regain their ability to drink milk, although a few have serious enough damage that they never recover.
Young children often have temporary bouts of Secondary LI because their intestines are so delicate that even a bad case of diarrhea from a “stomach flu” can know their lactase-making ability.
Will All Dairy Products Create LI Symptoms?
Yes and no. Yes, all dairy products contain lactose and so theoretically will produce LI symptoms when eaten. Realistically, though, it all depends. Butter and many aged pieces of cheese, for example, have very little lactose left in them.
Most people would have to eat enough to get sick for other reasons before they ate enough lactose to affect them. And even if you drink milk, which is probably ten times higher in lactose than butter is, whether you developed symptoms would still depend on how much milk you drink, how much lactase production you have left, whether you drank the milk with a meal or all by itself, and other variables.
Studies show that about one-fifth to one-third of people with LI develop symptoms from a whole 8-ounce glass of milk. But two glasses will cause symptoms in about 90% of those who are LI. Overindulging in any dairy product will almost assure unpleasant consequences.
Be sure to check out my Dairy Facts section. It describes every milk product in existence, gives lactose percentages, and tries to sort out some tricky issues about what is really milk-derived and what isn’t.
Can Anything be Done to Cure LI?
No. Let me say this in capital letters: LACTOSE INTOLERANCE IS NOT A DISEASE. IT IS A NATURAL CONSEQUENCE OF AGING IN MOST PEOPLE. No one has ever found a way to restart or increase lactase production once it has declined.
Can Anything be Done to Alleviate LI Symptoms?
Ah, that’s a better question. The answer is yes, but to do so you have to focus on the true problem. Antacids aren’t the answer, because they work on stomach gas rather than gas formed in the colon. Antidiarrhea medicine is not really helpful, because you want the offending lactose out of your system as soon as possible.
Antiflatulents may be of some help in controlling the worst gas pains but don’t attack any of the other symptoms. In short, by the time you start feeling the symptoms, it’s almost too late to do anything useful about them. Prevention is the key. You can reduce symptoms by reducing the amount of lactose entering your intestines by doing the following:
Eat foods whose dairy products are naturally low in lactose, like butter, margarine, or aged cheeses. Eat foods that are naturally well-tolerated even by most people with Lactose Intolerance. These foods include yogurts and other fermented milk, like kefir and kumiss.
Have smaller portions of dairy products. Have half a glass of milk at a time instead of a whole glass. Have a few sips of a cream soup rather than a whole bowl. Eat the lactose as part of a meal. For example, by having cornflakes with milk, most people will get fewer symptoms than by having the milk alone.
Or try any one of hundreds of milk substitutes. Go to my Product Clearinghouse section to get brand names in a dozen different categories.
Your other choice is to break the lactose down before it can do any damage. Since you can’t get your body to produce more lactase, a reliable outside source of it is needed. Lactase pills exist that are cheap and efficient. They most definitely work, although you may have to experiment to find the one that works best for you and the number that you must take with any given food.
You can also buy lactase drops to add to milk to pre-digest the lactase there, although you have to let the milk sit for a day in the refrigerator before you drink it. I carry pills with me everywhere I go, just in case. See my Lactase page for more information.
You can also try changing the bacteria in your colon from those that ferment lactose, producing gas, to those that digest lactose and so produce no symptoms. See two important pages: A Lactose Intolerance Cure!? and The DairyCare Controversy.
So, Really, How Serious a Problem is LI?
If you believe everything you read, LI may be the most widespread medical condition in the U.S. Estimates in print run as high as 80,000,000 people, or as many as voted for Clinton and Bush combined in the 1992 presidential election.
If you believe the doctors, these numbers are wildly overinflated. Dr. Michael Levitt, a veteran in gastrointestinal research, says that the marketers are “overdoing the severity of the problem.” Another well-known LI scholar, Dr. Douglas McGill, says, “From my perspective, lactose intolerance has been a fad for 30 years now. There is nothing new except that business is after it”.
So who should you believe? Neither side. They’re both wrong.
The truth lies somewhere in the middle. For millions of Americans LI is a real problem. Needing to think about every morsel of food you put into your mouth, needing to deal with the consequences if enough milk slips by, needing to look for special products and needing to adapt recipes and forego some favorite foods makes LI a constant trial, even with the wealth of milk alternatives and lactase products on the market.
It is easier to not have milk than to hope you’ve gauged a dose of lactase correctly or to remember to carry lactase with you at all times. Children are especially bothered by being thought of as different due to their LI. A world in which milk was easier to avoid would be preferable to one in which measures must constantly be taken to avoid feeling ill.
LI may be a problem, but it is not one of an epidemic scale. 80 million people are not descending onto their local supermarkets demanding alternatives to milk. That big market just doesn’t exist. But guesstimates from marketers who specialize in selling to the LI and extrapolation off census data suggest that we number maybe 10 million strong.
That’s a vast pool of dollars that could be swung toward restaurants who feature milk-free meals, bakeries that market milk-free bread and desserts, food giants who list amounts of lactose on their products’ nutrition labels or smaller firms who target the LI in their advertising.
Our numbers are large enough to command attention and respect if only we could make our voices heard.