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Lactose intolerance is caused by a deficiency in lactase — the enzyme that breaks down the sugar in milk, called lactose. Common symptoms include bloating, abdominal cramps, nausea, and diarrhea.

If you’ve ever felt a foreboding rumbling in your stomach shortly after eating, you may have wondered whether you’re lactose intolerant.

Lactose is a type of sugar found in milk products. Some people are unable to digest it properly, leading to unpleasant digestive symptoms after dairy intake.

This article reviews what lactose intolerance is, along with how it’s diagnosed and treated.

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What is lactose intolerance?

Lactose intolerance is a digestive disorder caused by the inability to digest lactose, the main carbohydrate in dairy products. It’s very common, affecting around two-thirds of the world’s adult population at minimum (1).

This condition occurs if your body doesn’t make enough of the enzyme lactase, which you need to digest lactose (1).

People with lactose intolerance experience digestive problems when they consume dairy, which can negatively affect their quality of life.

These symptoms include bloating, diarrhea, and abdominal cramps.

Can you develop lactose intolerance over time?

Lactose is found in breast milk, and almost everyone is born with the ability to digest it. However, you can develop lactose intolerance at any age, even well into adulthood (1).

Several types of lactose intolerance exist, and they may be caused by different factors. However, all lactose intolerance is characterized by a deficiency in the enzyme lactase.

Summary

Lactose intolerance is the inability to digest lactose, the main carb in dairy. It’s caused by reduced production of the enzyme lactase in your gut.

Symptoms of lactose intolerance

If not managed properly, lactose intolerance may cause severe digestive problems. These symptoms may appear as quickly as 30–60 minutes after eating.

The most common symptoms are (1):

• bloating
• abdominal cramps
• gas
• diarrhea
• nausea

Some people also experience an urgent need to go to the toilet, vomiting, lower belly pain, and constipation.

Diarrhea occurs due to undigested lactose in your small intestine, which causes water to move into your digestive tract (2).

Once it reaches your colon, the lactose is fermented by the bacteria in your gut, forming short-chain fatty acids (SCFAs) and gas. This causes bloating, gas, and pain (2).

The severity of symptoms varies based on how much lactose you can tolerate and how much you’ve eaten.

Fortunately, these symptoms last only briefly. You’re also typically not affected unless you consume large amounts of lactose or have another condition that’s worsened by the digestive irritation caused by lactose intolerance.

summary

Lactose intolerance may cause digestive problems, including bloating, gas, abdominal cramps, and diarrhea.

Causes and types of lactose intolerance

Lactose is made up of the simple sugars glucose and galactose.

You need the enzyme lactase to break lactose down into glucose and galactose, which your body then absorbs into your bloodstream for energy.

Without sufficient lactase, lactose moves through your gut undigested and causes digestive symptoms. Still, there are multiple causes of lactase deficiency (1).

Here are the different types of lactose intolerance.

Primary lactose intolerance

Primary lactose intolerance — the most common type — is caused by a decrease in lactase production with age. As such, you lose the ability to absorb lactose over time (1, 3).

This form of lactose intolerance may be partially genetic since it’s more common in some populations than others.

Studies estimate that this condition affects under 10% of Northern European people, around 50% of Latin and Middle Eastern people, and 80–99% of African and Asian people (1).

Secondary lactose intolerance

Secondary lactose intolerance develops as a result of another condition that affects the small intestine, where lactase is produced. This is because inflammation in the wall of your gut may lead to a temporary decline in lactase production (1, 4).

Possible causes of secondary lactose intolerance include Crohn’s disease, celiac disease, chemotherapy, ulcerative colitis, and aging (1).

Congenital lactose intolerance

Congenital lactose intolerance is present in newborns. It’s a rare, inherited type of this condition, and both parents must possess the particular gene mutation for congenital lactose intolerance for the infant to be born with it (1, 5).

These infants are unable to nurse due to the lactose content of breast milk, and this condition may even be fatal if not caught quickly. Side effects may include severe diarrhea and high calcium levels (1, 2).

This condition is also lifelong (1, 2).

Developmental lactose intolerance

Developmental lactose intolerance occurs in infants, too. It’s typically only seen in premature babies, who are born before their digestive system is fully developed, and it causes symptoms like digestive distress (2, 5).

This condition typically resolves on its own as the baby grows, but in the meantime, your infant may need lactose-free formula rather than breast milk (5).

Risk factors

Some people may have an increased risk of lactose intolerance. Risk factors to look out for include having the following (1):

• Asian or African heritage
• a medical history of digestive problems or disease
• relatives who are lactose intolerant

summary

Lactose intolerance is typically categorized as primary, which is caused by declining lactase levels as you age, or secondary, which is caused by another condition that affects your small intestine. In rare instances, this condition can also affect babies.

Tests for lactose intolerance

Here are the ways that your doctor can test you for lactose intolerance (1):

• Hydrogen breath test. This test measures hydrogen in your breath after lactose intake. High amounts of hydrogen suggest digestive problems that may be related to lactose intolerance but also caused by other issues.
• Lactose tolerance test. This test measures your blood sugar after lactose ingestion. If you have lactose intolerance, your blood sugar levels won’t be affected because your body can’t break down lactose.
• Genetic test. This test checks for genetic causes of lactose intolerance, but people with secondary lactose intolerance may receive a false negative.
• Lactase activity at jejunal brush border. This invasive and expensive method requires a biopsy of the jejunal brush border, which is part of your small intestine, but is a definitive way to assess lactase activity.
• Stool acidity test. Often used for babies and infants, this test measures stool acid levels, which have a lower pH in cases of lactose intolerance (6).

You can also do an elimination test by yourself if you think you have lactose intolerance. To do it, eliminate lactose from your diet for at least 2 weeks, then reintroduce dairy to see whether you experience any digestive symptoms.

While an elimination test may help you understand whether you have trouble digesting lactose, seeking an official diagnosis from a healthcare professional may help you avoid unnecessarily eliminating dairy from your diet if your symptoms are caused by another condition.

summary

Your doctor may choose among several tests to check for lactose intolerance. Otherwise, you can try an elimination test yourself.

How to get dairy’s nutrients without consuming dairy

Dairy products, which include milk and all products made from milk, are highly nutritious.

In fact, dairy intake is linked to higher bone mineral density, which may help reduce your risk of bone fractures as you age (7, 8).

However, people with lactose intolerance may need to reduce or eliminate their dairy intake, potentially depriving them of key nutrients like calcium.

Dairy foods are excellent sources of calcium, but eating dairy isn’t critical for your health. You can follow a very healthy diet without dairy — as long as you eat other foods that are high in calcium.

Some good nondairy sources of calcium include:

• Calcium-fortified foods. Calcium-fortified foods include juices, breads, and nondairy milks like almond, soy, and oat milk. Just 1 cup (240 mL) of calcium-fortified orange juice provides 27% of the Daily Value (DV) for this mineral (9).
• Boned fish. Canned fish with bones, such as sardines, salmon, or whitebait, are high in calcium. A mere 3 ounces (85 grams) of canned salmon with bones provides 14% of the DV (9).
• High calcium plant foods. Many plant foods, such as kale and broccoli, contain reasonable amounts of calcium. Just 1/2 cup (113 grams) of boiled spinach provides 9% of the DV for calcium (9).

For calcium-fortified juices and nondairy milks, be sure to shake the carton before use, as the calcium can settle on the bottom.

Furthermore, keep in mind that calcium from plant foods is often poorly absorbed due to the presence of antinutrients like phytate and oxalate (9).

summary

There are many ways to get enough calcium without consuming dairy. Calcium-fortified foods, canned fish with bones, and dark leafy greens all provide calcium.

Which foods contain lactose?

Lactose is found in almost all dairy products, as well as foods that contain dairy.

Dairy foods

The following dairy products contain lactose (10):

• cow’s milk (all types)
• goat’s milk
• cheese (including hard and soft cheeses)
• ice cream
• yogurt
• cream
• half-and-half
• butter

Some of the foods above contain more lactose than others. For example, the lactose content of cheese varies significantly depending on the type. Soft cheeses like brie tend to be high in lactose, while hard cheeses like Parmesan contain only small quantities (11).

Foods that sometimes contain lactose

Foods that include some form of dairy as an ingredient may also contain lactose, including:

• dishes made with a creamy sauce, such as pasta alfredo
• biscuits and cookies
• chocolate and packaged treats like boiled sweets and candies
• breads and baked goods
• cakes
• breakfast cereals
• instant soups and sauces
• processed meats, such as presliced ham and sausages
• ready-made meals
• pasta sauces and gravies
• potato chips, nuts, and flavored tortillas
• desserts and custards

As such, it’s best to carefully check the ingredient list of any packaged food if you have lactose intolerance.

Other names for added dairy

You can check whether a product contains dairy by reading the ingredient list. Added milk or dairy products may be labeled 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

Lactose-free alternatives

Lactose-free alternatives exist for most foods that contain lactose.

Some dairy products can be made lactose-free by removing the lactose, which is usually broken down during manufacturing into glucose and galactose (11, 12).

On their own, these simple sugars are naturally sweeter than lactose, giving lactose-free milks a slightly sweeter taste than conventional versions (12).

Most lactose-free dairy products are prominently labeled “lactose-free.” Lactaid is just one well-regarded brand.

Plant-based dairy products — such as almond milk, coconut yogurt, soy ice cream, and cashew cheese — are also naturally lactose-free.

summary

All conventional dairy products contain some amount of lactose. If you’re lactose intolerant, it’s also important to check the label of manufactured foods.

Treatment options for lactose intolerance

If you don’t want to give up dairy, a few natural treatments may alleviate lactose intolerance.

Enzyme supplements

Enzyme supplements may help your body digest lactose.

However, the effectiveness of these products may vary widely, from no discernible effect to reduced lactose intolerance symptoms with more favorable hydrogen breath test results (2, 10).

Others may experience reduced symptoms with no change in their hydrogen breath test results, suggesting a placebo effect (2, 10).

As such, it may be best to consult a doctor before trying these supplements.

Lactose exposure

If you are lactose intolerant, regularly consuming lactose may help your body adapt to it (13).

So far, studies on this strategy are limited, but initial results show positive signs.

Through regular lactose exposure, your gut microbiota may be able to produce enough lactase on its own to ease lactose intolerance symptoms — despite your body itself having a lactase deficiency (14).

Consistency is key with this method, and high fat milk like whole milk may be the best choice because your body digests it more slowly, potentially giving your gut bacteria more time to digest the lactose (2, 14).

Still, further research is necessary.

Probiotics and prebiotics

Probiotics are microorganisms that provide health benefits, while prebiotics are types of fiber that function as food for these microorganisms, feeding the beneficial bacteria in your gut.

Both probiotics and prebiotics have been shown to reduce symptoms of lactose intolerance, although most studies are small (2, 15).

Some types of probiotics and prebiotics may be more effective than others. The most beneficial probiotics are thought to be Bifidobacteria and Lactobacillus strains, which are often found in probiotic yogurts and supplements (2).

summary

You can try several tactics to alleviate lactose intolerance, including enzyme supplements, lactose exposure, and probiotic supplements. Yet, more research is needed on each of these strategies.

Can you still eat dairy with lactose intolerance?

All dairy foods contain lactose, but this doesn’t mean that they’re completely off-limits if you have lactose intolerance.

Most people with this condition can tolerate small amounts of lactose. For example, some people can stomach a splash of milk in tea but not the amount you would get from a bowl of cereal.

It’s thought that people with lactose intolerance can tolerate up to 18 grams of lactose throughout the day. In fact, research reveals that many people can tolerate up to 12 grams in one sitting, which is approximately the amount in 1 cup (240 mL) of milk (2, 16).

Some dairy products are also naturally low in lactose when eaten in their usual portions. For instance, butter only contains trace amounts of lactose (11).

Certain cheeses like Parmesan, cheddar, and Swiss likewise have less than 1 gram of lactose per 1-ounce (28-gram) serving. Generally, firm cheeses are lower in lactose than soft cheeses (11, 17, 18, 19).

Interestingly, yogurt tends to cause fewer symptoms than other types of dairy in people with lactose intolerance. This may be because the probiotics — or beneficial bacteria — in yogurt possess the lactase enzyme, helping your body break down lactose (20, 21).

summary

Most people with lactose intolerance can tolerate small amounts of lactose. Your body may digest dairy products like butter, yogurt, and hard cheeses more easily than milk.

The bottom line

Lactose intolerance is a set of symptoms caused by a deficiency in lactase — the enzyme that breaks down the milk sugar called lactose. If you have this condition, symptoms occur after you consume lactose, which is found in dairy products like milk, yogurt, and cheese.

These symptoms, which may arise shortly after eating, include abdominal pain and diarrhea.

Many people are lactose intolerant, and there are many ways to easily adjust your diet to avoid or limit lactose. These strategies include buying lactose-free foods.

If you’re concerned that you can’t tolerate dairy, rest assured that there are numerous foods and beverages you can have, along with a number of treatment options to help prevent or alleviate symptoms.

Just one thing

Try this today: Interested in lactose-free, plant-based drinks to replace milk in your diet? Here are the 9 best nondairy substitutes for milk.