Lactose Intolerance 101 — Causes, Symptoms and Treatment
Lactose intolerance is very common.
In fact, it's thought to affect around 75% of the world's population (1).
People with lactose intolerance experience digestive problems when they eat dairy, which can have a negative effect on quality of life.
Lactose intolerance is a digestive disorder caused by the inability to digest lactose, the main carbohydrate in dairy products.
It can cause various symptoms, including bloating, diarrhea and abdominal cramps.
People with lactose intolerance don't make enough of the enzyme lactase, which is needed to digest lactose.Lactose is a disaccharide, meaning that it consists of two sugars. It is made up of one molecule each of the simple sugars glucose and galactose.
The lactase enzyme is needed to break lactose down into glucose and galactose, which can then be absorbed into the bloodstream and used for energy.
Lactose is also found in breast milk, and almost everyone is born with the ability to digest it. It is very rare to see lactose intolerance in children under the age of five.
Currently, about 75% of the world's population is lactose intolerant. The risk varies greatly between countries.
Bottom Line: Lactose intolerance is the inability to digest lactose, the main carbohydrate in dairy. It is caused by reduced production of the enzyme lactase in your gut.
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 (5).
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 (1).
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 (6).
Bottom Line: Primary lactose intolerance is common and involves reduced lactase production with age. Secondary lactose intolerance is caused by inflammation in the gut, secondary to an infection or disease.
If not managed properly, lactose intolerance can cause severe digestive problems.
- Abdominal cramps
Some people also experience urgency to go to the toilet, nausea, vomiting, pain in the lower belly and occasionally 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 the bloating, flatulence and pain.
The severity of symptoms can vary, depending on how much lactose you can tolerate and how much you have eaten (9).
Bottom Line: Lactose intolerance can cause digestive problems. The main symptoms are bloating, gas, abdominal cramps and diarrhea.
Dairy is the term used to describe milk or products made from milk.
Bottom Line: Dairy is high in many nutrients, and is the world's best source of calcium. Removing dairy means you need to get these nutrients from other foods instead.
Lactose is found in dairy foods and products that contain dairy.
Dairy Foods That Contain Lactose
The following dairy products contain lactose:
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
- Breads and baked goods
- 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 solids
- Milk powder
- Whey protein
- Milk casein
- Milk sugar
- 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.
Bottom Line: Dairy products contain lactose. It's important to check the label of manufactured foods to see if they contain any hidden lactose.
All dairy foods contain lactose, but this doesn't mean they are totally off limits for people with lactose intolerance.
Most people with lactose intolerance can tolerate small amounts of lactose. For example, some people can tolerate the small amount 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, spread throughout the day (23).
In fact, research has shown that many people with lactose intolerance can tolerate up to 12 grams of lactose in one sitting, which is approximately the amount in 1 cup (230 ml) of milk (2, 23, 24, 25, 26, 27).
Some types of dairy are also naturally low in lactose when eaten in their usual portions. Butter, for example only contains 0.1 grams of lactose per 20-gram portion.
Certain types of cheese also have less than 1 gram of lactose per serving. This includes cheddar, Swiss, Colby, Monterey Jack and mozzarella.
Bottom Line: Most people with lactose intolerance can tolerate small amounts of lactose. Dairy products like butter, yogurt and some cheeses are often tolerated better than milk.
Dairy foods are excellent sources of calcium, but eating dairy isn't essential.
The recommended intake for calcium is 1,000 mg per day.
Some good non-dairy sources of calcium include:
- Calcium-fortified foods: There are many calcium-fortified foods, including juices, breads and non-dairy milks such as almond, soy or oat milk. Shake the carton before use, since the calcium can settle on the bottom.
- Boned fish: Canned fish with bones, such as sardines or whitebait, are high in calcium.
- High-calcium plants foods: Many plant foods contain reasonable amounts of calcium. However, this calcium is often poorly absorbed due to the presence of antinutrients like phytate and oxalate.
Here's a list of lactose-free foods that are high in bioavailable calcium:
- Fortified non-dairy milk: 300 mg calcium in an 8 oz (240 ml) serving
- Fortified fruit or vegetable juice: 300 mg calcium in an 8 oz (240 ml) serving
- Fortified tofu: 200 mg calcium in a 1/2 cup serving
- Cooked collard greens: 200 mg of calcium in a 1/2 cup serving
- Dried figs: 100 mg calcium in five figs
- Kale: 100 mg calcium in a 1/2 cup serving
- Broccoli: 100 mg calcium in a 1/2 cup serving
- Soybeans: 100 mg calcium in a 1/2 cup serving
- Tempeh: 75 mg calcium in a 1/2 cup serving
- Cooked bok choy or mustard greens: 75 mg calcium in a 1/2 cup serving
- Almond butter: 75 mg calcium in 2 Tablespoons
- Tahini: 75 mg calcium in 2 Tablespoons
Bottom Line: If you remove dairy from your diet, you need to replace it with suitable alternative sources of calcium.
If you don't want to give up dairy, then there are a few natural treatments that can help.
It's possible to buy enzymes to help digest lactose. These are tablets you swallow or drops you add to foods and drinks.
Nevertheless, lactase enzyme supplements may be very effective for some people.
One study examined the effects of three different types of lactase supplements in lactose-intolerant people who took 20 or 50 grams of lactose (42).
Compared to placebo, all three lactase supplements improved overall symptoms when taken with 20 grams of lactose.
However, they weren't effective at the higher dose of 50 grams of lactose.
If you are lactose intolerant, regularly including lactose in your diet could help your body adapt to it (43).
In one small study, nine lactose-intolerant people experienced a threefold increase in their lactase production after 16 days of eating lactose (47).
More rigorous trials are needed before definite recommendations can be made, but it may be possible to train your gut to tolerate lactose.
Probiotics and Prebiotics
Prebiotics are types of fiber that function as food for these bacteria. They feed the beneficial bacteria you already have in your gut, so that they thrive.
Bottom Line: There are several ways to reduce lactose intolerance, including enzyme supplements, lactose exposure and eating probiotics or prebiotics.
Removing dairy from your diet can mean you miss out on important nutrients. However, it's not always necessary to completely avoid dairy if you are lactose intolerant.
Most people with lactose intolerance can tolerate small amounts of dairy.
If you do need to remove dairy completely, it's perfectly possible to have a healthy and balanced diet without it.
Just make sure to include other sources of calcium to get everything you need.