What Is Lactose Intolerance? Symptoms, Causes, Diagnosis, Treatment, and Prevention

When you were a kid, your mother may have always reminded you to drink your milk. But these days many adults find themselves experiencing some degree of what’s known as lactose intolerance.

Lactose is a sugar found in dairy products. When you consume food or drink containing lactose, an enzyme in the small intestine called lactase helps you digest the sugar. But when you’re lactose intolerant, you have a decreased ability to digest these sugars, and this could create excess gas and other gastrointestinal symptoms.

The most common type of lactose intolerance is primary lactose intolerance. In primary lactose intolerance, you’re born with a normal amount of lactase. But by the time you reach adolescence or adulthood, your lactase production decreases sharply, and it could become difficult to digest foods that contain dairy. (You may hear this described as lactose nonpersistence.)

Secondary or acquired lactase deficiency arises when an infection or disease — such as celiac disease, gastroenteritis, or Crohn’s disease — damages the small intestine.

Congenital lactase deficiency is a rare inherited disorder that involves the small intestine producing little to no lactase from birth. (More on that below.)

Here’s everything you need to know about lactose intolerance — and what to do about it.

One clue that you may have lactose intolerance is that about a half hour to two hours after consuming dairy, you experience some of the following gastrointestinal issues:

• Abdominal cramping
• Bloating
• Diarrhea and loose stools
• Gas
• Nausea
• Rumbling or growling sounds
• Abdominal pain

One thing to keep in mind: Lactose intolerance is not the same as a milk allergy, which occurs when your immune system overreacts to the proteins in milk. Rather than come on gradually, the symptoms of a milk allergy — hives, wheezing, and vomiting — typically occur immediately after you ingest dairy. And milk allergy, which usually affects infants and children, can be life-threatening.

Many people with lactose intolerance have a deficiency of the enzyme lactase because their small intestine doesn’t produce enough lactase. (The medical term for this state is hypolactasia.)

This deficiency may lead to lactose malabsorption, in which undigested lactose makes its way into the large intestine and colon. There, bacteria break it down, resulting in increased gas and fluid in the colon (and unpleasant bloating, flatulence, and other tummy symptoms).

Risk factors for lactose intolerance include:

• Age (it tends to appear after adolescence or young adulthood)
• A person’s race or ethnicity
• Premature birth

If you notice that you often have gastrointestinal symptoms after eating dairy, you may want to see your doctor, who will likely ask about what you’re experiencing, your medical history, and your eating habits, and will do a physical exam or order tests to diagnose the problem.

You may also want to keep track of how much dairy you eat. (Don’t forget to note when you have these foods, and what you eat them with.) Be sure to let your doctor know which dairy foods, and how much of them, cause discomfort.

Another option is a lactose tolerance test, which measures the amount of glucose in your bloodstream after you drink a liquid that contains lactose. If your glucose level doesn’t rise, it means your body isn’t properly digesting and absorbing the lactose-filled drink. However, due to certain conditions, these tests can be inaccurate.

There’s no cure for lactose intolerance, but most people are able to control their symptoms by making changes to their diet.

There is no cure for lactose intolerance, but it is possible to manage symptoms by paying attention to — and changing — your diet. You probably do not even need to cut out dairy completely.

Start by trying different dairy products and gauging your symptoms, sticking with small amounts to see how your body responds. It may also help to not eat dairy products on their own, but to try them with other foods (milk with cereal, for example, or cheese with crackers). Certain dairy products, like hard cheeses and live-culture yogurt, are lower in lactose than others, so start with those.

RELATED: What Is an Elimination or Exclusion Diet?

You may also want to try lactose-free and lactose-reduced milk and milk products, or to ask your doctor if it makes sense for you to take a lactase tablet when you eat or drink dairy. Lactase tablets contain lactase, the enzyme that breaks down lactose. You can take them before you eat or drink milk products. You can also add lactase drops to milk before you drink it. The lactase breaks down the lactose in foods and drinks, lowering your chances of having lactose intolerance symptoms.

You should also be mindful of getting enough calcium. Ask your doctor whether it makes sense for you to take calcium supplements. And it’s especially important for kids with lactose intolerance to see a doctor, since they need calcium for growth and strong bones.

• Canned salmon or sardines
• Leafy green veggies like broccoli and kale
• Oranges
• Almonds
• Dried beans
• Tofu

Prevention of Lactose Intolerance

While there are no good ways to prevent lactose intolerance, there are ways to prevent its symptoms, as this article describes.

• Gastroenteritis (inflammation of the intestinal lining caused by a virus, bacteria, or parasite)
• Celiac disease
• Crohn’s disease
• Ulcerative colitis (ulcers in the intestinal lining)
• Irritable bowel syndrome (IBS)
• Any injury to the small bowel
• Chemotherapy or radiation treatment for cancer

A condition called small intestine bacterial overgrowth (SIBO) may also cause sensitivity to lactose — and, in some cases, the tell-tale gastrointestinal symptoms. In SIBO, slower-than-usual intestinal movements can lead to an overgrowth of bacteria in the bowels.

The Academy of Nutrition and Dietetics’s Eat Right website offers a wealth of clear and helpful information on how and what to eat when you’re lactose intolerant.

Additional reporting by Joseph Bennington-Castro.