Lactose Intolerance Test for IBS

Reviewed by: HU Medical Review Board | Last reviewed: May 2023

Many people with irritable bowel syndrome (IBS) notice that their symptoms get worse after they eat certain foods. One common food sensitivity among people with IBS is called lactose intolerance. This is when the body has a hard time digesting dairy products. For this reason, your doctor may recommend a lactose intolerance test to help diagnose IBS.1,2

Research shows that many people with IBS have a sensitivity (intolerance) to dairy. But having IBS does not automatically mean you are lactose intolerant. And being lactose intolerant does not mean you have IBS. They are 2 different digestive disorders that sometimes overlap.1

What is lactose intolerance?

Lactose intolerance is when the body has difficulty digesting lactose found in dairy products. Lactose is the sugar found in milk, cheese, ice cream, and other dairy products.3

Lactase is the enzyme produced by the intestines to digest lactose. If your body does not produce enough lactase, it is hard to break down dairy. This can lead to unpleasant digestive symptoms.3

What are the symptoms of lactose intolerance?

Digestive symptoms caused by lactose intolerance usually happen 30 minutes to 2 hours after eating or drinking dairy. The symptoms may be more severe when a larger amount of dairy is consumed.3

Several symptoms of lactose intolerance are similar to IBS symptoms, such as:3

  • Diarrhea
  • Nausea
  • Abdominal cramps
  • Bloating
  • Flatulence, or gas

How is the lactose intolerance test performed?

A lactose intolerance test measures the body’s reaction to lactose. The most common lactose intolerance test is the hydrogen breath test.2,3

To perform the hydrogen breath test, you first breathe into a device called a breathalyzer, which looks like an inflatable bag. This device measures the level of hydrogen in your breath. Next, you drink a liquid containing lactose. After 30 minutes, you breathe into the breathalyzer again. Your hydrogen levels are measured once more. This process repeats every 30 minutes for about 3 to 4 hours.2,3

To prepare for this test, you will need to follow certain instructions in the days and weeks leading up to the test. You will likely be asked to do the following:2,3

  • Stop taking any antibiotics and probiotics about 1 month before the test. These medicines can disrupt your normal gut bacteria.
  • Stop taking any laxatives, fiber supplements, and antacids 1 week before the test.
  • Stop smoking 1 week before the test.
  • Not eat or drink anything 8 to 12 hours before the test.

How does the hydrogen breath test work?

When you are unable to break down certain foods – like dairy – it can lead to excess hydrogen gas in your colon. When you have excess gas, the hydrogen passes into your bloodstream, which then passes into your lungs. You then exhale the hydrogen out with your breath. That is how analyzing your breath can tell if you are lactose intolerant.2

What do the test results mean?

Normal hydrogen levels are less than 16 parts per million (ppm). If your test result is more than 16 ppm, it could mean that you were unable to digest the sugary drink and therefore have lactose intolerance.2

Sometimes further testing is needed to get definitive results. In order to get the most accurate test results, ask your healthcare team how you can best prepare for the test. Note that lactose intolerance is not the same thing as having an allergy to dairy.1-3

Are there any side effects of the test?

The hydrogen breath test is noninvasive and safe. But if you are indeed lactose intolerant, you may experience some cramping, bloating, and other digestive symptoms after drinking the lactose-containing liquid.2,3

While the test is unpleasant, the goal is to provide you with answers about why you have digestive issues in the first place. The more you know, the better you can manage your symptoms moving forward.2,3

How is lactose intolerance treated?

You can treat lactose intolerance by limiting or removing dairy products from your diet. Symptoms usually go away once all dairy products made by mammals – milk, cheese, sour cream, ice cream, etc. – are eliminated from the diet. Since many people with IBS are also sensitive to dairy, this could help reduce the frequency of IBS symptoms as well.2-5

Consider swapping out dairy products for dairy substitutes. Instead of cow’s milk, try almond, oat, or soy milk. Instead of dairy cheese, try cashew cheese. Also, be sure to read food labels carefully. Many packaged products contain milk or lactose as an ingredient.5

Some people may find they can have small amounts of milk and other dairy products without having symptoms. There are also some milk products, such as goat’s milk, fermented milk products (yogurt), and aged cheeses, that may be easier to digest. A lactase enzyme supplement taken with food may also help some people digest dairy and avoid lactose intolerance symptoms.5

Other tests for IBS

While lactose intolerance is different from IBS, the 2 often overlap. The lactose intolerance test is 1 of several tests that may be used to help diagnose IBS.1,6

Diagnostic tests for IBS are generally used to rule out other health conditions. Other tests for IBS include:6

  • Physical exam
  • Blood tests
  • Stool tests
  • Imaging tests such as a lower GI series (X-ray) or computed tomography (CT) scan
  • Colonoscopy

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