How to Test for Lactose Intolerance

Written by: Sarah Glinski, RD

Updated: February 27th, 2026

Lactose intolerance is a digestive disorder where a person cannot digest the lactose found in dairy products due to not producing enough lactase enzyme. It’s one of Canada’s most common food intolerances, with research published in the Journal of the Canadian Association of Gastroenterology indicating that around 44% of Canadians live with lactose intolerance.

Proper testing is essential for symptom management and avoiding unnecessary dietary restrictions. Many people self-diagnose with lactose intolerance and eliminate dairy products unnecessarily, which can lead to deficiencies in nutrients like calcium and vitamin D.

Testing for lactose intolerance helps confirm whether symptoms are due to lactose intolerance or another digestive issue. Read on to learn about the different ways to test for lactose intolerance, when to consult a healthcare provider, and what to do after you receive a diagnosis of lactose intolerance.

Identifying Lactose Intolerance

Lactose intolerance occurs when a person cannot fully digest lactose, the sugar naturally found in animal milk and dairy products. This is due to a deficiency in their body’s production of the enzyme lactase.

Lactase breaks lactose down into two simple sugars, glucose and galactose, that can be more easily absorbed. If lactase is lacking, lactose does not get properly broken down and enters the large intestine intact, where it draws water into the bowel and gets fermented by gut bacteria. This can cause uncomfortable digestive symptoms in susceptible individuals.

Common symptoms of lactose intolerance include:

Excessive gas
Bloating
Abdominal pain
Abdominal cramping
Diarrhea
Nausea
Vomiting

Symptoms can start as soon as 30 minutes after eating dairy, but can also be delayed up to two hours after dairy consumption.

It’s important to note that lactose intolerance is different than a milk allergy. Lactose intolerance is a digestive issue, whereas a milk allergy involves an immune response to the proteins found in dairy products. A milk allergy can cause hives, swelling, difficulty breathing, or even anaphylaxis, while lactose intolerance leads to gastrointestinal symptoms.

If a person has a milk allergy, they must avoid all dairy products to prevent an immune response from occurring. In contrast, lactose intolerance exists on a spectrum, with many lactose intolerant people able to tolerate small amounts of lactose. This is because people with lactose intolerance produce varying amounts of the lactase enzyme. The more enzyme produced, the more lactose a person can tolerate.

Testing for Lactose Intolerance

There are two main lactose tolerance tests: the hydrogen breath test and the glucose blood test.

Hydrogen breath test

A hydrogen breath test is the most common test for lactose intolerance. For this test, you’ll drink a liquid containing lactose. Then, you’ll breathe into a balloon-like container every 30 minutes for a few hours to measure the amount of hydrogen gas in your breath.

Measuring the hydrogen in your breath helps assess whether you’re lactose intolerant because if you can’t digest the lactose from the drink, it gets broken down by the bacteria in your colon, creating hydrogen gas. If you experience worsening symptoms and have an increased level of hydrogen in your breath after the test, you likely have lactose intolerance.

Glucose blood test

A glucose blood test can also be used to test for lactose intolerance. In this test, you’ll also drink a liquid containing lactose. Your test provider will measure the glucose in your blood before and after drinking the liquid.

Measuring the amount of glucose in your blood helps assess whether you’re lactose intolerant because if your body cannot digest lactose, it will not get broken down into glucose and galactose, and your blood levels of glucose won’t rise.

If your blood glucose levels don’t rise, you likely have lactose intolerance. However, if you have diabetes, your blood glucose may rise even if you have lactose intolerance. In this case, you may need to undergo more testing to determine the cause of your symptoms.

Options for People Without a Family Doctor

If you cannot access testing for lactose intolerance, you can try switching to lactose-free dairy for a short time to assess your lactose tolerance. This involves removing high-lactose foods from your diet for a few weeks and replacing them with lactose-free versions, then gradually reintroducing high-lactose foods to see if symptoms return. If symptoms return when you reintroduce high-lactose foods like milk and some types of yogurt, you likely have lactose intolerance.

Other options for guidance if you suspect you have lactose intolerance include:

Visiting a walk-in clinic or pharmacist for initial advice on managing symptoms.
Speaking with a registered dietitian for personalized dietary advice to manage lactose intolerance without unnecessary food restrictions.

Remember, just because you have lactose intolerance doesn’t mean you have to eliminate dairy altogether. Some dairy products, like hard or aged cheeses and Greek yogurt, contain relatively low amounts of lactose and may be tolerated even if you have lactose intolerance.

What to Do After Diagnosis

Once you’ve been diagnosed with lactose intolerance, there are many ways to manage symptoms while maintaining a balanced diet.

Here are some strategies for managing lactose intolerance:

Choose lactose-free dairy products like lactose-free milk, yogurt, and cheese, which provide the same nutrients as lactose-containing dairy but without the discomfort.
Choose lower-lactose dairy products, like aged cheeses and Greek yogurt.
Use over-the-counter lactase enzyme supplements to help break down the lactose in dairy products, allowing you to enjoy dairy with fewer symptoms.
If you’re reducing your dairy intake, you may need a calcium supplement to ensure you meet your calcium needs. You may also need a vitamin D supplement, especially in the winter months. It’s best to discuss this with your doctor, dietitian, or pharmacist.

Final Thoughts

Testing for lactose intolerance helps confirm a diagnosis to prevent unnecessary food restrictions. You may tolerate the small amounts of lactose found in aged cheeses and Greek yogurt even if you have lactose intolerance. Alternatively, you can choose lactose-free dairy products or use lactase drops or tablets when eating lactose-containing foods.

If you suspect you may have lactose intolerance, it’s important to seek guidance from a healthcare provider. They can help you manage your symptoms while ensuring you get enough essential nutrients like calcium and vitamin D. Remember, with the right approach, you can enjoy dairy without discomfort!

References

Fung, M., Xue, X., & Szilagyi, A. (2020). Estimating Lactase Nonpersistence Distributions in the Multi-Ethnic Canadian Demographic: A Population-Based Study. Journal of the Canadian Association of Gastroenterology, 3(3), 103-110. https://doi.org/10.1093/jcag/gwy068
Canadian Digestive Health Foundation (n.d.). Lactose Intolerance. Retrieved February 3, 2025, from https://cdhf.ca/en/digestive-conditions/lactose-intolerance/
Government of Canada (2016, August 31). Milk – A priority food allergen. Retrieved February 3, 2025, from https://www.canada.ca/en/health-canada/services/food-nutrition/reports-publications/food-safety/milk-priority-food-allergen.html
Canadian Digestive Health Foundation (2024, February 29). Understanding Lactose Intolerance and Lactose-Free Alternatives. Retrieved February 3, 2025, from https://cdhf.ca/en/understanding-lactose-intolerance-and-lactose-free-alternatives/
NIH (n.d.). Lactose Tolerance Tests. MedlinePlus. Retrieved February 3, 2025, from https://medlineplus.gov/lab-tests/lactose-tolerance-tests/