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How to know if you're lactose intolerant

By Robert A. Fried, MD Jun 30, 2022 • 4 min


Lactose intolerance is a common condition that affects millions of people. Many people suspect they're lactose intolerant but don't know how to tell for sure. There are several methods that can help determine if someone is lactose intolerant.

Try eliminating lactose from your diet

If you think you're lactose intolerant, you might consider avoiding all forms of dairy for a few days, see if your symptoms go away, and then add dairy back slowly. Take notes of any symptoms that return. If you stop and start a couple of times, and your symptoms keep going away when you're off dairy and keep coming back when you start dairy again, you may be intolerant to lactose.

When conducting a stop-start trial at home, keep in mind that lactose is present in some foods that aren't dairy products. Many processed foods and meats, baked goods and even nondairy coffee creamers can have small amounts of lactose. It’s important to check food labels carefully to be sure you're eliminating all sources of lactose while doing a trial at home. Be sure to let your healthcare provider know if your symptoms got better on the days you didn't have dairy or other foods with lactose.

Are there lab tests for lactose intolerance?

It's important to speak with your healthcare provider if you think you might have lactose intolerance. If you haven't already tried eliminating lactose from your diet to see if symptoms improve, your provider might suggest it. 

Tests that your healthcare provider might order to help diagnose lactose intolerance include:

  • Hydrogen breath test. This involves drinking a liquid containing a standard amount of lactose. Over the course of a few hours, you'll be asked about your symptoms, and you'll breathe into a special container. If you're not completely digesting the lactose, the amount of hydrogen in your breath will rise and your symptoms will likely worsen. Worsening symptoms and higher-than-normal levels of hydrogen in your breath may result in a lactose intolerance diagnosis. 
  • Lactose tolerance test. This involves drinking a liquid that contains lactose, followed by a blood glucose test two hours later. Lactose is converted into glucose when it’s digested properly. If your glucose doesn't increase, you may not be digesting the lactose you get from dairy products, and this may indicate lactose intolerance. 

Lactose intolerance can be uncomfortable, and it might be embarrassing to talk with your healthcare provider about symptoms like bloating and gassiness. But if you’re experiencing symptoms, it’s important to see your provider for an evaluation and guidance on how best to address your issues, including the possibility of taking lactose intolerance supplements.

Published June 2022.