How to know if you're lactose intolerant

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.

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. This is called an elimination diet. It’s helpful to keep a journal of what you’ve eaten and any symptoms you experienced afterwards. 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 identify all potential sources of lactose that may be present in foods. Be sure to let your healthcare provider know about your symptoms, as you may have a different health condition. Your provider will likely perform additional testing to reach a diagnosis.

It's important to speak with your healthcare provider if you think you might have lactose intolerance or if you’re experiencing gastrointestinal symptoms often. 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 fasting for 8-12 hours and drinking a liquid that contains lactose. Blood glucose lab tests will taken at timed increments, usually one at 30 minutes, at one hour, and at two hours after drinking the liquid. 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.

Updated by Julie McDaniel, MSN, RN, CRNI, August 2024.