The official way of finding out

While I've talked about other ways to find out if you're lactose intolerant, there are two other more official ways. The most common way, which I've talked about is mainly to stop eating/drinking lactose products for two weeks to see if your symptoms disappear, then reintroduce it and see how you feel, is the easiest and most widely recommended. If you still have doubt in your mind, there are tests that can be done.

Both of these are performed in a doctor's office. First they will take a complete medical examination and find out your family history. Then they will most likely perform a hydrogen breath test. With this test they will test the level of hydrogen in your breath before you have anything with lactose in it. You will have to breath into a tube, which registers the hydrogen amount. Once you have some lactose, they will test the level of hydrogen every half hour for two hours. If the hydrogen levels increases over time, you are lactose intolerance. This test works because undigested lactose will sit and ferment in the intestines, creating different gases, one which is hydrogen.

The second test a doctor can perform is a endoscopy. They will send a camera and light down your stomach into your intestines. There they will take tissue samples and pictures of the inside of your intestines. By doing this they can look for clues as to why you've been having trouble with what you've been eating. They can also measure the level of lactose in the tissue sample.

For obvious reasons, like the time and discomfort, I highly recommend trying to figure out if you are lactose intolerant by changing your diet for two weeks. Keep a detailed record of what you eat everyday and how you feel. By looking at the similarities over time you can determine if you are lactose intolerant.