context: Millions of Americans can't digest a certain sugar in milk and milk products called lactose. If you're one of them, you have lactose intolerance. The condition isn't harmful, but it can be uncomfortable and may be embarrassing. There's no cure, but you can manage it by watching how much milk or milk products you drink or eat. Being lactose intolerant is not the same as being allergic to milk. Lactose is the sugar that's in milk. Our bodies use an enzyme called lactase to break down that sugar so we can absorb it into our bodies. But people with lactose intolerance don't have enough lactase. It's produced in the small intestine. Even with low levels of lactase, some people can digest milk products just fine. For people who are lactose intolerant, their low lactase levels gives them symptoms after they eat dairy. When we drink milk or have a milk-based product, lactase in our small intestines breaks down the milk sugar. It then gets absorbed into the body through the small intestines. But people who are lactose intolerant don't have it so easy. In them, the lactose doesn't get broken down. Instead, it goes on to the colon, where it mixes with normal bacteria and ferments. It can cause things like gas, bloating and diarrhea. There are some steps you can take to test yourself: Go without milk or milk products for a couple of weeks. If your symptoms disappear, bring dairy products back into your diet a little at a time to take note of how you react. If your symptoms continue after cutting out the dairy -- or if they return -- see your doctor to find out what's going on. Believe it or not, most adults around the world can't digest milk -- 40% of humans stop producing enough lactase to digest milk between the ages of 2 and 5. In the United States, it's estimated that just over one-third of people are lactose intolerant. It is most common among: Asian- Americans African- Americans Mexican- Americans Native Americans It can also be inherited or associated with other specific diseases. Our bodies react to milk in ways that are easily measured. Two common tests for adults are: Breath test. This will show if you have high levels of hydrogen when you exhale. If you do, you might be lactose intolerant. That's because hydrogen is given off when lactose is broken down in the colon. The hydrogen gets taken by the blood up to your lungs, and then you exhale it. Blood test. This can show how your body reacts after you drink something with a lot of lactose. However, this test is usually not done. Doctors can also take a stool sample from babies and young children. You may still be able to eat or drink small amounts of milk. Some people do better if they have their dairy with a meal. And, some dairy products, like hard cheese or yogurt, may be easier to digest. Also, there are lots of lactose-free dairy products at the supermarket. Or you can take commonly found over-the-counter supplements (like Lactaid) to break down the milk sugars if you still want the real thing. But if you give up milk completely, you can still get plenty of calcium, vitamin D and other nutrients in a healthy diet. Instead of milk, you can substitute these foods: Almonds Dried beans Tofu Collards Kale Calcium-fortified orange juice and soy milk Fatty fish, like salmon, tuna and mackerel Egg yolks Beef liver If you have symptoms of lactose intolerance, see your doctor. And if you're diagnosed with it, talk with her about how to be sure you're eating right.