Lactose Intolerance and Food Intolerances

What lactose intolerance is

Lactose intolerance is a condition in which you have digestive symptoms after you consume foods or drinks that contain lactose, the natural sugar in milk and milk products. [1] Symptoms can begin within a few hours and include bloating, diarrhea, gas, nausea, belly pain, rumbling sounds and sometimes vomiting. They may be mild or severe depending on how much lactose you have. [2]

The cause is lactose malabsorption: the small intestine makes low levels of lactase, the enzyme that breaks down lactose. Undigested lactose passes into the colon, where bacteria break it down and create fluid and gas. [2] Experts estimate that about 68 percent of the world's population has lactose malabsorption, and about 36 percent of people in the US. But not everyone with lactose malabsorption has lactose intolerance. [1]

Lactose intolerance can also be secondary to an injury of the small intestine from diseases such as Crohn's disease or celiac disease. If the cause is treated, you may be able to tolerate lactose again. [2]

Lactose intolerance is not a milk allergy

They have different causes. Lactose intolerance is a problem digesting milk sugar. A milk allergy is an immune response to proteins in milk, usually appears in the first year of life, and a serious allergic reaction to milk can be life threatening. [2] If you think you may have a food allergy, talk with a clinician.

Other conditions can look the same

IBS, celiac disease, inflammatory bowel disease and small bowel bacterial overgrowth can cause symptoms similar to lactose intolerance. [3] See irritable bowel syndrome, celiac disease and inflammatory bowel disease. That is why guessing and cutting out many foods is not a reliable way to find the cause.

How it is tested

A doctor asks about your symptoms, history and eating habits, and may ask you to stop milk and milk products for a period of time to see if symptoms go away. If they don't, more tests may follow. [3] A hydrogen breath test is used to diagnose lactose malabsorption and intolerance: you drink a measured amount of lactose and breathe into a container over several hours while symptoms are tracked. [3]

Managing it without giving up all dairy

Most people with lactose intolerance can have some lactose without symptoms. Research suggests many could have 12 grams of lactose, about the amount in 1 cup of milk, with no or only mild symptoms. [4]

The Functional Foods yogurt page summarizes the research on yogurt and lactose tolerance.

Calcium and vitamin D

If you avoid all milk and milk products you may get less calcium and vitamin D than you need. [4] Calcium also comes from fish with soft bones such as canned salmon or sardines, broccoli and leafy greens, almonds and tofu. Talk with your doctor or dietitian about whether you are getting the nutrients you need, and before using dietary supplements. [4] See osteoporosis and bone health for bone health overall.

Food intolerances more broadly

Special diets are used when a specific cause is found: a gluten-free diet for celiac disease, less lactose for lactose intolerance, less fructose (especially high-fructose corn syrup) for dietary fructose intolerance, and a short low-FODMAP trial for IBS. [5] If you suspect triggers, your doctor may ask you to keep a food and symptom diary and may refer you to a registered dietitian to create a healthy eating plan. [5]

Be cautious about food-sensitivity tests sold directly to consumers; see the claim check on gut and food-sensitivity tests. For a structured approach to carbohydrate triggers in IBS, see the low-FODMAP diet.

When to get help

See a clinician if symptoms persist, if you are not sure of the cause, or if you have blood in the stool, weight loss, or severe pain. [6] Check any supplement or lactase product with a pharmacist and read how interactions work. See digestive symptoms: red flags.