Lactose intolerance is the inability to digest lactose, the sugar primarily found in milk and dairy products. It is caused by a shortage of lactase in the body, an enzyme produced by the small intestine that is needed to digest lactose. While lactose intolerance is not dangerous, its symptoms can be distressing.
Symptoms of lactose intolerance occur when there is not enough lactase being produced by the body to digest the lactose consumed. Symptoms of lactose intolerance include nausea, cramps, gas, bloating, or diarrhea within 30 minutes to 2 hours after consuming milk or dairy products. The severity of symptoms varies, depending on the amount of lactose an individual person can tolerate. Some people may be sensitive to extremely small amounts of lactose-containing foods while others can eat larger amounts before they notice symptoms. Age and digestion rate may influence how much lactose an individual may tolerate.
Some causes of lactose intolerance are known. Certain digestive diseases, such as Crohn’s disease, ulcerative colitis, celiac sprue (an inherited disorder affecting the lining of the small intestine), other inflammatory bowel diseases, and injuries to the small intestine (surgery or trauma) may reduce the amount of lactase available to process lactose properly. If the small intestine is injured, lactose intolerance may be temporary, with symptoms improving after the intestine has healed.
For most people, lactose intolerance develops over time as the body produces less lactase. Certain populations are more affected than others with some degree of lactose intolerance, including Mediterraneans, Arabs, 80% of African-Americans, Mexicans, Native Americans and 90% of Asians.
The most common test for the diagnosis of lactase deficiency is the hydrogen breath test. This test is done at an outpatient clinic or doctor’s office. In practice, many doctors will ask patients who suspect they have lactose intolerance to avoid milk and dairy products for one or two weeks to see if their symptoms subside, and will then confirm the diagnosis with the hydrogen breath test.
The hydrogen breath test measures the amount of hydrogen in the breath after drinking a lactose-loaded beverage. Undigested lactose in the colon is fermented by bacteria and produces hydrogen and other gases. Hydrogen is absorbed, carried by the blood to the lungs, and exhaled. Raised levels of hydrogen in the breath within 90 minutes indicate improper digestion of lactose. This test has a 90% sensitivity to determine lactose intolerance. Certain foods, medications, and cigarettes can affect the test result, so the patient will be instructed to avoid these prior to taking the test.
The most common high-lactose foods include:
Other foods that MAY contain lactose in smaller quantities include:
When buying food, read the ingredients on food labels carefully. Ingredients derived from milk that contain lactose include:
Depending on the severity of your symptoms, you may need to avoid or limit foods containing these ingredients. Also avoid items that state “may contain milk” on the food label.
Lactose is also present in about 20% of prescription medications, such as birth control pills (oral contraceptives), and about 6 percent of over-the-counter medications, such as some tablets for stomach acid and gas. Viactiv® calcium chews contain lactose and should be avoided while following a lactose-free diet.
These medications usually affect only people with severe lactose intolerance. Ask your healthcare provider which medications contain lactose, and read the labels on over-the-counter medications to check their lactose content.
Lactose intolerance is easily treated. The goal of treatment is to control symptoms through dietary changes.
People with lactose intolerance can usually find a level of lactose-containing foods that will not produce symptoms. You can learn through trial and error what amount and type of lactose-containing products you can tolerate.
In addition, you may try consuming small amounts of milk or dairy products with meals because lactose may be better tolerated when eaten with other foods. You may be better able to tolerate certain dairy products that contain lower amounts of lactose, including cheese and cottage cheese.
The lactase enzyme in liquid or tablet form is available for purchase. No prescription is needed. Take the enzyme with the lactose-containing food. Lactase will help digest the lactose so the body can absorb it.
Milk and dairy products are a major source of calcium, an essential nutrient for the growth and repair of bones and teeth throughout life. Calcium is also essential for blood to clot normally, muscles and nerves to function properly, and the heart to beat normally.
People who are lactose-intolerant don’t necessarily have to consume milk and dairy products to get the calcium they need to maintain proper nutrition.
If you have trouble consuming enough calcium-rich foods in your daily diet, talk to your healthcare provider or a dietitian about taking a calcium supplement. The amount of calcium you will need from a supplement will depend on how much calcium you are consuming through food sources.
The following foods contain calcium:
A lactose-free diet should be followed for two weeks. If symptoms have subsided after the two-week strict diet, gradually add foods with lactose back into the diet slowly and monitor tolerance. You may be able to tolerate up to 12 grams of lactose at one time. The following lists can be used to help determine what foods to try in your diet:
Lactose content of milk and milk products
The following foods contain approximately 5-8 grams of lactose:
The following foods contain approximately 0-2 grams of lactose:
The following ingredients come from milk and do not contain lactose:
General guidelines to aid in the management of your lactose intolerance upon completion of the lactose-free diet:
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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or healthcare provider. Please consult your healthcare provider for advice about a specific medical condition.
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