What Is Lactose Intolerance?
Lactose is a sugar that naturally occurs in milk. Someone is considered "lactose intolerant" when the small intestine cannot produce enough of the enzyme that digests lactose called lactase.
In primary lactose intolerance, the enzyme is produced during childhood but declines substantially by adulthood. Secondary lactose intolerance occurs when the small intestine has been damaged by illness or exposure to certain medical treatments. Lactose intolerance most often affects adults of African, Asian, Hispanic, and Native American descent.
Gastrointestinal symptoms, such as gas, bloating, diarrhea, and sometimes nausea and vomiting, occur roughly two hours after consuming dairy products, such as milk, ice cream, or yogurt. Lactose intolerance is not dangerous, but the uncomfortable symptoms can interfere with quality of life. Dairy products are an important source of nutrients and their avoidance can lead to nutrient deficiencies.
Treatment typically consists of simply avoiding lactose-containing foods, or replacing the enzyme in order to break down the lactose.
You can treat these symptoms yourself by trying to limiting consumption of dairy products or switching to non-dairy alternatives. You can also take a pill that has the enzyme that you are missing.
Lactose Intolerance Symptoms
Symptoms of lactose intolerance typically start two hours following ingestion of lactose-containing foods . However, avoidance of dairy products can result in deficiencies of calcium and vitamin D. The symptoms of lactose intolerance are harmless but can be very uncomfortable. They differ slightly depending on the amount of lactose consumed.
Following small ingestions of lactose, you may experience:
- Abdominal pain: Characterized as diffuse, crampy belly pain
- Bloating: Uncomfortable feelings of fullness
- Nausea: Sometimes accompanied by vomiting
- Gas (flatus)
Following larger ingestions of lactose, the above symptoms may occur in addition to:
- Loose stool: Watery bowel movements
- More frequent bowel movements
Lactose Intolerance Causes
Lactose intolerance mainly occurs when lactose, the main sugar found in dairy products, is unable to be absorbed directly by the intestines. Instead, the lactase enzyme, located on the border of the small intestines, breaks lactose down into glucose and galactose, which can be absorbed. When lactose is not broken down:
- The unabsorbed sugar attracts fluid into the bowels via osmosis, leading to high-volume, watery stool.
- Gut bacteria ferment the lactose and break it into smaller sugars, producing gas and further drawing fluid into the bowel.
Patterns of lactose intolerance can be described as primary, secondary, and congenital inabilities to produce lactase; however, a lifetime inability to produce lactase is rare [1,2].
Primary (adult hypolactasia)
All mammals experience a decline in lactase production from birth. In about 70 percent of adults, lactase declines to such low levels that symptoms can become present when lactose is consumed . Inadequate production of lactase in adults is the most common pattern of lactose intolerance.
Secondary (acquired hypolactasia)
Inadequate lactase production that stems from gastrointestinal illness damages the cells that produce the enzyme. Diseases associated with lactose intolerance include:
- Celiac or Tropical sprue: Inflammation of the small bowel
- Crohn's Disease: Inflammation of the GI tract
- Whipple's disease: A bacterial infection
- Severe gastroenteritis: Persistent diarrhea from an infection
- Cystic fibrosis: Associated with severe damage to the respiratory and digestive tracts
- HIV enteropathy: A change in intestinal structure and function in those with HIV
- Carcinoid syndrome: An associated carcinoid tumor that secretes problematic chemicals may be located in the GI tract
- Diabetic gastropathy: Involves various neuromuscular dysfunctions of the stomach in relation to diabetes
- Kwashiorkor: A severe nutrient deficiency
- Zollinger-Ellison Syndrome: A disease characterized by excessive production of stomach acid
- Cancer treatments: Chemotherapy and radiation therapy can damage the cells of the gut and lead to lactose intolerance
Who is most likely to be affected
Lactase deficiency is found at different rates among different groups, although, it impacts many different people worldwide [1,3]. Some persons with lactase deficiency can tolerate small amounts of lactose.
- Majority: The majority affected (60 to 100 percent) is made up of people who are Asian, such as people from Thailand, Indonesia, China, and the Koreas; Native Americans; Ashkenazi Jews; people from the Near East and Mediterranean, such as Arabs, Greeks, and Southern Italians; most people of African descent; and people from Latin America.
- Minority: The minority affected (< 30 percent) is made up of northern Europeans and Punjabi and New Delhi Indians.
Lactose Intolerance Symptom Checker
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Treatment Options and Prevention for Lactose Intolerance
Treatments for lactose intolerance involve proactively limiting symptoms as well as maintaining adequate levels of calcium and vitamin D. This may include taking supplements or altering your diet. It also may be necessary to treat underlying conditions causing lactose intolerance.
Lactose intolerance is not an allergy to milk or dairy products. Milk protein allergy is a different condition that involves the immune system. People with lactose intolerance can typically tolerate small amounts of dairy products, which are necessary for adequate nutrition.
Be mindful of lactose intake
Foods with the highest lactose content include milk, yogurt, and ice cream. Cheeses contain lactose at considerably lower levels and can be a good source of calcium for people unable to tolerate milk [3,4]. In addition to dairy products, the following prepared foods may contain small amounts of lactose that may irritate people with very low lactose tolerance . These include:
- Baked goods, including bread, pancakes, biscuits, and cookies
- Breakfast cereal
- Instant potatoes and soups
- Lunch meats
- Salad dressings
- Snack foods
- "Non-dairy" creamers, which may still contain lactose
Lactase supplements, such as Dairy Ease and Lactaid can be taken prior to consumption of dairy products to facilitate the digestion of lactose. These supplements are available over-the-counter in the U.S. The effective dose of the supplements varies from person to person and meal to meal and can be difficult to determine.
Ensure adequate calcium and vitamin D intake
Adults are recommended to consume 1200 to 1500 mg of calcium daily . Calcium intake is critical to adequate bone mineralization in children . In order to better tolerate milk, controlled consumption may be helpful:
- Practice moderation: Most people with lactose intolerance can tolerate 8 to 12 ounces of milk daily without symptoms . Additionally, milk products may be tolerated best if taken in small amounts throughout the day.
- Do not consume lactose by itself: Solid foods slow the GI tract, allowing more time for slow degradation of lactose, so intake of solid foods with dairy products may facilitate tolerable consumption .
- Choose lactose-free and reduced items: Lactose-free and lactose-reduced milk are widely available in supermarkets. They are the same as regular milk but have had the lactase enzyme added .
Non-dairy sources of calcium and vitamin D
In addition to the methods above, you can also maintain adequate levels of calcium and vitamin D with non-dairy options. Sources of these nutrients you should add to your diet include the following [2,4].
- Fish with soft bones, such as salmon and sardines
- Green, leafy vegetables, such as spinach
- Soy and rice milk
- Nuts and beans
Treatment of underlying conditions
In people with secondary lactose intolerance, treatment of underlying conditions may help reduce symptoms of lactose intolerance.
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When to Seek Further Consultation for Lactose Intolerance
If you are experiencing abdominal pain or other gastrointestinal symptoms and think you may have lactose intolerance, discuss this possibility with your physician. Your physician will ask you specific questions about your diet and symptoms and may recommend dietary changes or breath tests. It may be helpful to journal your dietary intake and timing of symptoms and show this to your physician.
If you are worried about you or your child getting adequate nutrients
If you or your child is unable to tolerate certain foods due to lactose intolerance, discuss dietary recommendations with your physician.
If you have severe abdominal pain, persistent nausea, and vomiting, or weight loss
Severe abdominal pain that interferes with daily activities, persistent nausea and an inability to tolerate eating, and weight loss require prompt evaluation to rule out potentially dangerous causes of abdominal pain and prevent complications.
If your symptoms do not improve with dietary changes
The discomfort associated with lactose intolerance should resolve with dietary changes. If your symptoms do not improve despite dietary changes, you may have another condition and require further evaluation.
Questions Your Doctor May Ask to Determine Lactose Intolerance
To diagnose this condition, your doctor would likely ask about the following symptoms and risk factors.
- Any fever today or during the last week?
- Have you lost your appetite recently?
- Have you experienced any nausea?
- Have you had any changes in your weight?
- Have you been feeling more tired than usual, lethargic or fatigued despite sleeping a normal amount?
If you've answered yes to one or more of these questions
Lactose Intolerance Symptom Checker
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- Swagerty DL, Walling A, Klein RM. Lactose intolerance. American Family Physician. 2002;65(9):1845-1851. AAFP Link
- Lactose intolerance. Mayo Clinic. Published April 21, 2018. Mayo Clinic Link
- Heyman MB. Lactose intolerance in infants, children, and adolescents. Pediatrics. 2006;11(3):online. AAP Link
- Fisher R. Lactose intolerance. National Institute of Diabetes and Digestive and Kidney Diseases. NIDDK Link
- Lactose intolerance. Johns Hopkins Medicine. Hopkins Medicine Link
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