Lactose Intolerance

Lactose intolerance is a common digestive condition caused by the body's inability to digest and absorb lactose, a natural sugar found in dairy foods. It is caused by a lack of the enzyme lactase. Lactose intolerance is actually normal in most humans. The ability to digest lactase is found only in certain human populations.

Lactose intolerance can cause abdominal pain, gas, bloating, and diarrhea.

Lactase breaks down lactose into two simple sugars—glucose and galactose.

Other Names

• Lactase deficiency
• Lactose malabsorption
• Lactose maldigestion
• Hypolactasia

Types

There are three main types of lactose intolerance.

Primary lactose intolerance

Primary lactose intolerance, also called primary adult hypolactasia, occurs when people who were previously able to digest lactose begin experiencing digestive discomfort after eating dairy products, but with no history or signs of underlying intestinal disease. This is the most common form of lactase deficiency.

Secondary lactose intolerance

Secondary lactose intolerance is the result of a gastrointestinal disease, such as severe gastroenteritis, alcoholism or nutritional deficiencies.

Congenital lactose intolerance

Congenital (inborn) lactose intolerance is due to a lifelong complete absence of lactase. This condition is relatively rare. However, during the newborn period, it is not uncommon for secondary lactose intolerance to be misdiagnosed as congenital lactose intolerance.

Signs and Symptoms

The following are some signs and symptoms of lactose intolerance.

• Abdominal pain or cramping
• Diarrhea
• Flatulence (passing gas)
• Bloating

Symptoms are acute follow eating or drinking milk products, typically occurring within one to three hours after ingestion of excess dairy foods. They are always relieved after the dairy meal is fully digested. There is a dose response relationship between lactose consumed and the occurence and severity of symptoms. Most lactose maldigesters can tolerate one cup of milk, and tolerance is improved when milk is consumed with a meal. Large amounts of dairy cause worse symptoms. The severity of symptoms differs, possibly depending on the amount of lactase enzyme remaining in the body and how much lactose has been consumed. Symptoms also depend on whether or not the large intestine microflora are adapted to the regular consumption of milk products. Maldigesters who regularly consume milk have fewer symptoms due to efficient microfloral metabolism of lactose.

People vary in their degree of lactose intolerance. However, even children and teenagers with primary lactose intolerance can usually drink 8 ounces (1 cup) of milk without experiencing symptoms.

Some people with lactose intolerance may believe they are allergic to milk or milk products. But a milk allergy is due to the proteins in milk rather than the lactose sugar, and the conditions are not related.

Causes

Chemical structure of lactose. Source: Wikimedia Commons

Lactose intolerance is caused by a low level of the enzyme lactase. This enzyme breaks down lactose. Lactase is made in the small intestine.

Babies' bodies make large amounts of this enzyme so they can digest milk, including breast milk. Before humans became dairy farmers, most people did not continue to drink milk after childhood, so their bodies did not continue to make lactase.

People from cultures in which dairy farming occurred earliest in human history are less likely to experience lactose intolerance, as they evolved to drinking milk even after infancy. People from areas where dairy products come into the diet more recently are more likely to be unable to digest them. For instance, lactose intolerance is more common in Asian, African, African-American, Native American, and Mediterranean populations than it is among northern and western Europeans.

Lactose intolerance is sometimes seen in premature babies. This may be due to immaturity of the premature infant's gut.

Lactase deficiency may also occur as a result of intestinal diseases such as celiac disease and gastroenteritis. It may also follow bowel surgery. Temporary lactase deficiency can result from viral and bacterial infections, which may injure the cells lining the intestine. This is especially common in small children. This temporary deficiency generally gets better.

Diagnosis

A diagnosis can often be made based on the symptoms a person reports to the doctor. Often, no special tests are necessary other than a trial of a lactose-free diet to see if the symptoms stop. However, more specialized tests are sometimes done if the doctor needs to rule out other disorders. This may be necessary if a person is at risk for other disorders because of family history, the person has other medical conditions, or the person has traveled recently.

Exams and tests

Lactose tolerance test

This is the most common test used to diagnose lactose intolerance. The person generally will follow a lactose-free diet for one or two weeks. If the symptoms resolve, then the patient is instructed to eat dairy products again and see if the symptoms come back. If the symptoms do return, lactose intolerance can be diagnosed.

Test for stool-reducing substances

Lactose is a carbohydrate. When carbohydrates are not absorbed in the small intestine, the levels of certain chemicals in the stool called reducing substances rise. High levels of reducing substances may indicate a lactase deficiency. This test is generally done when it is suspected that the lactase deficiency is due to congenital reasons or due to injury to the small intestine. A stool sample is necessary.

Stool culture

This test is often done if a person has recently traveled or lives in a region where diarrheal diseases are common. The stool is examined in the lab for evidence of infection. A stool sample is necessary.

Lactose-hydrogen breath test

When carbohydrates are not absorbed correctly in the small intestine, extra hydrogen is produced. This can be measured in a person's breath. The lactose-hydrogen breath test is a simple test, but is not often used because it requires specialized equipment, an overnight fast and a lactose challenge.

Treatment

Removing milk products from the diet usually improves symptoms of lactose intolerance. To prevent calcium deficiency, though, sources of calcium should be maintained in the diet. However, it is not necessary to remove dairy products from the diet in order to eliminate symptoms of lactose intolerance.

It is important to read food labels. Lactose is also found in some non-milk products—including some beers. But, these levels of lactose are not likely to causes symptoms.

Most people with lactose intolerance do not require a lactose-free diet.

Studies show that there are several things people with lactose intolerance can do to improve tolerance.

• Drink milk in servings of one cup or less.
• Drink milk with other food, such as with breakfast cereal, instead of by itself.
• For infants younger than two years who are not breastfed, dairy-free formulas, such as soy, may be substituted. Good alternatives for toddlers are soy or rice milk. Older children may also use lactase-treated cow's milk.
• Eat dairy products other than milk, Hard cheeses contain almost no lactose and are well tolerated. Yogurts are very well tolerated due to the microbial 'lactase' that actually supplements the body's lactase. Ice creams, soft cheeses, cottage cheese and sour cream are moderately well tolerated. These foods contain a lower amount of lactose per serving compared with milk. Thus, they cause fewer symptoms. A few processed dairy foods such as ice milk and frozen yogurt may have large amounts of whey, and thus lactose. These foods might we less well tolerated depending on the manufacturing process.
• Consider lactose-free milk and milk products, which have the same amount of calcium as regular milk.
• Consider over-the-counter pills or drops that contain lactase, which can eliminate symptoms altogether. Lactase enzymes can be added to regular milk or may be taken in capsule or chewable tablet form.
• Consume calcium-fortified foods such as orange juice with added calcium, soy beverages with added calcium, and some fortified breads and breakfast cereals.
• Some non-dairy foods, such as spinach and broccoli, are also healthy sources of calcium. However, the body absorbs less calcium from these foods compared to milk or milk products.
• Experts suggest that the preferred source of calcium is through calcium-rich foods rather than supplements.^[1] However, if calcium cannot be adequately obtained through the diet, calcium supplements can be given.

Other Sources of Dietary Calcium

Although milk is an abundant source of calcium, calcium can be found in many other foods. Non-dairy sources of calcium include:

• Cooked soybeans
• Soy milk with added calcium
• Tofu with added calcium
• Sardines
• Canned salmon with bones
• Nutrition bars
• Orange juice with added calcium
• Broccoli
• Green, leafy vegetables such as spinach
• Almonds
• Flour tortillas
• Corn tortillas

Prevention

Lactose intolerance symptoms can be avoided with simple dietary management. The best approach to avoiding symptoms and maintaining a healthy diet with adequate calcium is actually to continue to consume dairy foods daily at meal time in moderate amounts. This approach 'trains' the intestinal bacteria to assist the body in digesting lactose. Do not overdo it. One serving per meal is a good target. If symptoms result, reduce the serving size.

Living with Lactose Intolerance

Lifestyle changes

Persons with lactose intolerance will need to pay close attention to their diets, particularly processed foods, which may contain lactose in unexpected places.

Chances of Developing Lactose Intolerance

An estimated 30 to 50 million American adults are lactose intolerant.^[2] The pattern of primary lactose intolerance appears to have a genetic component, and specific populations show high levels of intolerance, including approximately 95% of Asians, 60%–80% of African Americans and Ashkenazi Jews, 80%–100% of American Indians, and 50%–80% of Hispanics. Lactose intolerance is least common among people of northern European origin, who have a lactose intolerance prevalence of only about 2%.^[3]

Approximately 30 million American adults have some degree of lactose intolerance by age 20. Lactose intolerance is not common in young children because most people are born with enough lactase. However, in some people, the amount of lactase in their body drops as they age.

Research shows that lactase is high at birth in all infants regardless of race or ethnicity, but wanes by ages five to seven in non-Caucasians and other populations that don't traditionally include dairy products in their diets.^[4]. Lactose intolerance can begin at different times in life. In Caucasians, it usually starts to affect children older than age five. In African-Americans, lactose intolerance often occurs as early as age two.

Related Problems

Complications

Not having milk in the diet usually results in a shortage of calcium, and also puts a person at risk for lower levels of vitamins A and D, riboflavin, phosphorus, and protein. Weight loss, malnutrition, and stunted growth can result. Although many non-dairy foods, particularly enriched foods, have plenty of calcium, individuals who avoid dairy foods do eat much less calcium than those who include dairy foods.

Controversy

In the U.S. there has been controversy regarding food guidelines. Since many American ethnic minorities, including African Americans and Asian Americans, are unable to digest milk, the governmental advice and advertising campaigns stating that everyone should consume it has struck some commentators as racist.^[5] However, the evidence is clear that lactose intolerance is relatively easily managed by simple dietary changes (single servings of milk with meals, yogurts) and individuals who avoid milk eat less calcium, have lower bone densities and are at risk for osteoporosis.

References

1. ↑ National Institutes of Health. Optimal Calcium Intake. NIH Consens Statement Online 1994 June 6-8; 12(4):1-31.
2. ↑ National Institute of Diabetes and Digestive and Kidney Diseases, NIH, DHHS. Digestive Disease Statistics.
3. ↑ Swagerty DL, Walling AD, Klein RM. Lactose intolerance. Am Fam Physician. 2002; 65(2): 1845-1850. Erratum in Am Fam Physician. 2003 Mar 15;67(6):1195. Abstract | Full Text | Patient Handout
4. ↑ American Academy of Pediatrics, Committee on Nutrition. The practical significance of lactose intolerance in children: supplement. Pediatrics. 1990; 86: 643-644.
5. ↑ Suellentrop C. Milk: How a wholesome drink became a villain. Slate. June 18, 2004.

External Links

National Digestive Diseases Information Clearinghouse (NDDIC): Why Does Milk Bother Me?

American Academy of Pediatrics:

• Committee on Nutrition. Calcium requirements of infants, children, and adolescents. Pediatrics. 1999; 104(5): 1152-1157.
• Heyman, M. Lactose Intolerance in Infants, Children, and Adolescents. Pediatrics; 2006; 118(3): 1279-1286.
  • Parenting Corner Q&A: Lactose Intolerance

USDA: Food Surveys Research Group

Food Sources of Calcium, both non-dairy and dairy

Procon.org, a look at the pros and cons of milk drinking without a biased perspective