What Is Lactose Intolerance?
Lactose intolerance is the
inability to digest significant amounts of lactose, the
predominant sugar of milk. This inability results from a
shortage of the enzyme lactase, which is normally produced by
the cells that line the small intestine. Lactase
breaks down milk sugar into simpler forms that can then be
absorbed into the bloodstream. When there is not enough lactase
to digest the amount of lactose consumed, the results, although
not usually dangerous, may be very distressing. While not all
persons deficient in lactase have symptoms, those who do are
considered to be lactose intolerant.
Common symptoms include nausea, cramps, bloating, gas, and
diarrhea, which begin about 30 minutes to 2 hours after eating
or drinking foods containing lactose. The severity of symptoms
varies depending on the amount of lactose each individual can
Some causes of lactose intolerance are well known. For instance,
certain digestive diseases and injuries to the small intestine
can reduce the amount of enzymes produced. In rare cases,
children are born without the ability to produce lactase. For
most people, though, lactase deficiency is a condition that
develops naturally over time. After about the age of 2 years,
the body begins to produce less lactase. However, many people
may not experience symptoms until they are much older.
Between 30 and 50 million Americans are lactose intolerant.
Certain ethnic and racial populations are more widely affected
than others. As many as 75 percent of all African Americans and
American Indians and 90 percent of Asian Americans are lactose
intolerant. The condition is least common among persons of
northern European descent.
How Is Lactose Intolerance Diagnosed?
The most common tests used to measure the absorption of lactose
in the digestive system are the lactose tolerance test, the
hydrogen breath test, and the stool acidity test. These tests
are performed on an outpatient basis at a hospital, clinic, or
The lactose tolerance test begins with the individual fasting
(not eating) before the test and then drinking a liquid that
contains lactose. Several blood samples are taken over a 2-hour
period to measure the person's blood glucose (blood sugar)
level, which indicates how well the body is able to digest
Normally, when lactose reaches the digestive system, the lactase
enzyme breaks down lactose into glucose and galactose. The liver
then changes the galactose into glucose, which enters the
bloodstream and raises the person's blood glucose level. If
lactose is incompletely broken down, the blood glucose level does
not rise and a diagnosis of lactose intolerance is confirmed.
The hydrogen breath test measures the amount of hydrogen in the
breath. Normally, very little hydrogen is detectable in the
breath. However, undigested lactose in the colon is fermented by
bacteria, and various gases, including hydrogen, are produced.
The hydrogen is absorbed from the intestines, carried through
the bloodstream to the lungs, and exhaled. In the test, the
patient drinks a lactose-loaded beverage, and the breath is
analyzed at regular intervals. Raised levels of hydrogen in the
breath indicate improper digestion of lactose. Certain foods,
medications, and cigarettes can affect the test's accuracy and
should be avoided before taking the test. This test is available
for children and adults.
The lactose tolerance and hydrogen breath tests are not given to
infants and very young children who are suspected of having
lactose intolerance. A large lactose load may be dangerous for
very young individuals because they are more prone to
dehydration that can result from diarrhea caused by the lactose.
If a baby or young child is experiencing symptoms of lactose
intolerance, many pediatricians simply recommend changing from
cow's milk to soy formula and waiting for symptoms to abate.
If necessary, a stool acidity test, which measures the amount of
acid in the stool, may be given to infants and young children.
Undigested lactose fermented by bacteria in the colon creates
lactic acid and other short-chain fatty acids that can be
detected in a stool sample. In addition, glucose may be present
in the sample as a result of unabsorbed lactose in the colon.
How Is Lactose Intolerance Treated?
Fortunately, lactose intolerance is relatively easy to treat.
No treatment exists to improve the body's ability to produce
lactase, but symptoms can be controlled through diet.
Young children with lactase deficiency should not eat any foods
containing lactose. Most older children and adults need not
avoid lactose completely, but individuals differ in the amounts
and types of foods they can handle. For example, one person may suffer
symptoms after drinking a small glass of milk, while another can
drink one glass but not two. Others may be able to manage ice
cream and aged cheeses, such as cheddar and Swiss, but not other
dairy products. Dietary control of lactose intolerance depends
on each person's learning through trial and error how much
lactose he or she can handle.
For those who react to very small amounts of lactose or have
trouble limiting their intake of foods that contain lactose,
lactase enzymes are available without a prescription. Lactase enzyme tablets are available to help people digest foods that contain lactose. The tablets are taken with the first bite of dairy food. Lactase enzyme is also available as a liquid. Adding a few drops of the enzyme will convert the lactose in milk or cream, making it more digestible for people with lactose intolerance.
Lactose-reduced milk and other products are available at most
supermarkets. The milk contains all of the nutrients found in
regular milk and remains fresh for about the same length of time,
or longer if it is super-pasteurized.
How Is Nutrition Balanced?
Milk and other dairy products are a major source of nutrients
in the American diet. The most important of these nutrients is
calcium. Calcium is essential for the growth and repair of bones
throughout life. In the middle and later years, a shortage of
calcium may lead to thin, fragile bones that break easily, a
condition called osteoporosis. A concern, then, for both
children and adults with lactose intolerance, is getting enough
calcium in a diet that includes little or no milk.
In 1997, the Institute of Medicine released a report recommending new
requirements for daily calcium intake. How much calcium a person needs to maintain good health varies by age group. Recommendations from the report are as follows:
|Age group ||Amount of calcium to consume
daily, in milligrams (mg)
|0-6 months ||210 mg
|6-12 months ||270 mg
|1-3 years ||500 mg
|4-8 years ||800 mg
|9-18 years ||1,300 mg
|19-50 years ||1,000 mg
|51-70+ years ||1,200 mg
Also, pregnant and nursing women under 19 need 1,300 mg daily, while pregnant and nursing women over 19 need 1,000 mg.
In planning meals, making sure that each day's diet includes
enough calcium is important, even if the diet does not contain
dairy products. Many nondairy foods are high in calcium. Green
vegetables, such as broccoli and kale, and fish with soft,
edible bones, such as salmon and sardines, are excellent sources
of calcium. To help in planning a high-calcium and low-lactose
diet, the following chart lists some common foods that
are good sources of
dietary calcium and shows about how much lactose the foods
Recent research shows that yogurt with active cultures may be a
good source of calcium for many people with lactose intolerance,
even though it is fairly high in lactose. Evidence shows that
the bacterial cultures used in making yogurt produce some of the
lactase enzyme required for proper digestion.
Clearly, many foods can provide the calcium and other nutrients
the body needs, even when intake of milk and dairy products is
limited. However, factors other than calcium and lactose content
should be kept in mind when planning a diet. Some vegetables
that are high in calcium (Swiss chard, spinach, and rhubarb, for
instance) are not listed in the chart because the body cannot use
their calcium content. They contain substances called oxalates,
which stop calcium absorption. Calcium is absorbed and used only
when there is enough vitamin D in the body. A balanced diet
should provide an adequate supply of vitamin D. Sources of
vitamin D include eggs and liver. However, sunlight helps the
body naturally absorb or synthesize vitamin D, and with enough
exposure to the sun, food sources may not be necessary.
Some people with lactose intolerance may think they are not
getting enough calcium and vitamin D in their diet. Consultation
with a doctor or dietitian may be helpful in deciding whether
any dietary supplements are needed. Taking vitamins or minerals
of the wrong kind or in the wrong amounts can be harmful. A
dietitian can help in planning meals that will provide the most
nutrients with the least chance of causing discomfort.
What Is Hidden Lactose?
Although milk and foods made from milk are the only natural
sources, lactose is often added to prepared foods. People with
very low tolerance for lactose should know about the many food
products that may contain lactose, even in small amounts. Food
products that may contain lactose include
Calcium and Lactose in Common Foods
|Calcium-fortified orange juice,
|Sardines, with edible bones,
|Soymilk, fortified, 1 cup
|Salmon, canned, with edible bones, 3 oz.
|Broccoli (raw), 1 cup
|Pinto beans, 1/2 cup
|Orange, 1 medium
|Tuna, canned, 3 oz.
|Lettuce greens, 1/2 cup
|Yogurt, plain, low-fat, 1 cup
|Milk, reduced fat, 1 cup
|Swiss cheese, 1 oz.
|Ice cream, 1/2 cup
|Cottage cheese, 1/2 cup
| Adapted from Manual of Clinical Dietetics. 6th ed. American
Dietetic Association, 2000; and Soy Dairy Alternatives. Available
at: www.soyfoods.org. Accessed
March 5, 2002.
Some products labeled nondairy,
such as powdered coffee creamer and whipped toppings, may also
include ingredients that are derived from milk and therefore
Smart shoppers learn to read food labels with care, looking not
only for milk and lactose among the contents but also for such
words as whey, curds, milk by-products, dry milk solids, and
nonfat dry milk powder. If any of these are listed on a label,
the product contains lactose.
In addition, lactose is used as the base for more than 20
percent of prescription drugs and about 6 percent of
over-the-counter medicines. Many types of birth control pills,
for example, contain lactose, as do some tablets for stomach
acid and gas. However, these products typically affect only
people with severe lactose intolerance.
Even though lactose intolerance is widespread, it need not pose
a serious threat to good health. People who have trouble
digesting lactose can learn which dairy products and other foods
they can eat without discomfort and which ones they should
avoid. Many will be able to enjoy milk, ice cream, and other
such products if they take them in small amounts or eat other
food at the same time. Others can use lactase liquid or tablets
to help digest the lactose. Even older women at risk for
osteoporosis and growing children who must avoid milk and foods
made with milk can meet most of their special dietary needs by
eating greens, fish, and other calcium-rich foods that are free
of lactose. A carefully chosen diet, with calcium supplements if
the doctor or dietitian recommends them, is the key to reducing
symptoms and protecting future health.
- bread and other baked goods
- processed breakfast cereals
- instant potatoes, soups, and breakfast drinks
- lunch meats (other than kosher)
- salad dressings
- candies and other snacks
- mixes for pancakes, biscuits, and cookies
American Dietetic Association (ADA)
216 West Jackson Boulevard
Chicago, IL 60606-6995
Phone: (312) 899-0040
Fax: (312) 899-1979
International Foundation for Functional Gastrointestinal Disorders (IFFGD)
P.O. Box 170864
Milwaukee, WI 53217
Phone: 1-888-964-2001 or (414) 964-1799
Fax: (414) 964-7176