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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
The digestive tract|
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 tolerate.
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
Researchers have identified a genetic variation associated with
lactose intolerance; this discovery may be useful in developing a
diagnostic test to identify people with this condition.
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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 doctor's
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 lactose.
Normally, when lactose reaches the digestive system, the lactase
enzyme breaks it down 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 a
person's breath. Normally, very little hydrogen is detectable.
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
accuracy of the test and should be avoided before taking it. 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 the very
young because they are more prone to the 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.
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Fortunately, lactose intolerance is relatively easy to treat. No
treatment can 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 people differ in the amounts and types of
foods they can handle. For example, one person may have 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 people learning
through trial and error how much lactose they can handle.
For those who react to very small amounts of lactose or have
trouble limiting their intake of foods that contain it, lactase
enzymes are available without a prescription 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
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.
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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 shown in the following table.
||Amount of calcium to consume
daily, in milligrams (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 table that follows
lists some common foods that are good sources of dietary calcium and
shows how much lactose they contain.
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 to make yogurt produce some of the lactase
enzyme required for proper digestion.
|Calcium-fortified orange juice, 1 cup
|Sardines, with edible bones,
|Salmon, canned, with edible bones, 3 oz.
|Soymilk, fortified, 1 cup
|Broccoli (raw), 1 cup
|Orange, 1 medium
|Pinto beans, 1/2 cup
|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
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 the calcium
they contain. They also 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.
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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 even small amounts
of lactose, such as
- 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
- powdered meal-replacement supplements
Some products labeled nondairy, such as powdered coffee
creamer and whipped toppings, may also include ingredients
that are derived from milk and therefore contain lactose.
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.
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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.
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American Dietetic Association (ADA)
International Foundation for Functional Gastrointestinal
Disorders (IFFGD) Inc.
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