What is Lactose
How Is Lactose Intolerance Diagnosed?
How Is Lactose Intolerance Treated?
How Is Nutrition Balanced?
What Is Hidden Lactose?
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. See figure 1. 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.
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 Native Americans and
90 percent of Asian-Americans are lactose intolerant. The condition is
least common among persons of northern European descent.
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 doctor's office.
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 down lactase 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.
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 of lactose
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. One form is a liquid for
use with milk. A few drops are added to a quart of milk, and after 24
hours in the refrigerator, the lactose content is reduced by 70 percent.
The process works faster if the milk is heated first, and adding a double
amount of lactase liquid produces milk that is 90 percent lactose free.
A more recent development is a chewable lactase enzyme tablet that helps
people digest solid foods that contain lactose. Three to six tablets are
taken just before a meal or snack.
Lactose-reduced milk and other products are available
at many 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.
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:
Amount of calcium to consume daily
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, figure 2 lists some common foods that are good sources
of dietary calcium and shows about how much lactose the foods 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 in making yogurt produce some of the lactase enzyme required
for proper digestion.
Calcium and Lactose in Common Foods
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 figure 2 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.
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:
Bread and other baked goods
Processed breakfast cereals.
Instant potatoes, soups, and breakfast drinks.
Margarine. Lunch meats (other than kosher)
Candies and other snacks
Mixes for pancakes, biscuits, and cookies.
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 item 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.