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Article # 1
The Lowdown on Lactose Intolerance
How Do You Know If You're Lactose Intolerant?
If you have frequent stomach pain, bloating, gas, or diarrhea, it's important
to see your doctor. Do not diagnose yourself. Your symptoms could be signs
of something more serious than lactose intolerance. Your doctor can
recommend a simple test to determine if you are lactose intolerant.
If you have lactose intolerance, your body can't fully digest the amount of
lactose (the major sugar found in milk) consumed. Most people who have
trouble digesting lactose have low levels of an enzyme called lactase (i.e.,
lactose maldigesters).
Myths About Lactose Intolerance
Myth: If you are diagnosed with low levels of the enzyme lactase, you
should avoid all milk and milk products.
Fact: Many lactose maldigesters (people with low lactase levels) can drink 1
cup of milk a day with a meal - or up to 2 cups; one with breakfast, the
other with dinner - without developing symptoms. Others, however, are
affected after eating much smaller amounts of lactose. Also, the type of milk
or milk product and the conditions under which it is eaten can affect how
well you handle lactose. See the "Rules to Live By" section for tips on how to
reduce your chance of symptoms.
Myth: You will always get symptoms after eating foods with lactose if your
body has low levels of lactase.
Fact: Many people with low lactase levels (i.e., lactose maldigesters) don't
even know it. That's because lactose maldigesters can still digest some
lactose and will only develop symptoms when they eat more lactose than
their enzyme level can handle.
Myth: It is not important for you to consume milk or milk products if you're
a lactose maldigester, or have been diagnosed as lactose intolerant (i.e.,
develop symptoms after a test dose of lactose).
Fact: Giving up milk and milk products is unnecessary, nutritionally unwise,
and not recommended. About 73% of the calcium in the American food
supply comes from the Milk Group. In fact, it's hard to find a better source of
readily available calcium! Plus, milk and milk products provide important
nutrients your body needs, including calcium, protein, riboflavin, vitamins A,
D (when fortified), and B12, phosphorus, magnesium, and potassium.
Research shows that people who get ample amounts of calcium may reduce
their risk of osteoporosis (weak bones that easily fracture), hypertension
(high blood pressure), and some cancers.
Myth: If your body can't absorb lactose, it also can't absorb the calcium in
Fact: Calcium is absorbed just as well whether or not you can digest lactose.
But if you have lactose intolerance (symptoms) and cut back on milk (and
therefore calcium), you may be putting yourself at greater risk of
osteoporosis. Your health care provider can help you come up with strategies
for including calcium-rich milk and milk-products in your diet.
Myth: Lactose is found only in milk and milk products.
Fact: Lactose is found in many foods you probably wouldn't suspect,
including bread and other baked goods, processed breakfast cereals, and
instant potato soups. A food contains lactose if the ingredient list mentions
any of the following words: milk, whey, curds, milk by-products, dry milk
solids, or nonfat dry milk powder. Lactose may also be present in small
amounts in prescription drugs and over-the-counter medications. Ask your
doctor or registered dietician if the medication you are taking contains
Did You Know?
Most adults need 1,000 mg of calcium a day. You can meet your needs by
consuming at least 3 servings from the Milk Group each day.
Many individuals who have trouble digesting lactose can drink at least 1 cup
of milk with a meal such as breakfast or dinner without any symptoms.
Six Rules To Live By
Easy Ways To Enjoy Milk And Milk Products If You're Lactose Intolerant
1. Pair the Milk. Drink milk in servings of 1 cup or less along with meals or
snacks. If you still get symptoms, try even smaller amounts more often
throughout the day.
2. Older is Wiser. Try natural aged or ripened cheeses such as Swiss and
cheddar. Not only do these cheeses contain little, if any, lactose, but they
are an important source of calcium and other essential nutrients.
3. Get a Little "Culture." Choose yogurts that carry the "live and active
cultures" seal. These "friendly" cultures act like lactase since they "break
down" the lactose in the digestive tract. If you're having sweet acidophilus
milk, cultured buttermilk, or yogurt without active cultures, have small
servings with meals or other foods.
4. Chill Out. Small (1/2 cup) servings of ice cream or frozen yogurt can cool
you down - usually without causing symptoms.
5. Reduce It. You can buy lactose-reduced and lactose-free milk and milk
products in many grocery stores. Feeling adventuresome? You can make
your own lactose-reduced milk by treating it with a lactase enzyme available
in many pharmacies. Or, take a lactase tablet just before eating a lactosecontaining food.
6. Go to the Pros. Call your doctor, registered dietician, or other health
care provider for help in finding ways to enjoy milk and milk products if you
have difficulty digesting lactose.
On The Lookout For Lactose?
Lactose (grams)
Milk (all types), 1 cup
Yogurt, 1 cup
Ice Cream, 1/2 cup
Cottage Cheese, 1/2 cup
American Cheese, 1 1/2 oz
Swiss Cheese, 1 1/2 oz
Cheddar Cheese, 1 1/2 oz
Process Cheese, 2 oz
Sardines, 3 oz
Salmon w/ Bones (canned), 3 oz
Tofu (processed w/ calcium salts), 3 oz
Broccoli (cooked), 1/2 cup
Collard Greens (cooked), 1/2 cup
Source: National Digestive Diseases Information Clearinghouse. Lactose
Intolerance, 1994.
Help! My Medication Is Making Me Sick!
The Bad News: Taking some medications, radiation treatments, having
gastric surgery, or sometimes just having the flu may make it harder to
digest lactose.
The Good News: It's only temporary. Once the flu is gone or you are no
longer taking medications, you can generally handle lactose again.
LactoseMilk Sugar
Lactose Intolerance
Article #2
What is lactose intolerance?
Lactose intolerance is an inability to digest and absorb lactose (the sugar in milk) that results in
gastrointestinal symptoms when milk or products containing milk are drunk or eaten.
What causes lactose intolerance?
Lactose is a larger sugar that is made up of two smaller sugars, glucose and galactose. In order for
lactose to be absorbed from the intestine and into the body, it must first be split into glucose and
galactose. The glucose and galactose then are absorbed by the cells lining the small intestine. The
enzyme that splits lactose into glucose and galactose is called lactase, and it is located on the surface of
the cells that line the small intestine.
Lactose intolerance is caused by reduced or absent activity of lactase that prevents the splitting of lactose
(lactase deficiency). Lactase deficiency may occur for one of three reasons, congenital, secondary or
Congenital causes of lactose intolerance
Lactase deficiency may occur because of a congenital absence (absence from birth) of lactase due to a
mutation in the gene that is responsible for producing lactase. This is a very rare cause of lactase
deficiency, and the symptoms of this type of lactase deficiency begin shortly after birth.
Secondary causes of lactose intolerance
Another cause of lactase deficiency is secondary lactase deficiency. This type of deficiency is due to
diseases that destroy the lining of the small intestine along with the lactase. An example of such a
disease is celiac sprue.
Developmental causes of lactose inotlerance
The most common cause of lactase deficiency is a decrease in the amount of lactase that occurs after
childhood and persists into adulthood, referred to as adult-type hypolactasia. This decrease is genetically
programmed, and the prevalence of this type of lactase deficiency among different ethnic groups is highly
variable. Thus, among Asian populations it is almost 100%, among American Indians it is 80%, and
among blacks it is 70%; however, among American Caucasians the prevalence of lactase deficiency is
only 20%. In addition to variability in the prevalence of lactase deficiency, there also is variability in the
age at which symptoms of lactose intolerance appear. Thus, among Asian populations, the symptoms of
deficiency (intolerance) occurs around the age of 5, among Blacks and Mexican-Americans by the age of
10, and among the Finnish by age 20.
It is important to emphasize that lactase deficiency is not the same as lactose intolerance. Persons with
milder deficiencies of lactase often have no symptoms after the ingestion of milk. For unclear reasons,
even persons with moderate deficiencies of lactase may not have symptoms. A diagnosis of lactase
deficiency is made when the amount of lactase in the intestine is reduced, but a diagnosis of lactose
intolerance is made only when the reduced amount of lactase causes symptoms.
What are the symptoms of lactose intolerance?
The common symptoms of lactose intolerance are gastrointestinal, primarily, abdominal pain, diarrhea,
flatulence (passing gas), and, less commonly, abdominal bloating, abdominal distention, and nausea.
Unfortunately, these symptoms can be caused by other gastrointestinal conditions or diseases, so the
presence of these symptoms are not very good at predicting whether a person has lactase deficiency or
lactose intolerance.
Symptoms occur because the unabsorbed lactose passes through the small intestine and into the colon.
In the colon, one type of normal bacterium contains lactase and is able to split the lactose and use the
resulting glucose and galactose for its own purposes. Unfortunately, when they split the lactose into
glucose and galactose, these bacteria also release hydrogen gas. Some of the gas is absorbed from the
colon and into the body and is then excreted by the lungs in the breath. Most of the hydrogen, however, is
used up in the colon by other types of bacteria. A small proportion of the hydrogen gas is expelled and is
responsible for the increased flatus (passing gas). Some people have an additional type of bacterium in
their colons that changes the hydrogen gas into methane gas, and these people will excrete only
methane or both hydrogen and methane gas in their breath and flatus.
Not all of the lactose that reaches the colon is split and used by colonic bacteria. The unsplit lactose in
the colon draws water into the colon (by osmosis). This leads to loose, diarrheal stools.
The severity of the symptoms of lactose intolerance vary greatly from person to person. One reason for
this variability is that people have different amounts of lactose in their diet; the more lactose in the diet,
the more likely and severe the symptoms. Another reason for the variability is that people have differing
severities of lactase deficiency, that is, they may have mildly, moderately, or severely reduced amounts of
lactase in their intestines. Thus, small amounts of lactose will cause major symptoms in severely lactase
deficient people but only mild or no symptoms in mildly lactase deficient people. Finally, people may have
different responses to the same amount of lactose reaching the colon. Whereas some may have mild or
no symptoms, others may have moderate symptoms. The reason for this is not clear but may relate to
differences in their intestinal bacteria.
Elimination diet
Probably the most common way that people self-diagnose lactose intolerance is by an elimination diet, a
diet that eliminates obvious milk and milk products. There are several problems with this type of "testing."
1. Milk products are so common in prepared foods from the supermarket or restaurant that it is likely
that an elimination diet that is not rigorous (i.e., does not eliminate all milk) will still include
substantial amounts of milk. Thus, persons with severe lactase deficiency attempting an
elimination diet may be ingesting enough lactose to have symptoms and erroneously conclude
that lactose intolerance is not responsible for the symptoms.
2. People often make the assumption that they are lactose intolerant based on a short trial of
elimination. A short trial may be adequate if symptoms are severe and occurring daily, but not if
the symptoms are subtle and/or variable. In the latter case, an elimination diet may need to be
continued for weeks.
3. Because symptoms of lactose intolerance are subjective and variable, there always is the
possibility of a "placebo effect" in which people think they feel better eliminating milk when, in
fact, they are no better. With subjective symptoms such as those of lactose intolerance, a placebo
effect can be expected to occur 20-40% of the time.
If an elimination diet is to be used for diagnosing lactose intolerance, it should be a rigorous diet. A
rigorous diet requires counseling by a dietician or reading a guide to a lactose-elimination diet. The diet
also needs to be continued long enough to clearly evaluate whether or not symptoms are better. If there
is doubt about improvement on the diet, particularly if symptoms normally fluctuate in intensity over weeks
or months, repeated periods of lactose elimination should be tried until a firm conclusion can be drawn.
Elimination of all milk products should eliminate symptoms completely if lactose intolerance alone is the
cause of the symptoms.
Milk challenge
A milk challenge is a simpler way of diagnosing lactose intolerance than an elimination diet. A person
fasts overnight and then drinks a glass of milk in the morning. Nothing further is eaten or drunk for 3-5
hours. If a person is lactose intolerant, the milk should produce symptoms within several hours of
ingestion. If there are no symptoms, it is unlikely that lactose intolerance is the cause of the symptoms. It
is important for the milk that is used to be non-fat milk to eliminate the possibility that fat in the milk is the
cause of symptoms. It is not possible to eliminate the possibility that symptoms are due to milk allergy, a
very different condition than lactose intolerance; however, this is not usually confusing since allergy to
milk is rare and usually occurs in infants and young children. (If milk allergy is a consideration, pure
lactose can be used instead of milk.)
An important issue in the milk challenge is the amount of milk to use.
If a person drinks glasses of milk or ingests larger amounts of milk-containing products in their
normal diet, then a larger amount of milk should be used in the challenge, 8-16 ounces in an
adult, equivalent to one or two large glasses of milk.
If the person being tested usually does not drink glasses of milk or ingest larger quantities of milkcontaining products, there may be a problem with using 8-16 ounces of milk for testing. These
larger quantities of milk used for testing may cause symptoms, but the smaller amounts of milk or
milk products that these persons ingest in their normal diet may not be enough to cause
symptoms. Technically, they may be lactose intolerant when they are tested with larger amounts
of milk, but lactose in their normal diet cannot be responsible for their usual symptoms.
Recognition of this issue is important in interpreting the results of a milk challenge.
Breath test
The hydrogen breath test is the most convenient and reliable test for lactase deficiency and lactose
intolerance. For the breath test, pure lactose, usually 25 grams (the equivalent of 16 oz of milk), is
ingested with water after an overnight fast. In persons who are lactose intolerant, the lactose that is not
digested and absorbed in the small intestine reaches the colon where the bacteria split the lactose into
glucose and galactose and produce hydrogen (and/or methane) gas. Small amounts of the hydrogen and
methane are absorbed from the colon into the blood and then travel to the lungs where they are excreted
in the breath. Samples of breath are collected every 10 or 15 minutes for 3-5 hours after ingestion of the
lactose, and the samples then are analyzed for hydrogen and/or methane. If hydrogen and/or methane is
found in the breath, it means that the small intestine of the person having the test was unable to digest
and absorb all of the lactose. He or she is lactase deficient. The amount of hydrogen or methane excreted
in the breath is roughly proportional to the degree of lactase deficiency, that is, the larger the amount of
hydrogen and/or methane produced, the greater the deficiency. The amount of hydrogen and/or methane
in the breath, however, is not proportional to the severity of the symptoms. In other words, a person who
produces little hydrogen and/or methane may have more severe symptoms than a person who produces
a large amount hydrogen and/or methane.
The breath test is the best test for determining lactase deficiency and lactose intolerance, but it has
several weaknesses. The first is that it is a long, boring test. The second is that it suffers from the same
issue as the milk challenge test with respect to the quantity of lactose that should be used. (See previous
discussion.) Lastly, the breath test can be falsely abnormal when there is spread of bacteria from the
colon into the small intestine, a condition called bacterial overgrowth of the small bowel. When
overgrowth occurs, the bacteria that have moved up into the small intestine get to the lactose in the
intestine before it has time to be digested and absorbed normally, and these bacteria produce hydrogen
and/or methane. This may lead erroneously to a diagnosis of lactose intolerance. Other conditions also
interfere with the breath test. Thus, diseases that markedly speed up transit of lactose through the small
intestine prevent lactose from being fully digested and absorbed, leading to a misdiagnosis of lactose
intolerance. Recent treatment with antibiotics can suppress colonic bacteria and their production of
hydrogen or methane and lead to a misdiagnosis of lactose tolerance. Fortunately, these latter conditions
are uncommon and usually can be anticipated on the basis of a person's history or symptoms.
Blood glucose test
The blood glucose test is an older test for lactase deficiency and lactose intolerance. For the blood
glucose test, lactose is ingested (usually 0.75 to 1.5 gm of lactose per kg of body weight) after an
overnight fast, and serial blood samples are drawn and analyzed for glucose. If the level of blood glucose
rises more than 25 mg/100ml, it means that the lactose has been split in the intestine and the resulting
glucose has been absorbed into the blood. This implies that lactase levels are normal. Unfortunately, the
blood glucose test, though simple in principle, requires the collection of multiple samples of blood.
Moreover, the test has many real and potential problems, the most common of which is false positive
tests, that is, an abnormal test in people who have normal lactase levels and no lactose intolerance. For
these reasons, the blood glucose test is not often used.
Stool acidity test
The stool acidity test is a test for lactase deficiency in infants and young children. For the stool acidity
test, the infant or child is given a small amount of lactose orally. Several consecutive stool samples then
are tested for acidity. With a deficiency of lactase, unabsorbed lactose enters the colon and is split into
glucose and galactose. Some of the glucose and galactose is broken down by the bacteria into acids, for
example, lactic acid. Lactic acid turns the stool acidic. Therefore, a lactase deficient infant or child will
develop an acidic stool following the test dose of lactose.
Despite the availability of the stool acidity test, the superiority of breath testing has led to modifications in
equipment for collecting breath samples that makes it easier to do breath testing in young children and
even infants. As a result, the stool acidity test is not done frequently.
Intestinal biopsy
The most direct test for lactase deficiency is biopsy of the intestinal lining with measurement of lactase
levels in the lining. The biopsy can be obtained by endoscopy or by special capsules that are passed
through the mouth or nose and into the small intestine. The analysis of lactase levels in the biopsy
requires specialized procedures that are not often available, and, as a result, lactase levels are not often
measured except for research purposes.
What are the sources of lactose in the diet?
Although milk and foods made from milk are the only natural sources of lactose, lactose often is "hidden"
in prepared foods to which it has been added. 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
Lunch meats (except those that are kosher)
Salad dressings
Candies and other snacks
Mixes for pancakes, biscuits, and cookies
Some products labeled nondairy, such as powdered coffee creamer and whipped toppings, also may
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 to food sources, lactose can be "hidden" in medicines. Lactose is used as the base for more
than 20% of prescription drugs and about 6% of over-the-counter drugs. 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.
How is lactose intolerance treated?
Dietary changes
The most obvious means of treating lactose intolerance is by reducing the amount of lactose in the diet.
Fortunately, most people who are lactose intolerant can tolerate small or even moderate amounts of
lactose. It often takes only elimination of the major milk-containing products to obtain sufficient relief from
their symptoms. Thus, it may be necessary to eliminate only milk, yogurt, cottage cheese, and ice cream.
Though yogurt contains large amounts of lactose, it often is well-tolerated by lactose intolerant people.
This may be so because the bacteria used to make yogurt contain lactase, and the lactase is able to split
the lactose during storage of the yogurt as well as after the yogurt is eaten (in the stomach and intestine).
Yogurt also has been shown to empty more slowly from the stomach than an equivalent amount of milk.
This allows more time for intestinal lactase to split the lactose in yogurt, and, at least theoretically, would
result in less lactose reaching the colon.
Most supermarkets carry milk that has had the lactose already split by the addition of lactase. Substitutes
for milk also are available, including soy and rice milk. Acidophilus-containing milk is not beneficial since it
contains as much lactose as regular milk, and acidophilus bacteria do not split lactose.
For individuals who are intolerant to even small amounts of lactose, the dietary restrictions become more
severe. Any purchased product containing milk must be avoided. It is especially important to eliminate
prepared foods containing milk purchased from the supermarket and dishes from restaurants that have
Another means to reduce symptoms of lactose intolerance is to ingest any milk-containing foods during
meals. Meals (particularly meals containing fat) reduce the rate at which the stomach empties into the
small intestine. This reduces the rate at which lactose enters the small intestine and allows more time for
the limited amount of lactase to split the lactose without being overwhelmed by the full load of lactose at
once. Studies have shown that the absorption of lactose from whole milk, which contains fat, is greater
than from non-fat milk, perhaps for this very reason. Nevertheless, the substitution of whole milk or yogurt
for non-fat milk or yogurt does not seem to reduce the symptoms of lactose intolerance.
Lactase enzyme
Caplets or tablets of lactase are available to take with milk-containing foods.
Some people find that by slowly increasing the amount of milk or milk-containing products in their diets
they are able to tolerate larger amounts of lactose without developing symptoms. This adaptation to
increasing amounts of milk is not due to increases in lactase in the intestine. Adaptation probably results
from alterations to the bacteria in the colon. Increasing amounts of lactose entering the colon change the
colonic environment, for example, by increasing the acidity of the colon. These changes alter the way in
which the colonic bacteria handle lactose. For example, the bacteria produce less gas. There also may be
a reduction in the secretion of water and, therefore, less diarrhea.
Calcium and vitamin D supplements
Milk and milk-containing products are the best sources of dietary calcium, so it is no wonder that calcium
deficiency is common among lactose intolerant persons. This increases the risk and severity of
osteoporosis and the resulting bone fractures. It is important, therefore, for lactose intolerant persons to
supplement their diets with calcium. A deficiency of vitamin D also causes disease of the bones and
fractures. Milk is fortified with vitamin D and is a major source of vitamin D for many people. Although
other sources of vitamin D can substitute for milk, it is a good idea for lactose-intolerant persons to take
supplemental vitamin D to prevent vitamin D deficiency.
What are the long-term consequences of lactose intolerance?
The important long-term health consequence of lactose intolerance is calcium deficiency that leads to
osteoporosis. Less commonly, vitamin D deficiency may occur and compound the bone disease. Both of
these health issues can be prevented easily by calcium and vitamin D supplements. The real problem is
that many lactose intolerant people who consciously or unconsciously avoid milk do not realize that they
need supplements. For more about the subject of calcium and vitamin D deficiencies, please see the
Vitamins and Calcium Supplements and Osteoporosis articles.
What is new in lactose intolerance?
It is now possible to test the DNA of individuals to make a diagnosis of lactose intolerance. This is likely to
be an important research tool for studying lactase deficiency and lactose intolerance. It is still too early to
know how helpful this sophisticated testing will be in the clinical evaluation and treatment of patients. It is
an expensive test.
In 1998, scientists were able to make lactose intolerant rats tolerant of lactose by transferring the gene for
lactase to their intestinal lining cells. It is unlikely that this type of gene therapy will find much of an
application in people. Nevertheless, it is a fascinating example of what science can accomplish.
Questions for Article readings:
Article #1:
1. What are the symptoms of Lactose Intolerance?
2. What is Lactose?
3. What is Lactase?
4. Can people, who are Lactose Intolerant, have milk or
milk products?
5. What nutrients are found in milk products?
6. What diseases are related to low levels of these
7. Explain one of the “Six Rules To Live By.”
8. What is a “culture”?
9. Can someone have “temporary lactose intolerance”?
Explain how.
Article #2:
1. What two sugars make up Lactose?
2. Briefly describe the three ways lactose intolerance can
occur in an individual.
3. Distinguish between lactase deficiency and lactose
4. List 2 reasons why self-diagnosis of lactose intolerance, by
way of elimination diet, is a bad idea.
5. List 5 ways of testing for lactose intolerance. If you suspect
that you are lactose intolerant, which test would you
choose. Explain the pros and cons of the test you selected.
6. List 4 ‘hidden’ sources of lactose in your diet.
7. Explain ways lactose intolerance can be treated.
8. What are the long term consequences of lactose