Lactose Intolerance
Lactose intolerance
Definition
Lactose intolerance refers to the inability of the body to digest lactose.
Description
Lactose is the predominant form of sugar present in milk. The enzyme lactase, which is normally produced by cells lining the small intestine, breaks down lactose into substances that can be absorbed into the bloodstream. When dairy products are ingested, the lactose reaches the digestive system and is broken down by lactase into the simpler sugars glucose and galactose, which can then be absorbed into the bloodstream. Lactose intolerance occurs when, due to a deficiency of lactase, lactose is not completely broken down and consequently blood sugar levels do not rise. While not usually a dangerous condition, lactose intolerance can cause severe discomfort.
Lactose intolerance is also referred to as lactase deficiency, milk intolerance, dairy product intolerance, or disaccharidase deficiency.
Demographics
From 30 to 50 million Americans suffer from the symptoms of lactose intolerance by the age of 20. People from cultures in which adult consumption of milk and milk products occurred earliest are less likely to be lactose intolerant than people from areas where dairy farming began more recently. The prevalence of deficiency in production of the lactase enzyme, therefore, varies among different ethnic groups. Among Asian populations it is almost 100 percent, with symptoms occurring around the age of five; among Native Americans it is 80 percent; among blacks it is 70 percent, with symptoms appearing by the age of 10; and among American Caucasians, the prevalence of lactose intolerance is only 20 percent. However, individuals who are mildly or moderately deficient in the production of the lactase enzyme may not exhibit symptoms of lactose intolerance.
Causes and symptoms
Lactose intolerance can be caused by some diseases of the digestive system (for example, celiac sprue and gastroenteritis ) and by injuries to the small intestine that result in a decreased production of lactase. While rare, some children are also born unable to produce the enzyme. For most people, however, lactase deficiency develops naturally because, after about two years of age, the body produces less lactase. Before humans became dairy farmers, they usually did not continue to drink milk, so their bodies did not produce lactase after early childhood.
Symptoms of lactose intolerance include nausea , cramps, diarrhea , floating and foul-smelling stools, bloating, and intestinal gas. The symptoms usually occur between 30 minutes to two hours after eating or drinking lactose-containing foods. A child may also exhibit weight loss, slow growth, and malnutrition .
When to call the doctor
If a child develops symptoms of lactose intolerance, the doctor should be consulted concerning dietary substitutions.
Diagnosis
To diagnosis lactose intolerance, usually healthcare professionals measure the absorption of lactose in the digestive system by using the lactose tolerance test, the hydrogen breath test, or the stool acidity test. Each of these can be performed as an outpatient in a hospital, clinic, or doctor's office.
Children who are to take the lactose tolerance test must fast before being tested. They then drink a lactose-containing liquid for the test; medical personnel take blood samples during the next two hours to measure the children's blood glucose level. The blood glucose level, or blood sugar level, indicates how well the body is digesting the lactose. A diagnosis of lactose intolerance is confirmed when blood glucose level does not rise. This test is not administered to infants and very young children because of the risk of dehydration from drinking the lactose-containing liquid, which can cause diarrhea in those who are lactose intolerant, resulting in dehydration.
Hydrogen is usually detected only in small amounts in the breath. However, when undigested lactose found in the colon is fermented by bacteria, hydrogen in the breath is produced in greater quantities. The hydrogen is exhaled after being absorbed from the intestines and carried through the bloodstream to the lungs. The hydrogen breath test involves having the child drink a lactose-containing beverage. Healthcare professionals monitor the breath at regular intervals to see if the hydrogen levels rise, which indicates improper lactose digestion. Children taking the test who have had certain foods, medications, or cigarettes before the test may get inaccurate results. While the test is useful for children and adults, infants and young children should not take it because of the risk of dehydration from diarrhea in those who are lactose intolerant.
The stool acidity test measures the amount of acid in the stool. This is a safe test for newborns and young children. The test detects lactic acid and other short-chain fatty acids from undigested lactose fermented by bacteria in the colon. Glucose may also be found in the stool sample, resulting from unabsorbed lactose in the colon.
Some parents may try to self-diagnose lactose intolerance in their child by using an elimination diet , a diet that eliminates obvious milk and milk products. However, because there are so many food products that may contain hidden sources of milk, such a diet should be supervised by a dietician or developed by following a guide to a lactose-eliminating diet. A simpler way to self-diagnose lactose intolerance is by a milk challenge. The child fasts overnight, drinks a glass of milk in the morning, and then fasts for the next three to five hours. If the child is lactose intolerant, the child should experience symptoms within several hours. If symptoms do occur, the child should be evaluated by a healthcare professional to rule out the possibility of a milk allergy. However, milk allergies are rare and usually only occurs in infants and young children.
Treatment
Since there is no treatment that can improve the body's ability to produce lactase, treatment for lactose deficiency is focused on controlling the diet.
Most children affected by lactose intolerance do well if they limit their intake of lactose-containing food and drinks. Individuals differ in the amounts they can handle before experiencing symptoms. Many children may only need to eliminate major milk-containing products from their diet, while others who are intolerant to even small amounts of lactose may be required to follow severe dietary restrictions.
Foods that contain lactose include milk, low-fat milk, skim milk, chocolate milk, buttermilk, sweetened condensed milk, dried whole milk, instant nonfat dry milk, low-fat yogurts, frozen yogurt, ice cream, ice milk, sherbet, cheese, cottage cheese, low-fat cottage cheese, cream, and butter. Other foods that may contain hidden lactose are: nondairy creamers, powdered artificial sweeteners, foods containing milk power or nonfat milk solids, bread, cake, margarine, creamed soups, pancakes, waffles, processed breakfast cereals, salad dressings, lunch meats, puddings, custards, confections, and some meat products. Lactose is also used as the base for more than 20 percent of prescription drugs and 6 percent of over-the-counter drugs.
For infants younger than two years of age, soy formulas are adequate substitutes for milk. Toddlers may drink rice or soymilk, while older children who are sensitive to lactose can take lactase enzymes, which are available without a prescription. Using the liquid form of lactase enzymes, children can add a few drops in their milk, put the milk in the refrigerator and drink it after 24 hours, when the lactase enzymes have reduced the lactose content by 70 percent. If the milk is heated first and double the amount of lactase liquid enzymes is added, the milk will be 90 percent lactose-free. Supermarkets also carry lactose-reduced milk and other products, which contain nutrients found in the regular products but without the lactose.
In the early 2000s, researchers have developed a chewable lactase enzyme tablet. Taking three to six tablets just before eating helps some children digest lactose-containing solid foods.
Nutritional concerns
Eliminating milk from the diet can result in deficiencies of calcium, vitamin D, riboflavin, and protein. Milk substitutes for children are a necessity, as other sources of calcium are required. Fermented milk products such as yogurt are often tolerated. Buttermilk and cheeses have less lactose than milk. Goat's milk can sometimes be tolerated but should be consumed with meals.
Prognosis
Lactose intolerance is easy to manage and is not considered dangerous. People of all ages, but especially children, have to replace the calcium that is lost by cutting back on milk products; this can be accomplished by taking supplements and eating calcium-rich foods, such as broccoli, kale, canned salmon with bones, calcium-fortified foods, and tofu. They may also add lactase enzymes to dairy products to reduce lactose content as well as use lactose-reduced dairy products. Many children who suffer with lactose intolerance are able to continue eating some milk products.
Prevention
Often lactose intolerance is a natural occurrence that cannot be avoided. However, people can prevent symptoms by managing the condition with diet and lactase supplements.
Parental concerns
Parents must guard the health of a child who is lactose intolerant by carefully managing the child's diet to avoid foods that will result in symptoms while providing foods that contain necessary nutrients for the child's health and growth.
KEY TERMS
Galactose —One of the two simple sugars (glucose is the other one) that makes up the protein, lactose, found in milk. Galactose can be toxic in high levels.
Glucose —A simple sugar that serves as the body's main source of energy.
Lactase —The enzyme produced by cells that line the small intestine that allows the body to break down lactose.
Lactose —A sugar found in milk and milk products.
Resources
BOOKS
Dobler, Merri Lou. Lactose Intolerance Nutrition Guide. Chicago, IL: American Dietetic Association, 2004.
The Official Patient's Sourcebook on Lactose Intolerance: A Revised and Updated Directory for the Internet Age. San Diego, CA: Icon Health Publications, 2002.
ORGANIZATIONS
American Dietetic Association. 120 South Riverside Plaza, Suite 2000 Chicago, IL 60606–6995. Web site: <www.eatright.org/Public/>.
Judith Sims Lisette Hilton
Lactose Intolerance
Lactose Intolerance
Definition
Lactose intolerance refers to the inability of the body to digest lactose.
Description
Lactose is the form of sugar present in milk. The enzyme lactase, which is normally produced by cells lining the small intestine, breaks down lactose into substances that can be absorbed into the bloodstream. When dairy products are ingested, the lactose reaches the digestive system and is broken down by lactase into the simpler sugars glucose and galactose. The liver changes the galactose into glucose, which then enters the bloodstream and raises the blood glucose level. Lactose intolerance occurs when, due to a deficiency of lactase, lactose is not completely broken down and the glucose level does not rise. While not usually dangerous, lactose intolerance can cause severe discomfort.
From 30 to 50 million Americans suffer from the symptoms of lactose intolerance, but not everyone who is deficient in lactase experiences symptoms. Experts believe that 75% of the adult population worldwide does not produce enough lactase and is at risk for some or all of the symptoms of lactose intolerance.
Causes and symptoms
Lactose intolerance can be caused by some diseases of the digestive system and by injuries to the small intestine that result in a decreased production of lactase. While rare, some children are also born unable to produce the enzyme. For many, however, lactase deficiency develops naturally because, after about two years of age, the body produces less lactase.
Symptoms include nausea, cramps, diarrhea, bloating and gas. The symptoms usually occur between 30 minutes to two hours after eating or drinking lactose-containing foods.
Diagnosis
Usually, health care professionals measure the absorption of lactose in the digestive system by using the lactose tolerance test, hydrogen breath test or stool acidity test. Each of these can be performed outpatient, through a hospital, clinic or doctor's office.
People taking the lactose tolerance test must fast before being tested. They then drink a lactose-containing liquid for the test and medical personnel take blood samples during the next two hours to measure the patient's blood glucose level. The blood glucose level, or blood sugar level, indicates how well the body is digesting the lactose. A diagnosis of lactose intolerance is confirmed when blood glucose level does not rise. This test is not administered to infants and very young children because they are more prone to dehydration, which can result from diarrhea from the liquid.
Health care professionals measure the amount of hydrogen in the breath using the hydrogen breath test. Hydrogen is usually detected only in small amounts in the breath. However when undigested lactose found in the colon is fermented by bacteria, hydrogen in the breath is produced in greater quantities. The hydrogen is exhaled after being absorbed from the intestines and carried through the bloodstream to the lungs. The hydrogen breath test involves having the patient drink a lactose-containing beverage. Health care professionals monitor the breath at regular intervals to see if the hydrogen levels rise, which indicates improper lactose digestion. People taking the test who have had certain foods, medications or cigarettes before the test may get inaccurate results. While the test is available to children and adults, newborns and young children should not have it because of the risk of dehydration from drinking the beverage that can cause diarrhea in those who are lactose intolerant.
A stool acidity test measures the amount of acid in the stool. This is a safe test for newborns and young children. The test detects lactic acid and other short-chain fatty acids from undigested lactose fermented by bacteria in the colon. Glucose might also be in the stool sample, resulting form unabsorbed lactose in the colon.
Treatment
Pediatricians might recommend that parents of newborns and very young children who are suspected of having lactose intolerance simply change from cow's milk to a soya formula. Since there is no treatment that can improve the body's ability to produce lactase, lactose deficiency treatments instead, are focused on controlling the diet.
Most people affected by lactose intolerance do well if they limit their intake of lactose foods and drinks. People differ in the amounts they can handle before experiencing symptoms. Some have to stop lactose completely. People who are sensitive after ingesting small amounts of lactose can take lactase enzymes, which are available without a prescription. Using the liquid form, people can add a few drops in their milk, put the milk in the refrigerator and drink it after 24 hours, when the lactase enzymes have worked to reduce the lactose content by 70%. If the milk is heated first and double the amount of lactase liquid is added, the milk will be 90 percent lactose free. Recently, researchers have developed a chewable lactase enzyme tablet. By taking three to six tablets just before eating, the tablets help people digest lactose-containing solid foods. Supermarkets also carry lactose-reduced mild and other products, which contain the needed nutrients found in the regular products but without the lactose.
Foods that contain lactose are milk, low-fat milk, skim milk, chocolate milk, buttermilk, sweetened condensed milk, dried whole milk, instant nonfat dry milk, low-fat yogurts, frozen yogurts ice cream, ice milk, sherbet, cheese, cottage cheese, low-fat cottage cheese, cream and butter. Other foods that may contain hidden lactose are: nondairy creamers, powdered artificial sweeteners, foods containing milk power or nonfat milk solids, bread, cake, margarine, creamed soups, pancakes, waffles, processed breakfast cereals, salad dressings, lunch meats, puddings, custards, confections and some meat products.
Prognosis
Lactose intolerance is easy to manage. People of all ages however, especially children, have to replace the calcium lost by cutting back on milk products by taking supplements and eating calcium-rich foods, such as broccoli, kale, canned salmon with bones, calcium-fortified foods and tofu. Many people who suffer with lactose intolerance will be able to continue eating some milk products. The condition is not considered dangerous.
Prevention
Often, lactose intolerance is a natural occurrence that cannot be avoided. However, people can prevent symptoms by managing the condition with diet and lactase supplements.
KEY TERMS
Galactose— Simple sugar derived from milk sugar.
Glucose— A simple sugar and the chief energy source in the body.
Lactase enzyme— The enzyme produced by cells that line the small intestine which allows the body to break down lactose.
Lactose— The primary sugar in milk.
Resources
ORGANIZATIONS
American Dietetic Association. (800) 366-1655. 〈http://www.eatright.org/nfs/nfs43.html〉.
OTHER
"Lactose Intolerance." Onebody.com. 〈http://www.onebody.com〉.
Lactose Intolerance
Lactose intolerance
Definition
Lactose intolerance is defined as the inability to digest the milk sugar, lactose, because of a deficiency of the digestive enzyme lactase.
Description
Lactose is the main sugar found in milk and other dairy products. Lactose is broken down by the enzyme lactase. Lactase is produced by cells in the inner lining of the small intestine. Lactase breaks down lactose into simpler forms (glucose and galactose) which can be more readily absorbed into the bloodstream. When lactase is insufficient, lactose cannot be digested and absorbed by the body. High concentrations of undigested lactose pull water into the small intestine which causes diarrhea . The unabsorbed lactose then moves into the large intestine where fermentation by bacteria results in excessive gas and acidic stool.
Demographics
Estimates indicate that between 25% of people in the United States and 75% of people worldwide experience lactose intolerance. The prevalence of lactose intolerance varies among ethnic groups. People from Northern Europe have a lower prevalence while lactose intolerance is common in Ashkenazi Jews (Jews from eastern France, Germany and Eastern Europe) and Asian, American Indian, black, and Hispanic adults. There is no difference in the incidence of lactose intolerance between males or females. Lactase enzyme activity corresponds to age and begins to decline around age 2 years. Symptoms of decreased enzyme activity do not usually become obvious until age 6-7 years but sometimes are not apparent until adulthood.
Causes and symptoms
There are three main types of lactose intolerance: primary, secondary, and congenital. The most common type is primary intolerance or adult-onset lactose intolerance. Adult-onset lactose intolerance is a normal part of aging for some people. Secondary lactose intolerance happens after illness (e.g. celiac disease , gastroenteritis, and inflammatory bowel disease), surgery, or injury to the small intestine. Secondary intolerance may last only a short time and may be reversible. Congenital intolerance occurs when an infant is born with lactose intolerance because both parents pass on a defective gene. Babies born with congenital intolerance cannot tolerate their mother's breast milk and experience diarrhea soon after birth.
Signs and symptoms of lactose intolerance usually occur 30 minutes to two hours after consuming foods that contain lactose. Symptoms are usually mild. The most common symptom is diarrhea. Other symptoms include nausea, abdominal cramps, bloating, and gas. The severity of symptoms differs from person to person and is dependent upon age, ethnic background, amount of lactose consumed, and the degree of lactose intolerance.
Diagnosis
Diagnosis may be made by obtaining a detailed history and dietary elimination of foods from the diet that are suspected of causing symptoms. Lactose intolerance can be presumed when symptoms resolve when suspect foods are eliminated from the diet and symptoms resume when these foods are reintroduced.
Other diagnostic tests for lactose intolerance include the lactose hydrogen breath test, the lactose tolerance test, and the stool acidity test. The lactose hydrogen breath test detects the amount of hydrogen in the breath. Hydrogen is not normally detectable in the breath but hydrogen is formed from undigested lactose by bacteria in the colon. Hydrogen formed in the colon is transported to the lungs then exhaled.
For the lactose tolerance test, a fasting blood glucose (sugar) level is drawn then blood samples are taken every two hours after ingestion of a dose of liquid that contains lactose. The lactase enzyme breaks down lactose into glucose and galactose then the liver metabolizes galactose into glucose. If lactose intolerance is present, the level of blood glucose does not increase because lactose in incompletely absorbed. A diagnosis of lactose intolerance can then be made.
The stool acidity test measures the amount of acid in the stool. Undigested lactose fermented by bacteria in the colon forms lactic acid that can be detected in the stool
Treatment
For primary lactose intolerance, the most apparent way to treat the condition is to decrease the amount of lactose in the diet. Most people with primary lactose intolerance are able to tolerate small and sometimes even moderate amounts of lactose. Consuming smaller amounts of dairy products more often may reduce symptoms. Consuming milk at mealtimes slows digestion so symptoms of lactose intolerance are decreased. For people with severe symptoms of primary lactose intolerance, dietary limitations may be more restrictive. The lactase enzyme is available over-the-counter (OTC) in caplet or tablet form to take with dairy products. Lactose tolerance may be improved by gradually introducing dairy foods into the diet.
For patients with secondary lactose intolerance, the underlying cause must be identified and treated. Special formulas are available for infants with congenital lactose intolerance.
Nutrition/Dietetic concerns
The chief dietary concern is for nutritional balance. In people with lactose intolerance, ensuring adequate intake of calcium and Vitamin D is essential. Dairy products provide adequate amounts of calcium and Vitamin D. Calcium is not absorbed when there is an inadequate amount of Vitamin D in the body. Inadequate calcium in the diet may lead to osteoporosis which is a condition in which bones become fragile and break easily.
In addition to dairy products, foods high in calcium include dark green vegetables (e.g. broccoli, Chinese cabbage, collard greens, kale, and turnip greens), salmon, and sardines. Although yogurt is somewhat high in lactose, it is high in calcium and is usually well tolerated by people with lactose intolerance. Lactose-reduced or lactose-free products are available at some supermarkets.
Many prepared food are high in lactose. These foods include bread and other baked goods, processed breakfast cereals, instant potatoes, soups, and breakfast drinks, margarine, lunch meats, salad dressings, candies and other snacks, and mixes for pancakes, biscuits, and cookies. Calcium supplements may be necessary for individuals who are intolerant of even small amounts of dairy products.
Therapy
Treat lactose intolerance with dietary changes, using lactase enzyme supplements, and adaptation to increasing amount of foods with lactose. Learn to identify which foods can be eaten without discomfort and which foods should be avoided. Consult a physician or dietitian to determine if calcium and Vitamin D supplements are needed.
Prognosis
Lactose intolerance is easy to manage and is not considered a dangerous condition.
Prevention
There is no known way to prevent lactose intolerance.
Caregiver concerns
Determine what level of lactose is tolerable. Experiment with a variety of dairy products. Ensure enough calcium and Vitamin D is consumed in the diet.
QUESTIONS TO ASK YOUR DOCTOR
- Is it necessary to avoid all dairy foods?
- What other treatments or tests do you recommend?
- Am I at risk of calcium deficiency?
- Will my lactose intolerance get worse?
Include foods beside dairy products that are high in calcium. Learn to read food labels to identify foods that contain the words milk or lactose. Other words on a food label such as whey, curds, milk by-products, dry milk solids, and non-fat dry milk powder also contain lactose. Keep anti-diarrhea medicine available to reduce or treat symptoms of lactose intolerance. Lactose intolerance is not the same as an allergy to milk. Proteins in milk are the cause of a milk allergy not lactase.
June G. Borazjani R.N., M.S.N., C.P.H.Q.
Lactose Intolerance
Lactose Intolerance
Who Becomes Lactose Intolerant?
How Is Lactose Intolerance Diagnosed?
Living with Lactose Intolerance
Lactose intolerance is the inability to digest lactose, the main sugar contained in milk products.
KEYWORDS
for searching the Internet and other reference sources
Galactose
Glucose
Lactase
Metabolism
Erin’s Story
Erin’s favorite food had been ice cream since her first birthday. On her thirteenth birthday, the rocky road sundae with hot fudge went down without a hitch, but an hour later she felt awful. She had cramps and diarrhea*, and, even more embarrassing, gas. Erin’s friend, whose mother had the same reaction to milk products, explained that she probably was becoming lactose intolerant, meaning that she could not digest all of the natural sugar in the ice cream.
- * diarrhea
- (dy-a-RE-a) is abnormally frequent and watery bowel movements.
What Is Lactose Intolerance?
Lactose intolerance refers to the inability of the small intestine to break down the sugar lactose (LAK-tos) because of a lack of or too little of the enzyme* lactase (LAK-tays). Lactose is a complex sugar found in milk products. Normally, when lactose reaches the small intestine, it is broken down into the simple sugars glucose (GLOO-kose) and galactose (ga-LAK-toz) by a protein, or enzyme, called lactase. Simple sugars can be absorbed easily through the wall of the small intestine into the bloodstream, but larger, more complex sugars like lactose cannot. If someone is lactose intolerant, that person’s intestine does not make enough lactase, or the lactase it does make does not work properly.
- * enzyme
- (EN-zim) is a natural substance that speeds up a specific chemical reaction in the body.
If lactose is not broken down, it absorbs water, so that the water cannot pass through the intestinal wall into the bloodstream. This extra fluid remaining in the bowel causes diarrhea. Also, bacteria (microorganisms) in the digestive tract convert lactose to lactic (LAK-tik) acid in a process called fermentation (fur-men-TAY-shun). Fermentation causes bowel movements to be acidic and burn, and it also causes gas, bloating, and cramps. Lactose intolerance is not dangerous, but it is uncomfortable.
Who Becomes Lactose Intolerant?
Doctors estimate that 30 to 50 million people in the United States are lactose intolerant. Up to 75 percent of people of African, Mexican, and Native American ancestry develop lactose intolerance, as do 90 percent of people of Asian ancestry. People of other ancestry are affected less by the problem.
Many people develop lactose intolerance as they get older, because the ability to make lactase decreases with aging. Digestive diseases and injuries to the small intestine also can cause lactose intolerance. Occasionally, children are born without the ability to make lactase.
Nondairy Sources of Lactose
Milk, cheese, butter, and ice cream are obvious sources of lactose, but did you know that lactose often is added to the following items?
- Baked goods, including bread, and mixes for baked goods
- Instant breakfast drinks, potatoes, and soups
- Lunch meats
- Margarine
- Nonfat dry milk powder
- Powdered coffee creamer
- Many prescription drugs
- Processed breakfast cereal
- Salad dressing
- Many snack foods
- Whey
- Whipped toppings
How Is Lactose Intolerance Diagnosed?
Doctors use three tests to diagnose lactose intolerance. After a person eats or drinks something containing lactose, the doctor can:
- Test for a low level of glucose in the bloodstream, which would show that lactose was not broken down properly and absorbed (lactose intolerance test)
- Test for a lot of hydrogen in exhaled breath, a sign that bacteria are fermenting lactose (hydrogen breath test)
- Test for acidic bowel movements, also a sign that fermentation is occurring (stool acidity test); usually used to test infants and small children
Living with Lactose Intolerance
Symptoms vary from person to person and depend on the amount of lactose eaten. Trial and error helps people learn what not to eat or how much they can eat without becoming ill. Avoiding milk products should eliminate symptoms of lactose intolerance, but people on such a diet must get calcium and vitamin D from other sources. Nonprescription products containing lactase are available that can be taken along with milk products and help the body break down lactose.
Lactose intolerance usually can be managed by following simple strategies:
- Drink milk in small servings: 1 cup or less per serving.
- Eat cheeses that are low in lactose, such as cheddar.
- Only drink milk with meals or other foods.
- Eat active-culture yogurts, which contain less lactose than other dairy products.
- Use low-lactose or lactose-free milk.
- Take lactase enzyme tablets before consuming dairy products, or add lactase enzyme drops to regular milk.
See also
Diarrhea
Metabolic Disease
Lactose Intolerance
Lactose Intolerance
Lactose intolerance is the inability to digest significant amounts of lactose, the primary sugar in 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 lactose into simpler forms that can then be absorbed into the bloodstream during the digestive process. Common symptoms of lactose intolerance include nausea , cramps, bloating, gas, and diarrhea.
Structure and Functions of Lactose
Lactose is a disaccharide carbohydrate , composed of the two monosaccharides, glucose and galactose. When lactose reaches the digestive system, the lactase enzyme breaks down lactose into glucose and galactose. The liver then changes the galactose into glucose. If this process occurs normally, the glucose enters the bloodstream and raises the blood glucose level.
Prevalence
As many as 75 percent of all adults worldwide are lactose intolerant, and between 30 million and 50 million Americans are lactose intolerant. Certain racial or ethnic groups are more widely affected than others. As many as 75 percent of all African-American, Jewish, Native American, and Mexican-American adults, and 90 percent of Asian-American adults are lactose intolerant. The condition is least common among persons of northern European descent.
Types of Lactose Intolerance
There are three basic types of lactose intolerance: primary, secondary, and congenital . In primary lactose intolerance, the body begins to produce less lactase after about the age of two, depending on an individual's racial or ethnic background. This type is genetically determined and is a permanent condition.
Secondary lactose intolerance, on the other hand, is temporary and results from a disease or medications that damage the lining of the small intestine where lactase is normally active. Secondary lactose intolerance gradually disappears when the illness passes.
Congenital lactose intolerance is an extremely rare condition in which the lactase enzyme is completely absent at birth. Unlike other types of lactose intolerance, this type requires complete avoidance of lactose.
Clinical Diagnosis
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.
The lactose tolerance test involves an individual drinking a liquid that contains lactose. The individual must fast before this test, in which several blood samples are taken over a two-hour period to measure the blood glucose level, which indicates how well the body is able to digest lactose. If lactose is incompletely absorbed, then the blood glucose level will not rise, confirming a diagnosis of lactose intolerance.
The hydrogen breath test measures the amount of hydrogen in the breath. Normally, no 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. As with the previous test, a lactose-loaded beverage is consumed, and the individual then breathes into a machine that measures the amount of hydrogen in the breath.
The stool acidity test measures the amount of acid in a person's stool. 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.
Nutrition for People with Lactose Intolerance
There are degrees of intolerance for lactose. Studies have shown that many true lactose intolerants can consume moderate amounts of milk and dairy products without symptoms, particularly if milk is part of a meal.
Milk and other dairy products are a major source of calcium . Many people with lactose intolerance may be able to tolerate yogurt with active cultures, which is very high in calcium, 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. Lactose-intolerant individuals should also be able to tolerate cheese, as most of the lactose is removed, along with the whey, when the cheese is made.
However, people with lactose intolerance who do not drink milk or eat diary products can still get the calcium they need from dark-green, leafy vegetables such as broccoli, turnip or collard greens, and kale. Certain fish with soft, edible bones, such as herring, salmon, or sardines, are also good calcium sources.
Although milk and foods made from milk are the only natural sources, lactose is often added to processed foods , such as bread, cereal, and salad dressing. This is because dairy products can contribute to the required or desired flavor, color, and texture of many foods, in addition to increasing the nutritional value of processed foods. Some products that are labeled "nondairy," such as powdered coffee creamer and whipped toppings, may include ingredients that are derived from milk, and therefore contain lactose. It is important to carefully read food labels, looking not only for milk and lactose among the contents, but also for such terms as whey, curds, milk by-products, dry milk solids, and nonfat dry milk powder, all of which contain lactose.
see also African Americans, Diet of; Africans, Diets of; Asians, Diet of; Carbohydrates.
Gita C. Gidwani
Bibliography
National Digestive Diseases Information Clearinghouse (2002). "Lactose Intolerance." NIH Publication No. 02-2751. Available from <http://www.niddk.nih.gov>