How the BodyUses Food:

Digestion andAbsorption

Nutrition Scoreboard

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1 Almost all of the carbohydrate and fat you consumein foods is absorbed by the body, but only about halfof the protein is.

2 Disorders of the digestive system are a leading causeof hospitalizations and medical visits in the UnitedStates and Canada.

3 Lactose maldigestion is a common digestive disorder.

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[ KEY CONCEPTS AND FACTS ]

• Our bodies are in a continu-ous state of renewal. Mate-rials used to renew bodytissues come from the foodwe eat in the form of nutrients.

• Digestion and absorption areprocesses that make nutri-

ents in foods available foruse by the body.

• Digestive disorders arecommon and often relatedto dietary intake.

Answers to Nutrition Scoreboard

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1 Over 90% of all the carbohydrates, fats, and proteinsconsumed in food are absorbed and become part ofthe body.

2 Digestive disorders are the leading cause of hospi-talizations among 20- to 44-year-olds in the UnitedStates and Canada. They account for over 70 millionmedical visits in the United States each year.1

3 Over half of the world’s population digests lactosefrom milk and milk products incompletely or not at all.2

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My Body, My Food

La vie est une fonction chimique. (“Life is a chemical process.”)—Antoine Lavoisier, late eighteenth century

You are not the same person you were a month ago. Although your body looks thesame and you don’t notice the change, the substances that make up the organs andtissues of your body are constantly changing. Tissues we generally think of as solidand permanent, such as bones, the heart and blood vessels, and nerves, are contin-ually renewing themselves. The raw materials used in the body’s renewal processesare the nutrients you consume in foods.

Each day, about 5% of our body weight is replaced by new tissue. Existing com-ponents of cells are renewed, the substances in our blood are replaced, and body flu-ids are recycled. Taste cells, for example, are replaced about every 7 days, and cellslining the intestinal tract every 1 to 3 days. All of the cells of the skin are replacedevery month. Red blood cells turn over every 120 days. If you thought it was hardto maintain a car, an apartment, or a house, just imagine what the maintenance ison a body! Maintenance is just one of the body’s ongoing functions that requirenutrients as raw material.

How Do Nutrients in Food Become Available for the Body’s Use?

The human body is an amazing machine. Mine is, anyway. For example, Iregularly feed my body truly absurd foods, such as cheez doodles, and somehow it

turns them into useful body parts, such as glands. At least I assume it turns theminto useful body parts.3

—Dave Barry, 1987

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The components of food that make “useful body parts” are nutrients. Through theprocesses of digestion and absorption, they are made available for use by every cellin the body.

The Internal Travels of Food: An Overview] The “food processor” of the bodyis the digestive system shown in Illustration 7.1. It consists of a 25- to 30-foot-long

Illustration 7.1The digestive system.

Salivary glands• produce enzymesthat help break down starch and fats

Tongue• mastication and mixing of food with saliva

Esophagus• transfers food tothe stomach

Large intestine(colon)• site of absorptionof water

• site of mostintestinal bacteria

Stomach• secretes enzymes that break down proteins and fats

• mixes and liquifies food

Rectum• stores waste products forelimination

Small intestine• secretes enzymes thatbreak down carbohydrates,proteins, and fats

• site of nutrient absorption

Pancreas• secretes enzymes that break down carbohydrates,proteins, and fats

Liver• produces bile thataids fat digestion

Oral cavity

Pancreatic duct• conducts pancreatic juiceinto small intestine

Bile duct• conducts bile tosmall intestine

Anus• holds rectum closed

• opens to allow elimination

Gallbladder• stores and secretes bilethat aids in fat digestion

Index Stock

digestionThe mechanical and chemicalprocesses whereby ingestedfood is converted into sub-stances that can be absorbedby the intestinal tract and uti-lized by the body.

absorptionThe process by which nutrientsand other substances aretransferred from the digestivesystem into body fluids fortransport throughout the body.

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monosaccharides(mono � one, saccharide �sugar) Simple sugars consist-ing of one sugar molecule.Glucose, fructose, and galac-tose are monosaccharides.

enzymesProtein substances that speedup chemical reactions.Enzymes are found throughoutthe body but are present inparticularly large amounts inthe digestive system.

starch Complex carbohydrates madeup of complex chains of glu-cose molecules. Starch is theprimary storage form of carbo-hydrate in plants. The vastmajority of carbohydrate inour diet consists of starch,monosaccharides, and disaccharides.

disaccharideSimple sugars con-sisting of two sugarmolecules. Sucrose(table sugar) consistsof a glucose and afructose molecule,lactose (milk sugar)consists of glucoseand galactose, andmaltose (malt sugar)consists of two glu-cose molecules.

bileA yellowish-brownor green fluid pro-duced by the liver,stored in the gall-bladder, andsecreted into thesmall intestine. Itacts like a deter-gent, breaking downglobs of fat enteringthe small intestineto droplets, makingthe fats more acces-sible to the actionof lipase.

muscular tube and organs such as the liver and pancreas that secrete digestive juices.The digestive juices break foods down into very small particles that can be absorbedand used by the body. The absorbable forms of carbohydrates are monosaccharides,such as glucose and fructose. Proteins are absorbed as amino acids, and fats as fattyacids and glycerol. Vitamins and minerals are not broken down before they areabsorbed; they are simply released from foods during digestion.

Much of the work of digestion is accomplished by enzymes manufactured bycomponents of the digestive system such as the salivary glands, stomach, and pan-creas. Enzymes are complex protein substances that speed up reactions that breakdown food. A remarkable feature of enzymes is that they are not changed by thechemical reactions they affect. This makes them reusable.

Carbohydrates, proteins, and fat each have their own set of digestive enzymes.All together, over a hundred different enzymes participate in the digestion of carbo-hydrates, proteins, and fat. Table 7.1 presents information on some of the enzymesinvolved in digestion and highlights their specific roles. In Table 7.2 you will seethese enzymes cited in the summary of the processes involved in the digestion ofcarbohydrate, fat, and protein.

A Closer Look] As you chew food, glands under the tongue release saliva thatlubricates food so that it can be swallowed and pass easily along the intestinal tract.Saliva also gets food digestion started. It contains salivary amylase and lipase thatbegin to break down carbohydrates and fats.

TABLE 7.1

PRIMARY FUNCTION OF SOME DIGESTIVE ENZYMES.

ENZYME ENZYME FUNCTION ENZYME SOURCE

A. Carbohydrate DigestionAmylase Breaks down into smaller Produced in the salivary glands

chains of glucose molecules (salivary amylase) and the pancreas (pancreatic amylase)

Sucrase Separates the sucrose Produced in the small intestineinto glucose and fructose

Lactase Splits the disaccharide lactose into Produced in the small intestineglucose and galactose

Maltase Separates maltose into two Produced in the small intestinemolecules of glucose

B. Fat DigestionLipase Breaks down fats into fragments Produced in salivary glands

of fatty acids and glycerol (lingual lipase), and the pancreas (pancreatic lipase). The action of lipase is enhanced by bile

C. Protein DigestionPepsin Separates protein into shorter Produced by the stomach

chains of amino acids

Trypsin Splits short chains of amino acids Produced by the pancreasinto molecules containing, one, two or three amino acids

disaccharide

starch

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After food is chewed, it is swallowed and passes down the esopha-gus to the stomach. Muscles that act as valves at the entrance and exitof the stomach ensure that the food stays there until it’s liquified, mixedwith digestive juices, and ready for the digestive processes of the smallintestine. Solid foods tend to stay in the stomach for over an hour,whereas most liquids pass through it in about 20 minutes. When thestomach has finished its work, it ejects 1 to 2 teaspoons of its liquifiedcontents into the small intestine through the muscular valve at its end.Stomach contents continue to be ejected in this fashion until they aretotally released into the small intestine. These small pulses of liquifiedfood stimulate muscles in the intestinal walls to contract and relax; thesemovements churn and mix the food as it is digested by enzymes. Whenthe diet contains a lot of fiber and sufficient fluids, the bulge of digest-ing food in the intestine tends to be larger. Larger food bulges stimulate a higherlevel of intestinal muscle activity than do smaller food bulges. Thus, high-fiber mealspass through the digestive system somewhat faster than low-fiber meals.

TABLE 7.2

SUMMARY OF THE DIGESTION OF CARBOHYDRATES, FATS, AND PROTEINS.

MOUTH STOMACH

Carbohydrates(excluding fiber)

Fiber

Fat

Protein

The salivary glandssecrete saliva to mois-ten and lubricate food;chewing crushes andmixes it with salivaryamylase that initiatesstarch digestion.

The teeth crush fiberand mix it with salivato moisten it for swallowing.

Fat-rich foods aremixed with saliva. Smallamounts of linguallipase accomplish somefat breakdown.

In the mouth, chewingcrushes and softensprotein-rich foods andmixes them with saliva.

Digestion of starchcontinues while foodremains in the stomach.Some alcohol (a carbohydrate-like sub-stance) is absorbed.Acid produced in thestomach aids digestion and destroys bacteria in food.

No action.

Fat tends to separatefrom the watery stom-ach fluid and foods andfloat on top of themixture. Only a smallamount of fat isdigested. Fat is last toleave the stomach.

Stomach acid works touncoil protein strandsand to activate thestomach’s protein-digesting enzyme.Pepsin breaks the pro-tein strands intosmaller fragments.

Pancreatic amylasecontinues starch diges-tion. Sucrase, lactase,and maltase breakdown disaccharides into monosaccharides.Some alcohol isabsorbed here.

Fiber binds cholesteroland some minerals.

Bile readies fat for theaction of lipase fromthe pancreas. Lipasesplits fats into fattyacids and glycerolfragments.

Trypsin splits proteininto molecules contain-ing one, two, or threeamino acids.

Undigested carbohy-drates reach the colonand are partly brokendown by intestinal bacteria.

Most fiber is excretedwith feces; some fiberis digested by bacteriain the colon.

A small amount of fattymaterials escapesabsorption and is car-ried out of the bodywith other wastes.

The large intestine car-ries undigested proteinresidue out of the body.Normally, almost allfood protein is digestedand absorbed.

SMALL INTESTINE,PANCREAS,

LIVER, AND GALLBLADDER

LARGE INTESTINE(COLON)

Get Your Juices FlowingYou don’t have to actually eat food tostart your digestive juices flowing. Youjust have to think about food or see it.4

Put this information to the test. Clearyour mind, turn the page, and take aclose look at Illustration 7.2.

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Digestion, as well as the absorption of nutrients, is greatly enhanced by thestructure of the intestines (Illustration 7.3). Fingerlike projections called “villi” linethe inside of the intestinal wall and increase its surface area tremendously. If laidflat, the surface area of the small intestine would be about the size of a baseballinfield, or approximately 675 square feet. This large mass of tissue requires a highlevel of nutrients for maintenance. Much of this need (50% in the small intestineand 80% in the large intestine) is met by foods that are being digested.5

Digestion is completed when carbohydrates, proteins, and fats are reduced tosubstances that can be absorbed, and when vitamins and minerals are released fromfood. Most nutrients are absorbed in the small intestine. Water, sodium, and someof the end products of bacterial digestion, however, are absorbed from the largeintestine. The large intestine is home to many strains of bacteria that consume undi-gested fiber and other types of complex carbohydrates that are not broken down byhuman digestive enzymes. These bacteria excrete gas as well as fatty acids that arepartly absorbed in the large intestine. Substances in food that cannot be absorbedcollect in the large intestine and are excreted in the stools.

Absorption] Absorption is the process by which the end products of digestionare taken up by the lymphatic system (Illustration 7.4) and the circulatory system(Illustration 7.5) for eventual distribution to cells of the body. Lymph vessels and

Illustration 7.3Scanning electron micro-graphs of cross sections ofthe small intestine (left) andthe large intestine (right). Note the high density of villi inthe small intestine and the relative flatness of the lining of the large intestine.

Illustration 7.2Testing, testing. This is a testof your salivary secretions.Did the lemon speak directlyto your salivary glands?

If you want to turn thedigestive processes off, quitthinking about food. Finishyour reading assignment!

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lymphatic systemA network of vessels thatabsorb some of the products ofdigestion and transport themto the heart, where they aremixed with the substancescontained in blood.

circulatory systemThe heart, arteries, capillaries,and veins responsible for cir-culating blood throughout the body.

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blood vessels infiltrate the villi that line the inside of the intestines (Illustration 7.6)and transport absorbed nutrients toward the major branches of the lymphatic andcirculatory systems. The breakdown products of fat digestion are largely absorbedinto lymph vessels, whereas carbohydrate and protein breakdown products enterthe blood vessels.

The nutrient-rich contents of the lymphatic system are transferred to the blood-stream at a site near the heart where vessels from both systems merge into one ves-sel. From there the lymph and blood mixture is sent to the heart and subsequentlythroughout the body by way of the circulatory system. The circulatory systemreaches every organ and tissue in the body, thereby supplying cells with nutrientsobtained from food.

TonsilsLymphnode

Thymus

Spleen

Lymphvessels

Ar teries

Hear t

Veins

McMahon

Illustration 7.4(left) The lymphatic system.

Illustration 7.5(right) The circulatory systemincludes the heart and bloodvessels. This system serves as the nutri-ent transportation system ofthe body.

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Beyond Absorption} Cells can use nutrients directly for energy, body structures, orthe regulation of body processes, or convert them into other usable substances. Forexample, glucose delivered to cells can be used “as is” for energy formation or con-verted to glycogen and stored for later use. Fatty acids, an end product of fat diges-tion, can be incorporated into cell membranes or used in the synthesis of certainhormones. Vitamins and minerals freed from food by digestion can be used by cellsto control enzyme activity or can be stored for later use. The body has a limited stor-age capacity for some vitamins and minerals. Consequently, excessive amounts ofcertain vitamins and minerals such as vitamin C, thiamin, and sodium are largelyexcreted in urine.

Digestion and Absorption Are Efficient} Of our intake of energy nutrients, approx-imately 99% of the carbohydrate, 92% of the protein, and 95% of the fat we con-sume in food are digested and absorbed. Dietary fiber, however, leaves the digestivesystem in much the same form as it entered. Humans don’t have enzymes that breakdown fiber. It should be noted, however, that some fiber is digested in the large intes-tine by bacteria.

Digestive Disorders Are CommonExcluding childbirth, digestive disorders such as heartburn, hemorrhoids, irritablebowel syndrome, and duodenal and stomach ulcers are the leading cause of hospi-talization among U.S. and Canadian adults aged 20–44 years. They account for over70 million medical visits yearly in the United States alone.6 Table 7.3 shows the per-centages of U.S. adults who have common digestive disorders. Digestive disordersare common in children as well as adults. At least one-third of U.S. adults experi-ence heartburn, and up to 28% of school children experience constipation.8

Constipation and Hemorrhoids] Both constipation and hemorrhoids are oftendue to diets that provide too little fiber. Fiber intakes by adults of 25 to 30 gramsper day along with plenty of fluids (8 to 12 cups a day) can help prevent constipa-

heartburnA condition that results whenacidic stomach contents arereleased into the esophagus,usually causing a burning sensation.

hemorrhoids (hem-or-oids)Swelling of veins in the anusor rectum.

irritable bowel syndrome(IBS)A disorder of bowel functioncharacterized by chronic orepisodic gas, abdominal pain,diarrhea or constipation, orboth.

duodenal (do-odd-en-all)and stomach ulcersOpen sores in the lining of theduodenum (the uppermost partof the small intestine) or thestomach.

lllustration 7.6Structure of villi, showingblood and lymph vessels.

Capillary network

Lymph vessel

Outermost layer of cells

ArteryVein

Lymph vessel

Muscletissue

Villi

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tion and hemorrhoids in healthy people. Some good sources of dietary fiber areshown in Illustration 7.7.

Ulcers and Heartburn] Ulcers develop when the protective barrier formed bycells lining the stomach and duodenum (the uppermost part of the small intestine)is damaged. This allows stomach acid and digestive enzymes to erode the lining ofthe stomach and duodenum and cause an “ulcer.” Duodenal ulcers are ten timesmore common than stomach ulcers and are closely associated with the presence ofHelicobacter pylori (H. pylori) bacteria.9 H. pylori infects and irritates the lining ofthe stomach. The infection is acquired by the ingestion of foods and other sub-stances contaminated with saliva, vomit, or feces from people harboring the bacte-ria in their stomach. Rates of H. pylori infection are highest in countries with poorsanitary conditions.10 Excessive production of stomach acid can lead to ulcers, too,and may also cause heartburn. Heartburn is unrelated to heart conditions. It iscalled that because acid that escapes from the stomach causes a burning sensationin an area of the esophagus located near the heart.

Stress, anxiety, and frequent use of aspirin, ibuprofen, naproxen, and othermedications appear to be related to the development of ulcers and heartburn insome people.11 Fatty foods, coffee, alcohol, citrus fruits, soft drinks, and a varietyof other foods have been implicated in the development of ulcers and heartburn.Rather than cause these disorders, certain foods appear to aggravate the symptomsof ulcers and heartburn. High-fiber diets, on the other hand, appear to be protectiveagainst the development of ulcers and heartburn.12

A number of medications are available for the treatment of H. pylori and theexcessive production of stomach acid. Reduction of stress, judicious elimination ofoffending foods and beverages from the diet, and small, frequent meals also helprelieve ulcers and heartburn in some people.13

Irritable Bowel Syndrome] Irritable bowel syndrome, abbreviated IBS, is notconsidered a disease but rather a persistent disorder in the way the colon functions.For some reason, the colon (or bowel) in people with IBS spasms, and that leads to

TABLE 7.3

COMMON DIGESTIVEDISORDERS.7

U.S. ADULTS AFFECTED*

Heartburn 33.0%

Hemorrhoids 12.8

Irritable bowel syndrome 6–12%

Ulcers 3.5

Chronic constipation 3.0

Chronic diarrhea 1.2

*Noninstitutionalized adults experi-encing the disorder in the past 12months.

All Bran Cereal, 1/3 c. (10 g)

1 mango (4 g)

1 pear with skin (4 g)

1/2 c. lima beans (5 g)

1/2 c. corn (3 g)1/2 c. carrots (2.8 g)

lllustration 7.7Food sources of dietary fiber.Together, the foods shown pro-vide 29 grams of dietary fiber,an amount that helps preventconstipation.

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painful cramps. Gas production, a feeling of being bloated, diarrhea, constipation,or both, are common features of IBS. Most commonly, mild IBS is treated with alow-fat diet (25% of calories), counseling, and over-the-counter fiber powders,antidiarrhea pills, and pain medications. More serious cases may respond to stressreduction, eating in relaxed surroundings, antidepressants, and drugs that reducecolon muscle spasms. Probiotics, or “friendly” bacteria that help colonize the colonwith microorganisms that help protect and heal the colon lining, are being increas-ingly used for this disorder.14

Diarrhea] Diarrhea is a common problem in the United States and a leading pub-lic health problem in developing countries. Most cases of diarrhea are due to bacte-rial- or viral-contaminated food or water, lack of immunizations against infectiousdiseases, and vitamin A, zinc, and other nutrient deficiencies that make children par-ticularly susceptible to diarrhea. Diarrhea can deplete the body of fluid and nutri-ents and produce malnutrition as well. If it lasts more than two weeks or is severe,diarrhea can lead to dehydration, heart and kidney malfunction, and death. An esti-mated 3.5 million deaths from diarrhea diseases occur each year to the world’s pop-ulation of children 5 years of age or under.15

The vast majority of cases of diarrhea can be prevented through food and watersanitation programs, immunizations, and adequate diets. The early use of oral rehy-dration fluids (for example, the formula provided by the World Health Organiza-tion and commercial formulas such as Pedialyte and Rehydralyte) shortens theduration of diarrhea. Rehydration generally takes 4 to 6 hours after the fluids arebegun.16

Rather than “resting the gut” during diarrhea as used to be recommended, chil-dren and adults, once rehydrated, should eat solid foods. Foods such as yogurt, lactose-free or regular milk, chicken, potatoes and other vegetables, dried beans,and rice and other cereals are generally well tolerated and provide nutrients neededfor the repair of the intestinal tract. It is best to avoid sugary fluids such as softdrinks. High-sugar beverages tend to draw fluid into the intestinal tract rather thanincrease the absorption of fluid.17

Flatulence] Everyone experiences flatulence—it’s normal. Gas can occur in theesophagus, stomach, small intestine, and large intestine due to swallowed air or bac-terial breakdown of food in the large intestine. Air may be swallowed along withfood and beverages or while chewing gum. Eating and drinking while in a rush gen-erally increases air ingestion. Bacterial production of gas in the large intestine may

be related to the ingestion of dried beans, broccoli, cauliflower, brusselssprouts, onions, corn, and other vegetables containing a type of complexcarbohydrate that bacteria, but not humans, can break down. Fructose,which is used to sweeten a variety of food products and beverages, andsorbitol (used in some types of candy and gum) may lead to gas forma-tion by bacteria that produce gas as a waste product of carbohydratedigestion. Heartburn and other gastrointestinal tract disorders and med-ications such as antibiotics are also associated with gas production.18

People often think they produce too much gas, even when they don’t.The amount of gas swallowed and produced by gut bacteria varies agood deal among individuals, and within the same individual. Gas pro-duction changes depending on what foods are eaten, the types of bacte-ria populating the large intestine, the medications used, and the presenceof gastrointestinal tract disorders. Severe and painful symptoms relatedto gas production may signal the presence of a digestive disorder.19

probioticsNon-harmful bacteria andsome yeasts that help colonizethe intestinal tract with bene-ficial microorganisms and thatsometimes replace colonies ofharmful microorganisms. Mostcommon probiotic strains areLactobacilli and Bifidobacteria.

diarrheaThe presence of three or moreliquid stools in a 24-hourperiod.

flatulence (flat-u-lens)Presence of excess gas in thestomach and intestines.

Ancient Perspectives on Flatulence

Passing gas isnecessary to well-being.

—Hippocrates

All Roman citizensshall be allowed topass gas whenevernecessary.

—Claudius

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Stomach Growling] Gas in the stomach can make your stomach growl. Whenyour stomach growls, you know that gas and food or fluids are mixing in yourstomach. The growling tends to be louder when your stomach is empty, whenthere’s no food to muffle the noise. It can occur anytime, whether your stomach isempty or full, but is more likely to happen when your stomach is empty.20

Lactose Maldigestion and Intolerance

I can’t drink milk. It tears me up inside.

A very common digestive disorder is lactose maldigestion. The lactose found in milkand milk products presents a problem for most of the world’s adults, who cannotdigest it, either partially or completely (Table 7.4).21 The condition occurs morecommonly in population groups that have no historical links to dairy farming andmilk drinking.23 Early humans in central and northwestern Europe and the regionsof Africa and China highlighted in Illustration 7.8 tended to raise dairy animals anddrink milk.

Lactose maldigestion is caused by a genetically determined low production oflactase, the enzyme that digests lactose. People who lack this enzyme end up withfree lactose in their large intestine after they consume milk or milk products thatcontain lactose. The presence of lactose in the large intestine produces the symptomsof lactose intolerance. These symptoms include a bloated feeling and diarrhea dueto fluid accumulation, and gas and abdominal cramping caused by the excretion ofgas by bacteria that digest lactose.

Illustration 7.8Lactose maldigestion is less common among descendants of people who consumed milkfrom domesticated animals during prehistoric times (light areas) than among peoplewhose early ancestors did not drink milk (dark areas).24

TABLE 7.4

ESTIMATED INCIDENCE OFLACTOSE MALDIGESTIONAMONG OLDER CHILDRENAND ADULTS INDIFFERENT POPULATIONGROUPS.22

INCIDENCE OF LACTOSEMALDIGESTION

Asian Americans 90%

Africans 70

African Americans 70

Asians 65 or more

American Indians 62 or more

Mexican Americans 53 or more

U.S. adults (overall) 25

Northern Europeans 20

American Caucasians 15

Lactose digestion

Lactose maldigestion

lactose maldigestionA disorder characterized byreduced digestion of lactosedue to the low availability ofthe enzyme lactase.

lactose intoleranceThe term for gastrointestinalsymptoms (flatulence, bloat-ing, abdominal pain, diarrhea,and “rumbling in the bowel”)resulting from the consump-tion of more lactose than canbe digested with available lactase.

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Lactose maldigestion is rare in young children and affects adults to variousdegrees. Some adults produce little or no lactase and develop symptoms of lactoseintolerance when they consume only small amounts of milk or milk products. Oth-ers produce some lactase and can tolerate limited amounts of lactose-containingmilk and milk products, such as a cup of milk at a time or two cups of milk

consumed with meals during the day. Regular consumption of milk mayimprove lactose digestion due to enhanced bacterial breakdown of lac-tose in the gut.25

Many people who are lactose maldigesters have no trouble eatingyogurt and other fermented milk products such as cultured buttermilk,kefir, and aged cheese. The bacteria used to culture yogurt can digesthalf or more of the lactose. This reduction in lactose content is sufficientto prevent adverse effects in many people with lactose maldigestion.26

Milk solids, milk, and other lactose-containing components of milkmay be added to foods you wouldn’t expect. Consequently, it’s best toexamine food ingredient labels when in doubt. Milk, for instance, is aprimary ingredient in some types of sherbet, and milk solids are addedto many types of candy.

Do You Have Lactose Maldigestion?] The single most reliable indi-cator of lactose maldigestion is the occurrence of lactose intolerancewithin hours after consuming lactose.27 If you consistently experiencethese symptoms (described earlier), visit your health care provider for adiagnosis. The symptoms could be due to lactose, other substances inmilk, or another problem.

How Is Lactose Maldigestion Managed?] Lactosemaldigestion should not be managed by omitting milk andmilk products from the diet! Doing so would exclude afood group that contributes a variety of nutrients that can-not easily be replaced by other foods. The omission of milkand milk products from the diet of people with lactoseintolerance promotes the development of osteoporosis.28

Rather, fortified soy milk, low-lactose cow’s milk, milk pre-treated with lactase drops, and yogurt and other fermentedmilk products (if tolerated) should be consumed. Illustra-tion 7.9 shows a variety of dairy products that are gener-ally well tolerated by people with lactose maldigestion.

Lactase tablets are also available and should be takenwithin 30 minutes of consuming lactose.29 Lactase is anenzyme, and enzymes are made of protein. Protein is par-tially digested in the stomach, so some of the lactaseingested in the tablets may not reach the small intestinewhere it is needed if the tablets are taken too far in advanceof eating.

Digestion is a remarkably complex and efficient processthat could be covered in much more detail than has been pre-sented here. Readers are encouraged to consult the Web siteslisted at the end of the unit for additional information.

Illustration 7.9Dairy products generally well tolerated by people withlactose maldigestion.

“Brain freeze,” or that splittingheadache you can get from eating icecream too fast, is caused by the quickdrop in temperature in the back ofyour mouth. That causes vessels toconstrict, and the result is an “icecream headache.”

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Key Termsabsorption, page 7–3

bile, page 7–4

circulatory system, page 7–6

diarrhea, page 7–10

digestion, page 7–3

disaccharide, page 7–4

duodenal and stomach ulcers,

page 7–8

enzymes, page 7–4

flatulence, page 7–10

heartburn, page 7–8

hemorrhoids, page 7–8

irritable bowel syndrome (IBS),

page 7–8

lactose intolerance, page 7–11

lactose maldigestion, page 7–11

lymphatic system, page 7–6

monosaccharides, page 7–4

probiotics, page 7–10

starch, page 7–4

www linkswww.healthfinder.govSearch digestive diseases by name, orsearch “digestion.”

www.navigator.tufts.eduNutrition Navigator will help you find themost reliable sites on topics related todigestion.

digestive.niddk.nih.govNIH’s National Digestive Disease Clearing-house homepage. This site provides links toinformation about specific digestive dis-eases, clinical trials, statistics, and answersto questions such as Why do I have gas?

www.nlm.nih.gov/medlineplusFind out more about digestion, absorption,organs of the gastrointestinal tract, anddigestive diseases at this site.

Notes1. Digestive disease statistics, National

Digestive Disease Clearinghouse,http://digestive.niddk.nih.gov/statistics/statistics.htm, accessed 8/03; and Lead-ing causes of hospitalization in Canada.Health Canada, Population and PublicHealth Branch, www.hc-sc.gc.ca,accessed 8/03.

2. Hertzler SR, Clancy SM. Kefir improveslactose digestion and tolerance in adultswith lactose maldigestion. J Am DietAssoc 2003; 103:582–74.

3. Leading causes of hospitalization inCanada (www.hc-sc.gc.ca).

4. Schneeman B. Nutrition and gastroin-testinal function. Nutr Today 1993;Jan/Feb:20–24.

5. Bengmark S. Econutrition and healthmaintenance: a new concept to preventGI inflammation, ulceration, and sepsis.Clin Nutr 1996;15:1–10.

6. Digestive disease statistics (http://digestive.niddk.nih.gov/statistics/statistics.htm); Leading causes of hospi-talization in Canada (www.hc-sc.gc.ca).

7. Digestive disease statistics (http://digestive.niddk.nih.gov/statistics/statistics.htm); Leading causes of hospi-talization in Canada (www.hc-sc.gc.ca).

8. Borowitz SM et. al. Precipitants of con-stipation during early childhood. J AmFam Pract 2003;16:213–8.

9. Current medical diagnosis and treat-ment, 35th ed. Stamford (CT): Appleton& Lange; 1997.

10. Suerbaum S, Michetti P. Helicobacterpylori infection. N Engl J Med 2002;347:1175–86.

11. Kurata AN, et al. Dyspepsia in primarycare: perceived causes, reasons forimprovement, and satisfaction with care.J Fam Practice 1997;44:281–8.

12. The Merck manual of medical informa-tion. Whitehouse (NJ): Merck ResearchLaboratory; 2000; and Suerbaum andMichetti, Helicobacter pylori infection.

13. Kurata et al., Dyspepsia in primary care.

14. Irritable bowel syndrome. AmericanGastroenterologial Association MedicalPosition Statement. Gastoenterol 1997;112:2118–9; and Barclay L. Highlightsfrom digestive diseases week. An expertinterview with Lawrence R. Schiller.Medscape Medical News, 2003,www.medscape.com.

15. Kilgore PE, et al. Trends in diarrhealdisease associated mortality in US chil-dren, 1968 through 1991. JAMA 1995;274:1143–8.

16. Kilgore et al., Trends in diarrheal dis-ease; Goepp JG, Katz SA, Oral rehydra-tion therapy, Am Fam Phys 1993;47:843–8; and Meyers A. Oral rehydration

therapy: what are we waiting for? AmFam Phys 1993;47:740–2.

17. Lima AAM, Guerrant RL. Persistentdiarrhea in children: epidemiology, riskfactors, pathophysiology, nutritionalimpact, and management. EpidemiolRev 1992;34:222–42; and Goepp andKatz, Oral rehydration therapy.

18. Digestive disease statistics (http://digestive.niddk.nih.gov/statistics/statistics.htm).

19. Digestive disease statistics (http://digestive.niddk.nih.gov/statistics/statistics.htm.

20. Stomach growling. Scientific American.Com ask the expert. www.scientificamerican.com, accessed 8/03.

21. Hertzler and Clancy, Kefir improves lac-tose digestion.

22. Scrimshaw NS, Murray, EB. Prevalenceof lactose maldigestion. Am J Clin Nutr1988;48(suppl):1086–98; and Inman-Felton AE. Overview of lactosemaldigestion (lactose nonpersistence). J Am Diet Assoc 1999;99:481–9.

23. Simmons FJ. Primary adult lactose intol-erance and the milking habit: a problemin biological and cultural interrelation-ships. I. Review of the medical research.Am J Digestion 1981;14:819.

24. Simoons FJ. Primary lactose intolerance

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and the milking habit: a problem inbiological and cultural interrelation-ships. Am J Digestive Diseases1970;15:696–710.

25. Tolstoi LG. Adult-type lactase defi-ciency. Nutr Today 2000;35:134–42;and Lactose intolerance: a self-fulfillingprophecy leading to osteoporosis. NutrRev 2003; 61:221–3.

26. Hertzler and Clancy, Kefir improveslactose digestion; and Martini MC,Smith DE, Savaiano DA. Lactose diges-tion from flavored and frozen yogurts,ice milk, and ice cream by lactase-deficient persons. Am J Clin Nutr1987;46:636–40.

27. Simoons, Primary lactose intolerance.

28. Lactose intolerance: a self-fulfillingprophecy.

29. Lactose intolerance: a self-fulfillingprophecy.

Nutrition UP CLOSEPersonal History of Digestive Upsets

FOCAL POINT: Digestive disorders are common.

To bring you closer to yourdigestive system, review thefollowing list and check the

upsets you have experienced inthe past month:

Experienced inDigestive Upset the Past Month?Heartburn or indigestionDiarrheaConstipationStomach crampsVomitingAbdominal bloatingHemorrhoids

FEEDBACK: Most bouts of digestive upsets are brief and only bothersome. Some will be related todiet (inadequate or excessive dietary fiber, or bacterially contaminated food, for example) whereasothers will be initiated by illness, stress, or another condition. Painful or prolonged episodes ofdigestive disorders should, of course, be brought to the attention of your health care provider.

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