Download How the Body Uses Food: Digestion and Absorption

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Nutrition Scoreboard
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How the Body
Uses Food:
Digestion and
Absorption
2 Disorders of the digestive system are a leading cause
of hospitalizations and medical visits in the United
States and Canada.
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3 Lactose maldigestion is a common digestive disorder.
Answers on next page
1 Almost all of the carbohydrate and fat you consume
in foods is absorbed by the body, but only about half
of the protein is.
• Our bodies are in a continuous state of renewal. Materials used to renew body
tissues come from the food
we eat in the form of
nutrients.
• Digestion and absorption are
ents in foods available for
use by the body.
TRUE
Answers to Nutrition Scoreboard
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KEY CONCEPTS AND FACTS
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1 Over 90% of all the carbohydrates, fats, and proteins
consumed in food are absorbed and become part of
the body.
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• Digestive disorders are
common and often related
to dietary intake.
2 Digestive disorders are the leading cause of hospitalizations among 20- to 44-year-olds in the United
States and Canada. They account for over 70 million
medical visits in the United States each year.1
✔
3 Over half of the world’s population digests lactose
from milk and milk products incompletely or not
at all.2
✔
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processes that make nutri-
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 the
same and you don’t notice the change, the substances that make up the organs and
tissues of your body are constantly changing. Tissues we generally think of as solid
and permanent, such as bones, the heart and blood vessels, and nerves, are continually renewing themselves. The raw materials used in the body’s renewal processes
are the nutrients you consume in foods.
Each day, about 5% of our body weight is replaced by new tissue. Existing components of cells are renewed, the substances in our blood are replaced, and body fluids are recycled. Taste cells, for example, are replaced about every 7 days, and cells
lining the intestinal tract every 1 to 3 days. All of the cells of the skin are replaced
every month. Red blood cells turn over every 120 days. If you thought it was hard
to maintain a car, an apartment, or a house, just imagine what the maintenance is
on a body! Maintenance is just one of the body’s ongoing functions that require
nutrients as raw material.
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How Do Nutrients in Food
Become Available for the Body’s Use?
The human body is an amazing machine. Mine is, anyway. For example, I
regularly 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 them
into useful body parts.3
—Dave Barry, 1987
Index Stock
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The Internal Travels of Food: An Overview] The “food processor” of the body
is the digestive system shown in Illustration 7.1. It consists of a 25- to 30-foot-long
digestion
The mechanical and chemical
processes whereby ingested
food is converted into substances that can be absorbed
by the intestinal tract and utilized by the body.
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The components of food that make “useful body parts” are nutrients. Through the
processes of digestion and absorption, they are made available for use by every cell
in the body.
Oral cavity
Salivary glands
• produce enzymes
that help break down
starch and fats
Tongue
absorption
The process by which nutrients
and other substances are
transferred from the digestive
system into body fluids for
transport throughout the body.
• mastication and
mixing of food
with saliva
Esophagus
• transfers food to
the stomach
Liver
• produces bile that
aids fat digestion
Stomach
Gallbladder
• stores and secretes bile
that aids in fat digestion
• secretes enzymes
that break down
proteins and fats
• mixes and liquifies
food
Bile duct
• conducts bile to
small intestine
Pancreas
Large intestine
(colon)
• secretes enzymes
that break down
carbohydrates,
proteins, and fats
• site of absorption
of water
• site of most
intestinal bacteria
Pancreatic duct
• conducts pancreatic juice
into small intestine
Small intestine
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• secretes enzymes that
break down carbohydrates,
proteins, and fats
• site of nutrient
absorption
Rectum
• stores waste products for
elimination
Anus
• holds rectum closed
• opens to allow
elimination
Illustration 7.1
The digestive system.
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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 absorbed
and 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 fatty
acids and glycerol. Vitamins and minerals are not broken down before they are
absorbed; they are simply released from foods during digestion.
Much of the work of digestion is accomplished by enzymes manufactured by
components of the digestive system such as the salivary glands, stomach, and pancreas. Enzymes are complex protein substances that speed up reactions that break
down food. A remarkable feature of enzymes is that they are not changed by the
chemical 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 carbohydrates, proteins, and fat. Table 7.1 presents information on some of the enzymes
involved in digestion and highlights their specific roles. In Table 7.2 you will see
these enzymes cited in the summary of the processes involved in the digestion of
carbohydrate, fat, and protein.
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monosaccharides
(mono one, saccharide sugar) Simple sugars consisting of one sugar molecule.
Glucose, fructose, and galactose are monosaccharides.
enzymes
Protein substances that speed
up chemical reactions.
Enzymes are found throughout
the body but are present in
particularly large amounts in
the digestive system.
starch
Complex carbohydrates made
up of complex chains of glucose molecules. Starch is the
primary storage form of carbohydrate in plants. The vast
majority of carbohydrate in
our diet consists of starch,
monosaccharides, and
disaccharides.
disaccharide
Simple sugars consisting of two sugar
molecules. Sucrose
(table sugar) consists
of a glucose and a
fructose molecule,
lactose (milk sugar)
consists of glucose
and galactose, and
maltose (malt sugar)
consists of two glucose molecules.
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bile
A yellowish-brown
or green fluid produced by the liver,
stored in the gallbladder, and
secreted into the
small intestine. It
acts like a detergent, breaking down
globs of fat entering
the small intestine
to droplets, making
the fats more accessible to the action
of lipase.
A Closer Look] As you chew food, glands under the tongue release saliva that
lubricates 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 that
begin to break down carbohydrates and fats.
TABLE 7.1
PRIMARY FUNCTION OF SOME DIGESTIVE ENZYMES.
ENZYME
A. Carbohydrate Digestion
Amylase
ENZYME FUNCTION
ENZYME SOURCE
Breaks down starch into smaller
chains of glucose molecules
Produced in the salivary glands
(salivary amylase) and the
pancreas (pancreatic amylase)
Sucrase
Separates the disaccharide sucrose
into glucose and fructose
Produced in the small intestine
Lactase
Splits the disaccharide lactose into
glucose and galactose
Produced in the small intestine
Maltase
Separates maltose into two
molecules of glucose
Produced in the small intestine
Breaks down fats into fragments
of fatty acids and glycerol
Produced in salivary glands
(lingual lipase), and the
pancreas (pancreatic lipase).
The action of lipase is
enhanced by bile
Separates protein into shorter
chains of amino acids
Produced by the stomach
Splits short chains of amino acids
into molecules containing, one,
two or three amino acids
Produced by the pancreas
B. Fat Digestion
Lipase
C. Protein Digestion
Pepsin
Trypsin
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SUMMARY OF THE DIGESTION OF CARBOHYDRATES, FATS, AND PROTEINS.
STOMACH
SMALL INTESTINE,
PANCREAS,
LIVER, AND GALLBLADDER
LARGE INTESTINE
(COLON)
Carbohydrates
(excluding fiber)
The salivary glands
secrete saliva to moisten and lubricate food;
chewing crushes and
mixes it with salivary
amylase that initiates
starch digestion.
Digestion of starch
continues while food
remains in the stomach.
Some alcohol (a
carbohydrate-like substance) is absorbed.
Acid produced in the
stomach aids digestion
and destroys bacteria
in food.
Pancreatic amylase
continues starch digestion. Sucrase, lactase,
and maltase break
down disaccharides
into monosaccharides.
Some alcohol is
absorbed here.
Undigested carbohydrates reach the colon
and are partly broken
down by intestinal
bacteria.
Fiber
The teeth crush fiber
and mix it with saliva
to moisten it for
swallowing.
No action.
Fiber binds cholesterol
and some minerals.
Most fiber is excreted
with feces; some fiber
is digested by bacteria
in the colon.
Fat-rich foods are
mixed with saliva. Small
amounts of lingual
lipase accomplish some
fat breakdown.
Fat tends to separate
from the watery stomach fluid and foods and
float on top of the
mixture. Only a small
amount of fat is
digested. Fat is last to
leave the stomach.
Bile readies fat for the
action of lipase from
the pancreas. Lipase
splits fats into fatty
acids and glycerol
fragments.
A small amount of fatty
materials escapes
absorption and is carried out of the body
with other wastes.
In the mouth, chewing
crushes and softens
protein-rich foods and
mixes them with saliva.
Stomach acid works to
uncoil protein strands
and to activate the
stomach’s proteindigesting enzyme.
Pepsin breaks the protein strands into
smaller fragments.
Trypsin splits protein
into molecules containing one, two, or three
amino acids.
The large intestine carries undigested protein
residue out of the body.
Normally, almost all
food protein is digested
and absorbed.
Fat
Protein
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After food is chewed, it is swallowed and passes down the esophagus to the stomach. Muscles that act as valves at the entrance and exit
Get Your Juices Flowing
of the stomach ensure that the food stays there until it’s liquified, mixed
You don’t have to actually eat food to
with digestive juices, and ready for the digestive processes of the small
start your digestive juices flowing. You
intestine. Solid foods tend to stay in the stomach for over an hour,
just have to think about food or see it.4
whereas most liquids pass through it in about 20 minutes. When the
Put this information to the test. Clear
stomach has finished its work, it ejects 1 to 2 teaspoons of its liquified
your mind, turn the page, and take a
contents into the small intestine through the muscular valve at its end.
close look at Illustration 7.2.
Stomach contents continue to be ejected in this fashion until they are
totally released into the small intestine. These small pulses of liquified
food stimulate muscles in the intestinal walls to contract and relax; these
movements churn and mix the food as it is digested by enzymes. When
the diet contains a lot of fiber and sufficient fluids, the bulge of digesting food in the intestine tends to be larger. Larger food bulges stimulate a higher
level of intestinal muscle activity than do smaller food bulges. Thus, high-fiber meals
pass through the digestive system somewhat faster than low-fiber meals.
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TABLE 7.2
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Michael Newman/PhotoEdit
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circulatory system
The heart, arteries, capillaries,
and veins responsible for circulating blood throughout
the body.
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Illustration 7.3
Scanning electron micrographs of cross sections of
the small intestine (left) and
the large intestine (right).
Note the high density of villi in
the small intestine and the
relative flatness of the lining
of the large intestine.
Absorption] Absorption is the process by which the end products of digestion
are 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
Photo Researchers, Meckes/Ottawa
lymphatic system
A network of vessels that
absorb some of the products of
digestion and transport them
to the heart, where they are
mixed with the substances
contained in blood.
Digestion, as well as the absorption of nutrients, is greatly enhanced by the
structure of the intestines (Illustration 7.3). Fingerlike projections called “villi” line
the inside of the intestinal wall and increase its surface area tremendously. If laid
flat, the surface area of the small intestine would be about the size of a baseball
infield, or approximately 675 square feet. This large mass of tissue requires a high
level of nutrients for maintenance. Much of this need (50% in the small intestine
and 80% in the large intestine) is met by foods that are being digested.5
Digestion is completed when carbohydrates, proteins, and fats are reduced to
substances that can be absorbed, and when vitamins and minerals are released from
food. Most nutrients are absorbed in the small intestine. Water, sodium, and some
of the end products of bacterial digestion, however, are absorbed from the large
intestine. The large intestine is home to many strains of bacteria that consume undigested fiber and other types of complex carbohydrates that are not broken down by
human digestive enzymes. These bacteria excrete gas as well as fatty acids that are
partly absorbed in the large intestine. Substances in food that cannot be absorbed
collect in the large intestine and are excreted in the stools.
Photo Researchers, Prof. P. Motta
Illustration 7.2
Testing, testing. This is a test
of your salivary secretions.
Did the lemon speak directly
to your salivary glands?
If you want to turn the
digestive processes off, quit
thinking about food. Finish
your reading assignment!
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Thymus
Tonsils
Ar teries
Hear t
Spleen
Veins
Lymph
vessels
McMahon
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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 and
circulatory systems. The breakdown products of fat digestion are largely absorbed
into lymph vessels, whereas carbohydrate and protein breakdown products enter
the blood vessels.
The nutrient-rich contents of the lymphatic system are transferred to the bloodstream at a site near the heart where vessels from both systems merge into one vessel. From there the lymph and blood mixture is sent to the heart and subsequently
throughout the body by way of the circulatory system. The circulatory system
reaches every organ and tissue in the body, thereby supplying cells with nutrients
obtained from food.
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Illustration 7.5
(right) The circulatory system
includes the heart and blood
vessels.
This system serves as the nutrient transportation system of
the body.
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Lymph
node
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Illustration 7.4
(left) The lymphatic system.
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Outermost
layer of cells
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Capillary
network
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lllustration 7.6
Structure of villi, showing
blood and lymph vessels.
Lymph vessel
Villi
Vein
Artery
Lymph vessel
heartburn
A condition that results when
acidic stomach contents are
released into the esophagus,
usually causing a burning
sensation.
hemorrhoids (hem-or-oids)
Swelling of veins in the anus
or rectum.
irritable bowel syndrome
(IBS)
A disorder of bowel function
characterized by chronic or
episodic gas, abdominal pain,
diarrhea or constipation, or
both.
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duodenal (do-odd-en-all)
and stomach ulcers
Open sores in the lining of the
duodenum (the uppermost part
of the small intestine) or the
stomach.
Muscle
tissue
Beyond Absorption} Cells can use nutrients directly for energy, body structures, or
the regulation of body processes, or convert them into other usable substances. For
example, glucose delivered to cells can be used “as is” for energy formation or converted to glycogen and stored for later use. Fatty acids, an end product of fat digestion, can be incorporated into cell membranes or used in the synthesis of certain
hormones. Vitamins and minerals freed from food by digestion can be used by cells
to control enzyme activity or can be stored for later use. The body has a limited storage capacity for some vitamins and minerals. Consequently, excessive amounts of
certain vitamins and minerals such as vitamin C, thiamin, and sodium are largely
excreted in urine.
Digestion and Absorption Are Efficient} Of our intake of energy nutrients, approximately 99% of the carbohydrate, 92% of the protein, and 95% of the fat we consume in food are digested and absorbed. Dietary fiber, however, leaves the digestive
system in much the same form as it entered. Humans don’t have enzymes that break
down fiber. It should be noted, however, that some fiber is digested in the large intestine by bacteria.
Digestive Disorders Are Common
Excluding childbirth, digestive disorders such as heartburn, hemorrhoids, irritable
bowel syndrome, and duodenal and stomach ulcers are the leading cause of hospitalization among U.S. and Canadian adults aged 20–44 years. They account for over
70 million medical visits yearly in the United States alone.6 Table 7.3 shows the percentages of U.S. adults who have common digestive disorders. Digestive disorders
are common in children as well as adults. At least one-third of U.S. adults experience heartburn, and up to 28% of school children experience constipation.8
Constipation and Hemorrhoids] Both constipation and hemorrhoids are often
due to diets that provide too little fiber. Fiber intakes by adults of 25 to 30 grams
per day along with plenty of fluids (8 to 12 cups a day) can help prevent constipa-
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COMMON DIGESTIVE
DISORDERS.7
U.S. ADULTS AFFECTED*
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Ulcers and Heartburn] Ulcers develop when the protective barrier formed by
cells 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 of
the stomach and duodenum and cause an “ulcer.” Duodenal ulcers are ten times
more common than stomach ulcers and are closely associated with the presence of
Helicobacter pylori (H. pylori) bacteria.9 H. pylori infects and irritates the lining of
the stomach. The infection is acquired by the ingestion of foods and other substances contaminated with saliva, vomit, or feces from people harboring the bacteria in their stomach. Rates of H. pylori infection are highest in countries with poor
sanitary conditions.10 Excessive production of stomach acid can lead to ulcers, too,
and may also cause heartburn. Heartburn is unrelated to heart conditions. It is
called that because acid that escapes from the stomach causes a burning sensation
in an area of the esophagus located near the heart.
Stress, anxiety, and frequent use of aspirin, ibuprofen, naproxen, and other
medications appear to be related to the development of ulcers and heartburn in
some people.11 Fatty foods, coffee, alcohol, citrus fruits, soft drinks, and a variety
of other foods have been implicated in the development of ulcers and heartburn.
Rather than cause these disorders, certain foods appear to aggravate the symptoms
of ulcers and heartburn. High-fiber diets, on the other hand, appear to be protective
against the development of ulcers and heartburn.12
A number of medications are available for the treatment of H. pylori and the
excessive production of stomach acid. Reduction of stress, judicious elimination of
offending foods and beverages from the diet, and small, frequent meals also help
relieve ulcers and heartburn in some people.13
TABLE 7.3
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tion and hemorrhoids in healthy people. Some good sources of dietary fiber are
shown in Illustration 7.7.
Heartburn
33.0%
Hemorrhoids
12.8
Irritable bowel
syndrome
6–12%
Ulcers
3.5
Chronic
constipation
3.0
Chronic diarrhea
1.2
*Noninstitutionalized adults experiencing the disorder in the past 12
months.
Richard Anderson
Irritable Bowel Syndrome] Irritable bowel syndrome, abbreviated IBS, is not
considered 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
lllustration 7.7
Food sources of dietary fiber.
Together, the foods shown provide 29 grams of dietary fiber,
an amount that helps prevent
constipation.
1 mango (4 g)
All Bran Cereal, 1/3 c. (10 g)
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1/2 c. lima beans
(5 g)
1 pear with skin (4 g)
1/2 c. corn (3 g)
1/2 c. carrots (2.8 g)
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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 a
low-fat diet (25% of calories), counseling, and over-the-counter fiber powders,
antidiarrhea pills, and pain medications. More serious cases may respond to stress
reduction, eating in relaxed surroundings, antidepressants, and drugs that reduce
colon muscle spasms. Probiotics, or “friendly” bacteria that help colonize the colon
with microorganisms that help protect and heal the colon lining, are being increasingly used for this disorder.14
probiotics
Non-harmful bacteria and
some yeasts that help colonize
the intestinal tract with beneficial microorganisms and that
sometimes replace colonies of
harmful microorganisms. Most
common probiotic strains are
Lactobacilli and Bifidobacteria.
diarrhea
The presence of three or more
liquid stools in a 24-hour
period.
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lic health problem in developing countries. Most cases of diarrhea are due to bacterial- or viral-contaminated food or water, lack of immunizations against infectious
diseases, and vitamin A, zinc, and other nutrient deficiencies that make children particularly susceptible to diarrhea. Diarrhea can deplete the body of fluid and nutrients 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 estimated 3.5 million deaths from diarrhea diseases occur each year to the world’s population of children 5 years of age or under.15
The vast majority of cases of diarrhea can be prevented through food and water
sanitation programs, immunizations, and adequate diets. The early use of oral rehydration fluids (for example, the formula provided by the World Health Organization and commercial formulas such as Pedialyte and Rehydralyte) shortens the
duration of diarrhea. Rehydration generally takes 4 to 6 hours after the fluids are
begun.16
Rather than “resting the gut” during diarrhea as used to be recommended, children 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 needed
for the repair of the intestinal tract. It is best to avoid sugary fluids such as soft
drinks. High-sugar beverages tend to draw fluid into the intestinal tract rather than
increase the absorption of fluid.17
Flatulence] Everyone experiences flatulence—it’s normal. Gas can occur in the
esophagus, stomach, small intestine, and large intestine due to swallowed air or bacterial breakdown of food in the large intestine. Air may be swallowed along with
food and beverages or while chewing gum. Eating and drinking while in a rush generally increases air ingestion. Bacterial production of gas in the large intestine may
be related to the ingestion of dried beans, broccoli, cauliflower, brussels
sprouts, onions, corn, and other vegetables containing a type of complex
carbohydrate that bacteria, but not humans, can break down. Fructose,
Ancient Perspectives on Flatulence
which is used to sweeten a variety of food products and beverages, and
sorbitol (used in some types of candy and gum) may lead to gas formaPassing gas is
tion by bacteria that produce gas as a waste product of carbohydrate
necessary to
digestion. Heartburn and other gastrointestinal tract disorders and medwell-being.
ications such as antibiotics are also associated with gas production.18
—Hippocrates
People often think they produce too much gas, even when they don’t.
All Roman citizens
The amount of gas swallowed and produced by gut bacteria varies a
shall be allowed to
good deal among individuals, and within the same individual. Gas propass gas whenever
duction changes depending on what foods are eaten, the types of bactenecessary.
ria populating the large intestine, the medications used, and the presence
—Claudius
of gastrointestinal tract disorders. Severe and painful symptoms related
to gas production may signal the presence of a digestive disorder.19
flatulence (flat-u-lens)
Presence of excess gas in the
stomach and intestines.
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Diarrhea] Diarrhea is a common problem in the United States and a leading pub-
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ESTIMATED INCIDENCE OF
LACTOSE MALDIGESTION
AMONG OLDER CHILDREN
AND ADULTS IN
DIFFERENT POPULATION
GROUPS.22
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your stomach growls, you know that gas and food or fluids are mixing in your
stomach. The growling tends to be louder when your stomach is empty, when
there’s no food to muffle the noise. It can occur anytime, whether your stomach is
empty or full, but is more likely to happen when your stomach is empty.20
TABLE 7.4
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Stomach Growling] Gas in the stomach can make your stomach growl. When
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 milk
and milk products presents a problem for most of the world’s adults, who cannot
digest it, either partially or completely (Table 7.4).21 The condition occurs more
commonly in population groups that have no historical links to dairy farming and
milk drinking.23 Early humans in central and northwestern Europe and the regions
of Africa and China highlighted in Illustration 7.8 tended to raise dairy animals and
drink milk.
Lactose maldigestion is caused by a genetically determined low production of
lactase, the enzyme that digests lactose. People who lack this enzyme end up with
free lactose in their large intestine after they consume milk or milk products that
contain lactose. The presence of lactose in the large intestine produces the symptoms
of lactose intolerance. These symptoms include a bloated feeling and diarrhea due
to fluid accumulation, and gas and abdominal cramping caused by the excretion of
gas by bacteria that digest lactose.
INCIDENCE OF LACTOSE
MALDIGESTION
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 maldigestion
A disorder characterized by
reduced digestion of lactose
due to the low availability of
the enzyme lactase.
lactose intolerance
The term for gastrointestinal
symptoms (flatulence, bloating, abdominal pain, diarrhea,
and “rumbling in the bowel”)
resulting from the consumption of more lactose than can
be digested with available
lactase.
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Lactose digestion
Lactose maldigestion
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Illustration 7.8
Lactose maldigestion is less common among descendants of people who consumed milk
from domesticated animals during prehistoric times (light areas) than among people
whose early ancestors did not drink milk (dark areas).24
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Lactose maldigestion is rare in young children and affects adults to various
degrees. Some adults produce little or no lactase and develop symptoms of lactose
intolerance when they consume only small amounts of milk or milk products. Others produce some lactase and can tolerate limited amounts of lactose-containing
milk 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 may
improve lactose digestion due to enhanced bacterial breakdown of lactose in the gut.25
Many people who are lactose maldigesters have no trouble eating
“Brain freeze,” or that splitting
yogurt
and other fermented milk products such as cultured buttermilk,
headache you can get from eating ice
kefir,
and
aged cheese. The bacteria used to culture yogurt can digest
cream too fast, is caused by the quick
half
or
more
of the lactose. This reduction in lactose content is sufficient
drop in temperature in the back of
to
prevent
adverse
effects in many people with lactose maldigestion.26
your mouth. That causes vessels to
Milk
solids,
milk,
and other lactose-containing components of milk
constrict, and the result is an “ice
may
be
added
to
foods
you wouldn’t expect. Consequently, it’s best to
cream headache.”
examine food ingredient labels when in doubt. Milk, for instance, is a
primary ingredient in some types of sherbet, and milk solids are added
to many types of candy.
Do You Have Lactose Maldigestion?] The single most reliable indi-
R
Richard Anderson
cator of lactose maldigestion is the occurrence of lactose intolerance
within hours after consuming lactose.27 If you consistently experience
these symptoms (described earlier), visit your health care provider for a
diagnosis. The symptoms could be due to lactose, other substances in
milk, or another problem.
FO
Illustration 7.9
Dairy products generally well tolerated by people with
lactose maldigestion.
How Is Lactose Maldigestion Managed?] Lactose
maldigestion should not be managed by omitting milk and
milk products from the diet! Doing so would exclude a
food group that contributes a variety of nutrients that cannot easily be replaced by other foods. The omission of milk
and milk products from the diet of people with lactose
intolerance promotes the development of osteoporosis.28
Rather, fortified soy milk, low-lactose cow’s milk, milk pretreated with lactase drops, and yogurt and other fermented
milk products (if tolerated) should be consumed. Illustration 7.9 shows a variety of dairy products that are generally well tolerated by people with lactose maldigestion.
Lactase tablets are also available and should be taken
within 30 minutes of consuming lactose.29 Lactase is an
enzyme, and enzymes are made of protein. Protein is partially digested in the stomach, so some of the lactase
ingested in the tablets may not reach the small intestine
where it is needed if the tablets are taken too far in advance
of eating.
Digestion is a remarkably complex and efficient process
that could be covered in much more detail than has been presented here. Readers are encouraged to consult the Web sites
listed at the end of the unit for additional information.
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Key Terms
enzymes, page 7–4
lymphatic system, page 7–6
bile, page 7–4
flatulence, page 7–10
monosaccharides, page 7–4
circulatory system, page 7–6
heartburn, page 7–8
probiotics, page 7–10
diarrhea, page 7–10
hemorrhoids, page 7–8
starch, page 7–4
digestion, page 7–3
irritable bowel syndrome (IBS),
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absorption, page 7–3
disaccharide, page 7–4
duodenal and stomach ulcers,
page 7–8
page 7–8
lactose intolerance, page 7–11
lactose maldigestion, page 7–11
www links
www.healthfinder.gov
Search digestive diseases by name, or
search “digestion.”
www.navigator.tufts.edu
Nutrition Navigator will help you find the
most reliable sites on topics related to
digestion.
digestive.niddk.nih.gov
NIH’s National Digestive Disease Clearinghouse homepage. This site provides links to
information about specific digestive diseases, clinical trials, statistics, and answers
to questions such as Why do I have gas?
www.nlm.nih.gov/medlineplus
Find out more about digestion, absorption,
organs of the gastrointestinal tract, and
digestive diseases at this site.
Notes
1. Digestive disease statistics, National
Digestive Disease Clearinghouse,
http://digestive.niddk.nih.gov/statistics/
statistics.htm, accessed 8/03; and Leading causes of hospitalization in Canada.
Health Canada, Population and Public
Health Branch, www.hc-sc.gc.ca,
accessed 8/03.
2. Hertzler SR, Clancy SM. Kefir improves
lactose digestion and tolerance in adults
with lactose maldigestion. J Am Diet
Assoc 2003; 103:582–74.
3. Leading causes of hospitalization in
Canada (www.hc-sc.gc.ca).
4. Schneeman B. Nutrition and gastrointestinal function. Nutr Today 1993;Jan/
Feb:20–24.
5. Bengmark S. Econutrition and health
maintenance: a new concept to prevent
GI 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 hospitalization in Canada (www.hc-sc.gc.ca).
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7. Digestive disease statistics (http://
digestive.niddk.nih.gov/statistics/
statistics.htm); Leading causes of hospitalization in Canada (www.hc-sc.gc.ca).
8. Borowitz SM et. al. Precipitants of constipation during early childhood. J Am
Fam Pract 2003;16:213–8.
9. Current medical diagnosis and treatment, 35th ed. Stamford (CT): Appleton
& Lange; 1997.
10. Suerbaum S, Michetti P. Helicobacter
pylori infection. N Engl J Med 2002;
347:1175–86.
11. Kurata AN, et al. Dyspepsia in primary
care: perceived causes, reasons for
improvement, and satisfaction with care.
J Fam Practice 1997;44:281–8.
12. The Merck manual of medical information. Whitehouse (NJ): Merck Research
Laboratory; 2000; and Suerbaum and
Michetti, Helicobacter pylori infection.
13. Kurata et al., Dyspepsia in primary care.
14. Irritable bowel syndrome. American
Gastroenterologial Association Medical
Position Statement. Gastoenterol 1997;
112:2118–9; and Barclay L. Highlights
from digestive diseases week. An expert
interview with Lawrence R. Schiller.
Medscape Medical News, 2003,
www.medscape.com.
15. Kilgore PE, et al. Trends in diarrheal
disease associated mortality in US children, 1968 through 1991. JAMA 1995;
274:1143–8.
16. Kilgore et al., Trends in diarrheal disease; Goepp JG, Katz SA, Oral rehydration therapy, Am Fam Phys 1993;47:
843–8; and Meyers A. Oral rehydration
therapy: what are we waiting for? Am
Fam Phys 1993;47:740–2.
17. Lima AAM, Guerrant RL. Persistent
diarrhea in children: epidemiology, risk
factors, pathophysiology, nutritional
impact, and management. Epidemiol
Rev 1992;34:222–42; and Goepp and
Katz, 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.scientific
american.com, accessed 8/03.
21. Hertzler and Clancy, Kefir improves lactose digestion.
22. Scrimshaw NS, Murray, EB. Prevalence
of lactose maldigestion. Am J Clin Nutr
1988;48(suppl):1086–98; and InmanFelton AE. Overview of lactose
maldigestion (lactose nonpersistence).
J Am Diet Assoc 1999;99:481–9.
23. Simmons FJ. Primary adult lactose intolerance and the milking habit: a problem
in biological and cultural interrelationships. I. Review of the medical research.
Am J Digestion 1981;14:819.
24. Simoons FJ. Primary lactose intolerance
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27. Simoons, Primary lactose intolerance.
28. Lactose intolerance: a self-fulfilling
prophecy.
29. Lactose intolerance: a self-fulfilling
prophecy.
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25. Tolstoi LG. Adult-type lactase deficiency. Nutr Today 2000;35:134–42;
and Lactose intolerance: a self-fulfilling
prophecy leading to osteoporosis. Nutr
Rev 2003; 61:221–3.
26. Hertzler and Clancy, Kefir improves
lactose digestion; and Martini MC,
Smith DE, Savaiano DA. Lactose digestion from flavored and frozen yogurts,
ice milk, and ice cream by lactasedeficient persons. Am J Clin Nutr
1987;46:636–40.
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and the milking habit: a problem in
biological and cultural interrelationships. Am J Digestive Diseases
1970;15:696–710.
Nutrition
UP CLOSE
Personal History of Digestive Upsets
FOCAL POINT: Digestive disorders are common.
To bring you closer to your
digestive system, review the
following list and check the
Digestive Upset
Heartburn or indigestion
Diarrhea
Constipation
Stomach cramps
Vomiting
Abdominal bloating
Hemorrhoids
upsets you have experienced in
the past month:
Experienced in
the Past Month?
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FEEDBACK: Most bouts of digestive upsets are brief and only bothersome. Some will be related to
diet (inadequate or excessive dietary fiber, or bacterially contaminated food, for example) whereas
others will be initiated by illness, stress, or another condition. Painful or prolonged episodes of
digestive disorders should, of course, be brought to the attention of your health care provider.