The stress response is modified by hormones, and sustained, elevated adrenal hormones due to prolonged stress affect the immune system and decrease the immune response to foreign invader
Trang 1356
iatrogenic malnutrition See HOSPITAL-INDUCED
MALNUTRITION
IBD See INFLAMMATORY BOWEL DISEASE
IBS See IRRITABLE BOWEL SYNDROME
iceberg lettuce See LETTUCE
ice cream A frozen DESSERTcontaining flavored,
sweetened frozen cream and MILK products, and
SUGAR Frozen desserts based on EGGS, cream, and
milk were apparently invented in the 1600s,
although frozen blends of fruits were served in
ancient China, where salt mixtures were used to
lower the temperature below freezing Americans
eat an average of 15 quarts a year per person
Ice cream is a high-CALORIE, high-FAT, and
high-sugar food Unless it is homemade, ice cream will
usually contain artificial coloring, flavorings, and
stabilizers such as LOCUST BEAN GUM, GUAR GUM,
CARRAGEENAN, GELATIN, and alginic acid or cellulose
derivatives Federal law requires that ice cream
contain at least 10 percent fat (BUTTERFAT), and
most regular ice creams provide 10 percent to 12
percent butterfat Super-premium vanilla ice cream
contains 16 percent to 20 percent butterfat In
con-trast, ice milk contains 2 percent to 7 percent fat,
while sherbet contains 1 percent to 2 percent fat
Ice cream usually contains sugar or other
sweeten-ers and emulsifisweeten-ers like POLYSORBATES and MONO
-GLYCERIDESstabilize ice cream during processing
Nondairy frozen desserts resembling ice cream
have no legally defined butterfat content, and
although they are low-fat options, sometimes these
desserts have more total calories per serving than
traditional ice cream due to their high sweetener
content
One cup of rich vanilla-flavored ice cream with about 16 percent fat provides: 349 calories; protein, 4.1 g; carbohydrate, 32 g; fat 23.7 g; cholesterol, 88 mg; calcium 151 mg; vitamin A, 219 retinol equiv-alents; thiamin, 0.04 mg; riboflavin, 0.28 mg; niacin, 0.12 mg
One cup of regular vanilla ice cream with about
11 percent fat provides: 269 calories; protein, 4.8 g; carbohydrate, 31.7 g; fat, 14.3 g; cholesterol, 59 mg; calcium, 176 mg; vitamin A, 133 retinol equiv-alents; and similar amounts of thiamin, riboflavin, and niacin to those found in rich vanilla ice cream One cup of vanilla-flavored ice milk with about
4 percent fat provides: 184 calories; protein, 5.2 g; carbohydrate, 29 g; fat, 5.6 g; cholesterol, 18 mg; calcium, 176 mg; vitamin A, 52 retinol equivalents; and similar amounts of other vitamins (See also
DAIRY-FREE FROZEN DESSERTS; DIETARY GUIDELINES FOR AMERICANS.)
ideal body weight An outmoded standard for body weight that originated from data collected by U.S life insurance companies from their policy holders who lived the longest Ideal body weight was listed as the average weight for a given age, height, body, or “frame” size From these data grew the classic definition for OBESITYas a weight
20 percent greater than the ideal body weight Part
of the problem with this standard of ideal body weight lies in the nature of HEIGHT-WEIGHT TABLES Weight charts and tables do not take into account individual variations in body structure (muscles and bone mass); consequently, there is no stan-dard for measuring small, medium, or large body frames
There is no single ideal body weight for a group
of people because every person has an individual, desirable weight Selecting a realistic body weight
as a goal has proven to be far more useful than
Trang 2striving for a rigidly defined standard A realistic
body weight is one that can be readily maintained
without intermittent DIETING
A measure of body FATis more useful than total
body weight because body weight may not
corre-late with the amount of fat on a lean person
Fur-thermore, ideal body weight provides no indication
of fat distribution Some fat deposits are riskier for
heart disease than others Methods of accurately
measuring body fat at clinics include buoyancy
testing with underwater weighing (requiring a
spe-cial tank) and SKIN FOLD thickness measured by
skin calipers or by skin resistance measurements
Suggestions for estimating an optimal body
weight include: For males, take 106 pounds for the
first 5 ft of height, then add six pounds for each
additional inch of height For females, take 100
pounds for the first 5 ft., then add five pounds for
each additional inch (See also BODY MASS INDEX;
FAT-FOLD TEST.)
idiopathic A medical term that is applied to a
disease or condition arising spontaneously from an
unknown cause Idiopathic GOUT and high blood
pressure are examples
ileitis See CROHN’S DISEASE
ileum The last three-fifths of the small INTESTINE
that joins the large intestine (COLON) The length of
the ileum varies among individuals, ranging from
15 to 30 ft in adult men The ileum absorbs FAT,
fat-soluble vitamins, CALCIUM, MAGNESIUM, VITAMIN
B12, and AMINO ACIDS BILE salts, which act as the
detergents in bile required for fat DIGESTION, are
also absorbed in the ileum and are recycled by the
liver to released once again in bile
Flow of material between the ileum and colon is
regulated by the ileocecal valve (See also ENTERO
-HEPATIC CIRCULATION.)
illness Ill health or disease; the opposite of
well-ness Illness reflects imbalanced body functions and
can thus be regarded as a change away from the
healthy state, in which all systems function within
normal limits (HOMEOSTASIS)
An illness may be localized, in which a limited
region of the body is affected, or it may be systemic,
in which several parts of the body or the whole body are affected Pain is often associated with illness, although pain is not equivalent to disease Pain gen-erally indicates that an imbalance exists in the body The imbalance could reflect an unhealthy lifestyle, such as dietary excess or deficiency, or it could be associated with infection and inflammation Most illnesses are self-limiting, meaning that the body generally can cure itself when given the oppor-tunity It is now clear that the body’s systems work together to maintain health Particularly important are the IMMUNE SYSTEM, the NERVOUS SYSTEM, and the
ENDOCRINE SYSTEM (hormone-producing system)
An imbalanced immune system affects the brain, and the brain alters immunity and hormone pro-duction Hormones in turn affect nerve function
As an example, perceived STRESScan trigger a FIGHT
OR FLIGHT RESPONSE by the brain The stress response is modified by hormones, and sustained, elevated adrenal hormones due to prolonged stress affect the immune system and decrease the immune response to foreign invaders
Whether or not an individual becomes ill depends on a complex interplay of many factors, broadly categorized according to medical history and environmental influences Family history reflects patterns of inheritance, over which one has
no control Genetic predisposition thus increases the risk of many chronic, degenerative diseases of
AGING, such as OSTEOPOROSIS, heart disease and
STROKE, high blood pressure, and DIABETES Health history can have a profound effect on susceptibility
to illness Thus, prior injury, deficiency, or illness can set the stage for a subsequent illness For example, arthritis can begin at the site of a former injury, and prolonged treatment with a broad-spec-trum antibiotic can destroy beneficial gut bacteria and promote a yeast infection Prior drug treatment can alter the body’s ability to destroy alcohol, and pretreatment with alcohol can alter the body’s abil-ity to degrade many drugs In terms of public health, immunization against polio, flu, or tetanus reduces the risk of these diseases At the beginning
of the 20th century, niacin deficiency caused wide-spread pellagra and associated mental illness in the South The enrichment of bread and grain products with the B vitamin NIACINin the 1920s essentially eliminated pellagra as a public health issue in the United States
illness 357
Trang 3Due to differences in inheritance and
environ-ment, toxic exposure, nutritional status, and
med-ical history, each person is biochemmed-ically unique
Thus, individuals vary in their ability to protect
themselves against damaging effects of FREE RADI
-CALS, and to detoxify potentially dangerous
chemi-cals that they eat or drink or breathe at home or in
the workplace
Although neither a family history nor a medical
history can be altered, lifestyle choices can
pro-foundly impact susceptibility to illness The most
frequently cited RISKfactors for illness and
prema-ture death include the use of tobacco and alcohol,
accidental injury, unwanted pregnancy, drug
abuse, and inadequate nutrition The growing
awareness that prevention is the most
cost-effec-tive and permanent solution to many health issues
has lead many physicians to work with their
patients as partners in health to empower them in
making healthful choices for themselves and their
families
This approach could possibly decrease American
deaths before the age of 65 by two-thirds, even
without further breakthroughs in medicine and
nutrition
Prevention and Personal Responsibility
The health-conscious individual can focus on four
essential steps in maintaining health and preventing
illness: positive attitude, a healthy diet, regular
exer-cise and minimizing toxic exposures Humanistic
psychology emphasizes the importance of a positive
mental attitude in preventing illness and
maintain-ing health The immune system and the repair
mechanisms of tissues are well designed to ward off
infection, to cure disease and to repair injury
DEPRESSION seems to diminish this capacity For
example, depression causes a drop in the production
of interleukin, proteins that help regulate the
immune response and help activate cancer-killing
lymphocytes Clinical statistics in the United States
suggest psychological stress can harm the heart,
increasing the risk of rehospitalization among
patients with cardiac problems Group therapy,
meditation, and other practices may improve
car-diovascular health in patients with clogged arteries
by modifying their response to psychological stress
Susceptibility to disease reflects nutritional
sta-tus; the nutritional environment affects the
expres-sion of inherited traits Either overnutrition or
UNDERNUTRITION can set the stage for chronic ill-ness Excessive fat consumption increases the risk
of cancer and obesity, while inadequate amounts of most nutrients eventually lower the body’s defense against disease, including cancer On the other hand, a healthy diet provides optimal amounts of all nutrients to assure health, while avoiding detri-mental food constituents
Probably the best strategies to avoid chronic ill-ness associated with aging are regular physical exercise coupled with wise food choices A seden-tary lifestyle is linked to an estimated 250,000 deaths annually in the United States Exercise decreases the risk of heart disease, stroke, high blood pressure (hypertension), adult onset dia-betes, osteoporosis (thin bone disease), and colon and breast cancer
Minimizing exposure to potentially damaging agents such as solvents, pollutants, and cigarette smoke is also important The amount, type, and length of exposure to a toxic material at home or in the workplace affects health Only recently have studies been undertaken to determine additive, long-term effects on health of continued low level-exposure to pesticides and industrial pollutants in food and water and air (See also ANTIOXIDANT; BIO
-CHEMICAL INDIVIDUALITY; DEGENERATIVE DISEASES;
DETOXIFICATION.)
imitation fat See FAT SUBSTITUTE; OLESTRA; SIMP
-LESSE
imitation flour See FLOUR SUBSTITUTE
imitation food A processed food that is nutri-tionally inferior to the real food The designation
“nutritionally inferior” on a food label means that the food contains 10 percent less of one or more nutrients than the food for which it substitutes The food industry has devoted considerable finan-cial resources toward producing imitation food, most often substitutes for MEAT, FISH, dairy prod-ucts, and FRUIT For example, SURIMI is imitation seafood Compared to real foods, imitation foods often have a longer shelf life and may be tastier Food additives are carefully selected for this pur-pose Imitation foods are often less expensive than
358 imitation fat
Trang 4the real foods, but are generally less nutritious than
the foods they replace because processing destroys
or removes important nutrients Relatively few
nutrients are added back
Current regulations specify that food labels must
list ingredients in descending order according to
weight, meaning that the first ingredient listed is the
most predominant If the first item listed on the food
label is one of the following, the food is likely to be
fabricated or highly processed: any natural
sweet-ener such as corn sweetsweet-ener, high FRUCTOSE CORN
SYRUP, HONEY, DEXTROSE, SUCROSE, or corn syrup
solids; TEXTURIZED VEGETABLE PROTEIN; and sodium
caseinate The presence of artificial food colors, MSG
(MONOSODIUM GLUTAMATE), COCONUT OIL, palm or
palm kernel oil, and PRESERVATIVESalso indicates that
the food is imitation or highly processed (See also
CONVENIENCE FOOD; FOOD ADDITIVES; FOOD LABELING.)
immune system An elaborate, finely tuned
defense system to destroy and counter the effects of
viruses, bacteria, yeasts, and foreign substances
that operate within tissues and cells and in the
bloodstream The immune system recognizes “self”
from “nonself,” substances not part of the body
Another feature of the immune system is memory
It can remember previous invaders and mount a
rapid response to them when they reappear When
the immune system is healthy, it destroys foreign
elements without causing symptoms, but an
imbal-anced immune system can set the stage for disease
Foreign substances and microorganisms may not
be recognized or destroyed, resulting in chronic
infection or even CANCERand AIDS An imbalanced
immune system can attack the body’s own tissues,
creating AUTOIMMUNE DISEASES, or it can
over-respond to common substances, creating allergies,
such as food allergies
Organization of the Immune System
The two branches of the immune system are
“cel-lular immunity” and “humoral immunity.” The
first depends on the active participation of different
types of cells Cellular immunity includes
macro-phages, cells that engulf foreign invaders These
scavengers are amoebalike cells that surround and
digest foreign particles, viruses, and bacteria
Macrophages live in tissues like the spleen
(spleno-cytes), the LIVER(Kupffer cells), the lymph
(wan-dering macrophages), the spinal cord, the brain (microglia), and connective tissue
Lymphocytes are an important type of white blood cell T cells are highly specialized lympho-cytes that attack viruses, tumors, and transplanted cells and regulate the immune system T cells are processed by the THYMUS GLAND They work with B cells, which produce defensive proteins called ANTI
-BODIES In a typical scenario, macrophages first engulf foreign materials called ANTIGENSand trans-form fragments of the antigens for display on their cell surfaces Certain T “helper” cells, acting as
“generals,” “read” these antigens, and in turn stim-ulate the production of specialized T “killer” cells, foot soldiers that destroy abnormal cells or foreign materials The gut is the largest immune organ, which is called the Gut-associated lymphoid tissue (GALT) GALT produces more antibodies than any other tissue in the body
The different types of immune cells communi-cate with each other via protein messengers called
LYMPHOKINES For example, macrophages produce a lymphokine called interleukin-1 to activate T helper cells, which in turn produce interleukin-2,
to stimulate the production of the killer T cells Helper T cells also produce gamma INTERFERON, which activates killer T cells
Mast cells are a type of T cell that lives in tissues and fights local infection When they contact for-eign materials and cells, mast cells destroy them Mast cells also release special chemicals like HISTA
-MINE, as well as certain lymphokines that trigger inflammation marked by swelling (EDEMA), red-ness, itching, sneezing, and runny nose Lym-phokines also trigger phagocytes (macrophages) to destroy foreigners and dispose of signal proteins once they have done their work
Humoral immunity pertains to blood and lymph It relies on cells that release defensive PRO
-TEINS called complement and antibodies into the bloodstream to fight infection Antibodies (gamma globulins) are Y-shaped proteins designed to target
a particular antigen, by which a substance is recog-nized as being foreign An antibody can neutralize the enemy either by binding to it or by targeting it for attack by other cells and chemicals After anti-bodies bind foreign cells, complement ruptures them Complement also triggers localized inflam-matory reactions, leading to common symptoms of
immune system 359
Trang 5pain, redness, and swelling, as well as to an
increased concentration of defensive cells at the
point of injury or infection
B cells, which originate in bone marrow, are a
type of lymphocyte that yield plasma cells,
special-ized to produce antibodies when exposed to foreign
invaders B cell proliferation, maturation, and
anti-body production are stimulated by T helper infected
cells Another type of T cell, called T suppressor
cells, gear down the immune system by turning off
B cell production Thus T suppressor cells limit
aller-gic attacks and auto-immune reactions
Immunity
Immunity is a hallmark of the immune system
The recovery from an infection renders the
indi-vidual immune to subsequent attack by the
partic-ular disease-causing agent Immunity to chicken
pox is a common example The underlying
mecha-nism relies on memory T and memory B cells in
the bloodstream, which signal a red alert for a
quick attack the next time a conquered virus
in-vades again These memory cells multiply rapidly
when they again encounter any antigen they
remember
Nutrients that May Benefit the Immune System
The immune system requires a rich array of
nutri-ents, including protein, FATTY ACIDS, VITAMINS, and
MINERALS, for normal function A JUNK FOOD diet
can lead to overnutrition (too many calories and
fat) and malnutrition (too little trace minerals and
vitamins) that weaken the immune system
Mal-nourished individuals lacking adequate protein or
calories are prone to disease Low-level deficiencies
of many nutrients seem to lower the effectiveness
of the immune system Supplements can boost
immunity, especially in elderly people It seems
clear that a wise approach to support the immune
system nutritionally includes a varied
diet—reduc-ing fat to less than 30 percent of daily calories and
emphasizing whole foods, FRUITS, and VEGETABLES,
especially those rich in VITAMIN C, BETA-CAROTENE,
and other carotenoids Supplementing the diet
with 100 percent of the RDA, (RECOMMENDED
DIETARY ALLOWANCE) of B vitamins and trace
min-erals for insurance may also be prudent when a
diet is compromised by junk food or when the diet
provides fewer than 1,600 calories
ANTIOXIDANT nutrients such as vitamin C, VITA
-MIN E, SELENIUM, COPPER, MANGANESE, and beta-carotene may enhance immune responses by lowering the burden of FREE RADICALS, thus pro-tecting immune cells against the cumulative oxida-tion and free radical attack due to the release of powerful oxidizing agents as superoxide, hydrogen peroxide, and hydroxyl radicals
Vitamin C deficiency lowers the immune response in animal models Adequate vitamin C increases T and B cell production and helps attack-ing cells migrate to sites of infection while makattack-ing viruses and bacteria more sensitive to destruction Furthermore, vitamin C acts as an antioxidant, and
it protects cells against reactive chemicals produced
by mast cells used to destroy foreigners
Vitamin E enhances both humoral and cell-mediated immunity, while vitamin E deficiency contributes to reduce T cells, killer cells, and macrophage function Vitamin E supplementation boosts the immune system in elderly men and women consuming a typical diet, suggesting that older people require more vitamin E than specified
by the adult Recommended Dietary Allowance to assure a fully functional immune system
Selenium is a cofactor for an important antioxi-dant enzyme, glutathione peroxidase, which neu-tralizes lipid peroxide that could damage the immune cells Selenium works with vitamin E to stimulate the immune response to infection in experimental animals Together they may help pro-tect against cancer Selenium increases T helper cells and increases antibody production in experi-mental animals However, excessive selenium depresses the immune system
Other specific nutrients support the function of the immune system:
FOLIC ACID is required for immunity and lym-phocyte production Folic acid is often deficient in the American diet
IRON is required to produce T and B cells Iron deficiency is associated with increased incidence of common infection among children
MAGNESIUM is needed by the complement sys-tem to activate phagocytes It is also required for antibody production Americans typically do not consume enough magnesium
PANTOTHENIC ACIDand VITAMIN B6help keep the lymphatic system and thymus gland healthy
360 immune system
Trang 6VITAMIN Aand beta-carotene help maintain
thy-mus gland function during stress Overproduction
of cortisol, a stress-induced hormone from the
adrenal glands, tends to shrink the thymus gland,
which is critical for fully functioning T cells
Beta-carotene is the precursor of vitamin A Limited
studies suggest that beta-carotene may also
stimu-late helper T cells Studies of children in developing
nations indicate that there is a direct relationship
between vitamin A deficiency and decreased
resis-tance to infection On the other hand, excessive
vitamin A can decrease immune system function
Vitamin B6plays an important role in
maintain-ing optimal immunity, includmaintain-ing antibody
produc-tion and phagocytic activity Vitamin B6deficiency
impairs the immune system in a number of ways
It lowers cell-directed immune responses,
de-scribed earlier, and leads to decreased thymus
func-tion Vitamin B6 deficiency during gestation in
experimental animals impairs immune functioning
even in first and second generation offspring
ZINChelps maintain lymph glands and the
thy-mus gland, thereby helping to fight chronic
infec-tion Zinc is required for many important enzymes,
and it is not surprising that zinc deficiency
decreases T cell and B cell function and
macro-phage activity However, too much zinc can depress
immunity Zinc, in combination with other trace
minerals including copper, iron, and manganese,
appears to improve B and T cell function in older
people
Copper deficiency is associated with an
increased risk of infection Copper deficiency
diminishes the effectiveness of the humoral system
in lab animals Copper is an essential component of
SUPEROXIDE DISMUTASE, an antioxidant system, and
CYTOCHROMEC oxidase, an enzyme system required
for energy production
Immunity, Stress, and Exercise
Physical or emotional stress can alter hormonal
output and immune response A high level of stress
increases the risk of illness and injury in the
fol-lowing year and shortens the life span
Emotional well-being is supported by proper
diet and regular physical EXERCISE Moderately
intense exercise increases the production of ENDOR
-PHINS, the brain’s own opiates, which can bolster
parts of the immune system Studies indicate that
interleukin-1 and interferon, which help the body respond to infection or injury, increase after mod-erate exercise Modmod-erate exercise also increases killer cell activity
Strenuous aerobic exercise may decrease effi-ciency of the immune system and temporarily increase susceptibility to illness by increasing the production of adrenal stress hormones Among the hormones produced is cortisol, which limits inflammation by blocking the immune system With continued stress, production of protective antibodies (such as secreted IgA, the antibody that protects the intestine and other body cavities against invasion by foreign substances) Chronic stress also decreases killer cell activity, increasing a person’s susceptibility to disease (See also AGING; B COMPLEX; ENDOCRINE SYSTEM; MALNUTRITION; NER
-VOUS SYSTEM; PSYCHONEUROIMMUNOLOGY.) Chandra, R K “Nutrition and the Immune System from
Birth to Old Age,” European Journal of Clinical Nutrition
56, supp 3 (August 2002): 573–576.
inborn errors of metabolism Abnormal gene products can cause metabolic imbalances, resulting
in disease Generally the inherited defect leads to the inadequate formation of an enzyme Occasion-ally, inadequate formation of a COENZYME(enzyme helper) limits enzyme function or the protein-based signalling system that regulates a given enzyme’s function Most genetic defects are classi-fied as autosomal recessive, meaning that they are not sex-linked Full expression of the imbalance can occur only when both chromosomes contain the defective gene coding for a given enzyme and normal genes coding for that enzyme are absent Examples of genetic diseases related to nutrients include familial HYPERCHOLESTEROLEMIA(high blood
CHOLESTEROL), sickle cell anemia, GALACTOSEMIA, and PHENYLKETONURIA PKU is an inherited inability
to metabolize the essential AMINO ACID, PHENYLALA
-NINE PKU responds to nutritional intervention During infancy and childhood PKU patients receive carefully balanced diets that provide only enough phenylalanine to support growth Labels for foods containing the artificial sweetener ASPARTAME
must warn phenylketonurics because of its pheny-lalanine content (See also DNA; FOOD LABELING;
MUTATION.)
inborn errors of metabolism 361
Trang 7Brusilow, S W., and N E Maestri “Urea Cycle Disorders:
Diagnosis, Pathophysiology and Therapy,” Advances in
Pediatrics 43 (1996): 127–170.
indigestion See GASTROINTESTINAL DISORDERS
individuality See BIOCHEMICAL INDIVIDUALITY
induction The increased production of an
ENZYME in response to external stimuli Enzymes
function as biological catalysts of cellular chemical
reactions The body can adapt to a limited extent to
changes in the diet and to environmental
influ-ences by altering the levels of enzymes in a given
tissue For example, a high-carbohydrate diet leads
to increased production of AMYLASE, the
starch-digesting enzyme of the pancreas Starvation
decreases levels of digestive enzymes and enzymes
responsible for fat and glycogen synthesis but
induces enzymes required for fat and carbohydrate
degradation Enzymes that synthesize BLOOD SUGAR
(glucose) from amino acids are also induced by
starvation
Excessive alcohol consumption induces liver
alcohol oxidizing systems so that alcohol will be
cleared from the blood more efficiently Similarly,
many medications induce liver enzymes
responsi-ble for drug degradation Certain cellular enzyme
levels increase in response to hormones and to
growth promoters Examples include the
hor-mones ESTROGEN (female sex hormone), CORTISOL
(adrenal hormone regulating energy metabolism
and degradation), and GROWTH HORMONE (a
pitu-itary hormone involved both in growth and
main-tenance of tissues, especially muscles) INSULIN
provides the broad impetus for increased enzyme
production in many tissues Insulin from the PAN
-CREAS is perhaps the most general anabolic
hor-mone; that is, it promotes enzymes leading to the
accumulation of protein, fat and carbohydrates
(See also DETOXIFICATION.)
infant formula A manufactured food designed to
nurture the infant during the first year of life, until
weaning Commercial infant formulas are either
nonfat cow’s MILK-based or soybean-based
Com-mon formulas are available in powdered form, as
concentrates, or as ready-to-feed liquid with no
prior preparation No formula exactly reproduces human milk; on the other hand, formulas can pro-vide adequate nutrition for babies
In the late 1970s, production of chloride-deficient formulas caused delayed speech, slowed growth, and poor muscle control in babies who had consumed the products Partially in response to this disaster, Congress passed the Infant Formula Act of 1980, which mandates the U.S FDAto see that this synthetic food meets nutrient standards based upon the American Academy of Pediatrics’ recommendations to assure infant growth and development
In 1982, the FDA adapted quality-control proce-dures to monitor the production of this food As a result, infant formulas are nutritionally similar though not identical to BREAST MILK in total pro-tein, total fat, calcium-to-phosphorus ratio, energy content (calories/100 ml), content of the essential fatty acid linoleic acid, and electrolytes (sodium, potassium, chloride)
There are advantages to infant formulas There
is no limit to the supply, and a mother has greater freedom to care for other children or to return to work Other family members can participate in feeding sessions, developing the warmth of that association The mother of a formula-fed infant can offer the same closeness and stimulation as the
BREAST-FEEDINGmother
In 1998 an estimated 29 percent of women in the United States were breast-feeding their infants
6 months after leaving the hospital Several weeks
of breast-feeding assures that the mother’s antibod-ies will be present in the infant
Cow’s milk formula resembles its source in terms of type of milk protein, total fat, and calcium
to phosphorus ratio It has been adjusted so that the total protein content, carbohydrate, fat, major minerals, linoleic acid, and vitamins are similar to breast milk The La Leche League International does not recommend substituting formula or breast milk with cow’s milk until the baby is a year old or older (eating the equivalent of three baby food jars
of solid food per day) Unprocessed cow’s milk is not a suitable food for infants for many reasons Cow’s milk contains three times as much protein
as human milk, and this protein is more difficult for babies to digest Manufacturers either presoften
or predigest this protein, or they add whey to
362 indigestion
Trang 8adjust the protein ratio Butterfat is also poorly
digested by infants; therefore it is replaced by
veg-etable oils Because the higher concentration of
phosphate and other dissolved minerals in cow’s
milk increases the burden on immature kidneys,
minerals are adjusted to resemble breast milk
Lac-tose or corn syrup solids are used to adjust the
car-bohydrate content Bovine milk protein contains
much more of the essential amino acid
phenylala-nine than human milk protein This situation could
affect infants who cannot tolerate high
phenylala-nine for genetic reasons (see PHENYLKETONURIA)
Cow’s milk in infant formulas sometimes
trig-gers an ALLERGY, especially if there is a family
his-tory of allergies Cow’s milk-based formula as a
supplement to breast-feeding is less of a problem
when the baby is six months or older
For infants who are sensitive to cow’s milk,
liq-uid formulas containing soy protein fortified with
the essential amino acid methionine and with
soy-bean oil are available A variety of formulas are
prepared from coconut oil and corn oil, but these
oils contain very little alpha linolenic acid, an
essential fatty acid Human milk contains
substan-tial amounts of a large fatty acid called DOCOSA
-HEXAENOIC ACID (DHA) DHA, which is necessary
for normal brain and eye development, is not
added to formula There is a consensus that
for-mula should at least contain linolenic acid, the
pre-cursor of DHA, which the infant’s body may
convert to DHA
A wide variety of infant formulas is available to
meet special needs Infants with lactose intolerance
can drink formulas in which lactose is replaced by
other carbohydrates Formulas can be adapted to
adjust protein ratio, linoleic acid content, or to
lower sodium content Special formulas are
avail-able for preterm babies
Ready-to-use formula, as well as powdered
formula, sometimes contains ALUMINUM This is
not a problem for babies with normal kidneys;
however, premature babies may tolerate it poorly
CARRAGEENAN-containing formula should not be
given to premature infants This SEAWEEDproduct is
used to stabilize fat by forming gels in milk
In the past, the infant formula industry
employed questionable marketing practices in
developing countries, which led to a 1977
con-sumer boycott against the Swiss-based Nestlé
com-pany For example, they dressed staff in hospital garb while introducing infant formula to new mothers, and used misleading ads In 1979, Nestlé, which accounted for 50 percent of formula sales to the developing world, and the U.S government formally agreed to voluntary guidelines that banned marketing abuses in developing nations
In 1981, the United Nations World Health Orga-nization voted overwhelmingly to approve an international code of conduct to restrict advertising and marketing of baby formula, which can lead to infant malnutrition and death when improperly used Although not binding, the new guidelines apply to infant formula promotion in industrialized nations as well as developing nations Proper use of infant formula is often impossible in poorer areas
of the world, where the water used to mix the for-mula is often contaminated (See also BABY FOOD.) Ryan, A S “The Resurgence of Breast-feeding in the
United States,” Pediatrics 99, no 4 (1997): e12.
Scariati, Paula D “Risk of Diarrhea Related to Iron Con-tent of Infant Formula: Lack of Evidence to Support the Use of Low-Iron Formula as a Supplement for
Breast-fed Infants,” Pediatrics 99, no 3 (1997): e2.
inflammation A defensive response by the body
to irritation, injury, or infection usually character-ized by heat, redness, swelling, and pain at the injury site This response is triggered by physical agents, chemical agents, or disease-producing organisms Swelling is due to increased blood ves-sel leakage of fluids, and redness is due to the increase in diameter of blood vessels, (especially capillaries) so that they carry more blood With increased vessel leakage, substances normally retained in blood such as water, antibodies, phago-cytic cells, and clot-forming components, migrate into tissues at the site of injury
Cellular Materials that Promote Inflammation
HISTAMINE, kinins, PROSTAGLANDINS, LEUKOTRIENES, and complement contribute to inflammation Hist-amine, derived from the amino acid HISTIDINE, is released from white cells (basophils), mast cells, and other cells when injured Kinins are proteins that induce vasodilation, increase vessel leakiness, attract phagocytic cells, and cause pain Prosta-glandins are hormone-like materials that function
inflammation 363
Trang 9in the immediate area where they are produced.
They play many roles, including intensifying pain
and promoting fever, which helps combat
infec-tions Leukotrienes are extremely powerful
inflam-matory agents Complement is a group of blood
proteins that stimulate histamine release, destroy
bacteria, and promote phagocytosis (engulfing
other cells and fragments) Pain can result from
injured nerves or from irritation by released
micro-bial products Inflammation generates free radicals,
which are highly damaging chemical fragments
Chronic inflammation therefore can produce
cellu-lar damage and oxidative stress, leading to an
unbalanced immune response Many chronic
degenerative diseases involve inflammation and
oxidative damage Examples include rheumatoid
arthritis, atherosclerosis, as well as side effects
resulting from radiation and chemotherapy during
cancer treatment
Nonsteroidal anti-inflammatory drugs (NSAIDS)
are often used to combat inflammation These
drugs, which are often nonprescription items, can
themselves cause damage to the stomach or
intesti-nal lining; in some instances they may harm the
liver when used in excess (See also ASPIRIN;
IMMUNE SYSTEM.)
inflammatory bowel disease (IBD) A chronic
inflammation of the intestinal wall involving
painful swelling and open sores Eventually, the
intestinal wall becomes scarred, which narrows
the intestinal opening IBD affects 1 million to 2
million Americans It differs from CELIAC DISEASE, a
grain (especially wheat) intolerance, and from IRRI
-TABLE BOWEL SYNDROME (spastic colon), a much
more common, less serious condition involving
muscle contractions, rather than chronic
inflam-mation Two distinct disorders are classified as
inflammatory bowel disease: CROHN’S DISEASEand
ulcerative COLITIS Crack-like ulcers and abnormal
granular growths in the intestine often accompany
Crohn’s disease, while ulcerative colitis occurs only
in the large intestine and involves inflammation
and ulceration
IBD symptoms include persistent (sometimes
bloody) DIARRHEA, flatulence, cramps, low-grade
fever, and weight loss, as well as problems such as
ARTHRITISand inflamed eyes or skin Children may
be affected by retarded growth and retarded
sex-ual development IBD increases the risk of colon
CANCER IBD is reported mainly in developed countries, where it is most common between the ages of 12 and 40 The causes of IBD are unknown It does not seem to be caused by stress One theory is that IBD is an AUTOIMMUNE DISEASE in which the per-son’s own immune system attacks the intestine Clearly, immune imbalances seem to play a part Another view is that bacteria, viruses, or toxic chemicals initiate IBD Food sensitivity has also been implicated in some cases
Conventional medical treatment involves drugs and/or surgery Drugs reduce inflammation and can lead to a remission However, steroids have side effects like high blood pressure, diabetes, and thinning of bones Typical treatment recommenda-tions include:
• Eating a well-balanced diet that provides ade-quate nutrients to maintain and repair the intestinal tract It is important to correct any nutrient deficiencies caused by the disease (especially iron, folate, and calcium)
• Eating several small meals throughout the day This may be more effective for good digestion and assimilation than eating three big meals
• Avoiding irritating foods that could increase inflammation These differ from person to per-son, though seeds, nuts and corn, lactose and dairy products, fried or greasy foods, and coffee are often the culprits
• Getting enough exercise and managing stress Severe stress suppresses the immune system and encourages inflammation
• Seeking expert medical advice The National Foundation for Ileitis and Colitis provides important information to patients and their families
Gross, V et al “Free Radicals in Inflammatory Bowel Dis-eases—Pathophysiology and Therapeutic
Implica-tions,” Hepato-Gastroenterology 41 (1994): 320–327.
inhibition Restricting the activity of a cellular or physiologic process Several different mechanisms are involved in inhibition
Hormones Hormones may serve as inhibiting agents because they can inhibit the release of other
364 inflammatory bowel disease
Trang 10hormones Thus, the ovaries produce inhibin (a
hormone that inhibits the secretion of the ovarian
hormones), follicle stimulating hormone, and
lut-enizing hormone, at the end of the menstrual
cycle Elevated CORTISOL from the adrenal glands
inhibits the release of ADRENOCORTICOTROPIN
(ACTH) from the PITUITARY GLAND ACTH stimulates
the release of cortisol
Enzymes Enzymes are protein catalysts that
lose activity when blocked by inhibitors
Competi-tive enzyme inhibitors are compounds that mimic
the chemical that the enzyme usually alters
Enzyme poisons like toxic heavy metals—LEAD,
MERCURY, and CADMIUM—can bind to enzymes
without competing with substances and can
per-manently inactivate enzymes
Certain key regulatory enzymes may be
re-versibly inhibited by the accumulation of key
prod-ucts of metabolism One example is the feedback
inhibition of a METABOLIC PATHWAY, a sequence of
functionally linked enzymes In this type of
inhibi-tion, a surplus of the final product of the pathway
can inhibit the pathway For example, the buildup
of ATP, the energy currency of the cell, can inhibit
enzyme systems like GLYCOLYSISthat generate ATP
Such feedback mechanisms help the cell avoid
wasteful overproduction of products (See also
ENDOCRINE SYSTEM; INDUCTION.)
inosine One of the basic compounds composing
cells and a precursor to adenosine, an important
energy molecule and building block of DNA and
RNA Although some European scientists believed
it could have energy-boosting effects, controlled
studies concluded that inosine does not improve
athletic performance Athletes often take between
5,000 and 6,000 mg of inosine a day, but research
does not support the use of this supplement in any
amount
However, some animal research studies have
suggested it may be helpful in the treatment of
stroke and other central nervous system disorders
Inosine occurs in organ meats and brewer’s yeast
and can be taken as a supplement Although there
are no reports of side effects, any inosine that is not
used by the body is converted to uric acid, which
could be a problem for people at high risk for gout
Safety data are inadequate for pregnant and
breast-feeding women
Starling, R D., T A Trappe, K R Short et al “Effect of Inosine Supplementation on Aerobic and Anaerobic
Cycling Performance,” Medicine and Science in Sports
and Exercise 28 (1996): 1,193–1,198.
inositol (myoinositol) An essential building block of cell membrane LIPIDS Chemically, inositol
is a cyclic ALCOHOLwith six hydroxyl groups, one per carbon atom Inositol is a constituent of phos-phatidylinositol, a component of inner-cell mem-branes Derivatives of inositol function as HORMONE
relay signals in cells Diverse hormones such as
VASOPRESSIN(from the pituitary gland), EPINEPHRINE
(from the adrenal gland) and releasing factors from the HYPOTHALAMUSstimulate the release of inositol triphosphate from phosphatidylinositol
Animal studies show that inositol may protect against ATHEROSCLEROSISand against hair loss Inos-itol is also supposed to help reverse nerve damage caused by diabetes in animals Oral supplementa-tion in human diabetics has not verified this result Diabetics should consult their health care providers before taking inositol supplements Inositol has a low toxicity
Nutritionists have not yet established the opti-mum amount of inositol in the diet It is widely dis-tributed in food and is also manufactured in the body Sources include CITRUS FRUIT (except lemons), CANTALOUPE, whole grain bread, cooked beans, green beans, and nuts Inositol occurs in grains such as PHYTIC ACID, in which six phosphate groups are attached to the inositol molecule Phytic acid can bind minerals and limit their uptake Safety data are inadequate for pregnant and breast-feeding women (See also VITAMIN.)
Shamsuddin, Abulkalaman M “Inositol Phosphates Have
Novel Anti-Cancer Function,” Journal of Nutrition 125,
supp 3 (1995): 725S–732S.
insulin A protein HORMONE, secreted by beta cells
in the PANCREAS, that stimulates the uptake of
BLOOD SUGAR by many tissues Insulin counteracts the effects of GLUCAGON, the pancreatic hormone responsible for raising blood sugar Insulin is used therapeutically to treat DIABETES MELLITUS and is either purified from pork or beef pancreas or is ge-netically engineered of human origin Insulin is produced by small cell clusters in the pancreas
insulin 365