The Encyclopedia Of Nutrition And Good Health - N pot

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451
N-acetylcysteine
(NAC) A derivative of the
sulfur-containing amino acid
CYSTEINE that occurs
naturally in the body, N-acetylcysteine is used to
produce the powerful cell
ANTIOXIDANT GLU-
TATHIONE. This sulfur compound delivers cysteine
to cells. It has been used medicinally to reduce
mucus buildup in people suffering from respiratory
ailments such as chronic bronchitis and asthma,
and adult respiratory distress syndrome. NAC may
help reduce the risk of heart attack in patients with
unstable chest pain. It is also helpful as an IV treat-
ment in ridding the body of toxic levels of the
nonsteroidal anti-inflammatory drug (NSAID)
acetaminophen.
Now also available as a
DIETARY SUPPLEMENT,N-
acetylcysteine is promoted as an aid in boosting the
body’s immune system, preventing heart disease
and cancer and slowing the progression of Parkin-
son’s disease and multiple sclerosis. Initial studies
indicate N-acetylcysteine shows promise in treating
some or all of the conditions. However, additional
research is needed to confirm these preliminary
studies. Because N-acetylcysteine is sold as a
dietary supplement for treating these conditions
and not as a drug, its safety and efficacy has not

been tested by the U.S. Food and Drug Administra-
tion (FDA) or any other government agency.
Breast-feeding women should avoid NAC. Preg-
nant women should use it only with a doctor’s pre-
scription.
Grandjean, E. M., P. Berthet, R. Ruffmann, et al. “Efficacy
of Oral Long-Term N-acetylcysteine in Chronic Bron-
chopulmonary Disease: A Meta-Analysis of Published
Double-Blind, Placebo-Controlled Clinical Trials,”
Clinical Therapy 22 (2000): 209–221.
naphthoquinone See
VITAMIN K.
narcotics See
ADDICTION.
National Cholesterol Education Program See
CHOLESTEROL.
National Marine Fisheries Service Organization
that is part of the National Oceanic and Atmos-
pheric Association (NOAA), responsible for over-
seeing fisheries management in the United States.
Under the federal Agricultural Marketing Act of
1946, NOAA administers a voluntary Seafood
Inspection Program to ensure that seafood sold in
the United States complies with applicable food
regulations, including the Hazard Analysis and
Critical Control Point (HACCP, pronounced “has-
sip”) regulations implemented by the U.S. Food
and Drug Administration (FDA) in 1997. This pro-
gram requires seafood processors, repackers, and
warehouses that supply seafood for sale in the

United States to have in place a food safety pro-
gram to identify and eliminate sources of food-
borne illnesses. The aim of the HACCP system is to
prevent problems before they start by conducting
spot checks of manufacturing processes and ran-
dom testing of seafood products. Retailers are
exempt from HACCP requirements.
National Research Council (NRC) The branch
of the National Academy of Sciences promotes the
effective use of scientific information and advises
the federal government on scientific and technical
matters. The NRC provides services for following
policies set by both the National Academy of Sci-
ences and the National Academy of Engineering in
meeting the needs of government, the public, and
scientists. It is administered by these academies, as
well as by the Institute of Medicine.
Among the many responsibilities of the NRC is
the development and evaluation of nutrient stan-
dards for good health. In 1941, the Food and
Nutrition Board of the NRC published the Recom-
mended Dietary Allowances (RDAs), the bench-
mark of nutritional adequacy in the United States,
with revised editions generally appearing every
five years. The 10th edition was published in 1989.
Since then the Food and Nutrition Board, in coop-
eration with Health Canada, has been gradually
replacing the RDAs with
DIETARY REFERENCE INTAKES
(DRIs), which incorporate more recent science that

has broadened our understanding of the role of
nutrients in human health. (See also
DIETARY
GUIDELINES FOR AMERICANS
; NUTRIENT; VITAMIN.)
National School Lunch Program See SCHOOL
LUNCH PROGRAM
.
natural flavors See FLAVORS.
natural food Foods that have been minimally
processed and grown without the use of synthetic
fertilizers and pesticides. Other than for meat and
poultry, the term natural has not been defined
legally and therefore has many interpretations. The
“natural” food label is a strong selling point, and
food producers have capitalized on consumer inter-
est. Thus the word natural may be used to describe
PROCESSED FOODS and synthetic food and beverages,
which sometimes are highly processed and contain
preservatives and artificial coloring. A beverage
labeled “natural” might be completely synthetic,
with only the lemon flavor as a nonsynthetic ingre-
dient; a product labeled “Natural Juice Apple Pie”
may indicate only the juice is natural. Natural food
also has the connotation of being free from addi-
tives like
PRESERVATIVES, EMULSIFIERS, and thicken-
ers. Under current U.S.
FDA regulations, an entire
food cannot be labeled natural if it contains syn-

thetic ingredients,
ARTIFICIAL FLAVORS, or ARTIFICIAL
FOOD COLORS
.
Natural Meat
According to the
USDA, MEAT or poultry labeled
“natural” has not been processed more than in
usual kitchen practice. This refers to procedures
that can be performed in the kitchen: washing,
shredding, chipping, grating, grinding, chopping,
mixing, and cooking. Natural meat must come
from animals raised without hormones or at least
not exposed to feedlot growth stimulants (such as
antibiotics) to fatten livestock later than 60 days
before slaughter. The “natural beef” label doesn’t
guarantee the meat is absolutely free of antibiotics
and growth factors because some producers feed
hormones and antibiotics up to 60 days before
slaughter. This time may be inadequate to com-
pletely clear chemical residues from some animals.
(See also
FOOD ADDITIVES; ORGANIC FOODS
.)
natural sweeteners Naturally occurring
CARBO-
HYDRATES or compounds related to SUGARS that are
used as sweeteners. Carbohydrate sweeteners con-
tribute four
CALORIES per gram (less than half as

much as fat). The most common are the simple
sugars or materials that are primarily sugars:
FRUC-
TOSE and high fructose corn syrup; GLUCOSE
(known in the food industry as DEXTROSE); CORN
SYRUP
; various forms of SUCROSE, including
MOLASSES, brown sugar, table sugar, turbinado
sugar, and cane sugar;
BARLEY MALT; HONEY; fruit
concentrates; and ground dates (date sugar).
Amasake is a sweetener prepared from fermented
rice. Each provides carbohydrate with only a few
other nutrients; therefore the content of
VITAMINS,
minerals, and
FIBER, as compared to that found in
whole foods, is low (
EMPTY CALORIES).
Sugar alcohols taste sweet and are not as easily
metabolized as sugars.
MANNITOL, related to the
sugar mannose, is poorly utilized.
XYLITOL, derived
from the sugar xylose, while degraded, contributes
fewer calories than sugar.
SORBITOL, related to sor-
bose, is the most widely used sugar alcohol and is
only slowly absorbed by the intestine. Relative to
table sugar, fructose is 1.7 times as sweet; glucose,

0.7; mannitol, 0.7; and sorbitol, 0.6.
Potential Problems with
High Sugar Consumption
Undernutrition Sugars supply empty calories
because they provide low or negligible amounts of
key nutrients.
CARBOHYDRATE METABOLISM requires
B vitamins like
THIAMIN and minerals like ZINC,
CHROMIUM, and MAGNESIUM. Excessive concen-
trated sweeteners displace more nutritious food
452 National School Lunch Program
and increase the body’s burden for these nutrients.
Few people relying on a junk food diet increase
their consumption of high-quality foods to make
up the difference.
Overnutrition Excessive consumption of sugar
and refined carbohydrate represents excessive calo-
ries. Surplus calories are converted to
FAT, regard-
less of their source. It should be noted that starches
and sugars are not in themselves inherently fatten-
ing unless they represent excess calories.
Blood Sugar Imbalances The excessive con-
sumption of simple sugars and sucrose can cause
BLOOD SUGAR
levels to fluctuate. In contrast,
STARCHES in vegetables and legumes are often
slowly digested and glucose is absorbed slowly, per-
mitting a more balanced control of blood sugar.

Cavities Excessive sugar consumption leads to
more cavities and contributes to soaring dental costs.
U.S. DIETARY GUIDELINES FOR AMERICANS call for
eating less sugar and more complex carbohydrate,
starch, and fiber (whole foods) as vegetables, fruits,
and legumes. The
FOOD GUIDE PYRAMID, the most
recent meal planning guideline, specifies eating
sweets sparingly. (See also
ADDICTION AND SUGAR;
INVERT SUGAR; MAPLE SYRUP; NUTRIENT DENSITY; TEETH.)
Anderson, G. H. “Sugars, Sweetness and Food Intake,”
American Journal of Clinical Nutrition 62, supp. 1
(1995): 195S–202S.
Wolever, T. M., and J. B. Miller. “Sugars and Blood Glu-
cose Control,” American Journal of Clinical Nutrition 62,
supp. 1 (1995): 212S–221S.
natural vitamins See VITAMIN.
nectar A FRUIT drink made with fruit juice and
fruit pulp. Typical nectars are made from
APRICOT,
GUAVA, MANGO, PEACH, and other fruit. Ingredients
are specified by the
STANDARDS OF IDENTITY estab-
lished by the U.S.
FDA. These are standard recipes
long used by the food industry. Nectars include var-
ious combinations of fruit juice, SUGAR, and other
natural sweeteners, together with fruit puree, fruit
pulp,

VITAMIN C, and CITRIC ACID. The term nectar
also refers to a sweet, syrupy fluid secreted by flow-
ers and collected by bees to produce HONEY.
nectarine (Prunus persica) A subspecies of PEACH
with a smooth skin and a distinctive flavor. The
close similarity between nectarines and peaches is
demonstrated by the fact that nectarines occasion-
ally mutate to peaches and vice versa. Nectarines
and peaches are believed to have originated in
China. There are more than 150 varieties of nec-
tarine, differing slightly in taste, shape, size, and
skin coloring. Fantasia, Summer Grand, Royal
Giant and May Grand are popular varieties. The
United States is a major producer, and California
produces most of the domestic crop. Hard nec-
tarines can be softened by storing them in a paper
bag at room temperature for several days. The
mature fruit does not get very much sweeter, but it
can become softer and juicier.
Nutrient contents of one raw nectarine, without
pit, is 67 calories; protein, 1.3 g; carbohydrate, 16 g;
fiber, 3.13 g; fat, 0.6 g; potassium, 288 mg; vitamin
A, 100 retinol equivalents; vitamin C, 7 mg; thiamin,
0.02 mg; riboflavin, 0.06 mg; niacin, 1.35 mg.
nephron The functional unit of kidneys that fil-
ters the blood. The nephron further modifies fil-
tered fluid from the blood to produce urine.
Nephrons are composed of two structures: renal
tubules and the glomerulus, a cluster of
CAPILLAR-

IES. WATER
, MINERALS
, GLUCOSE, VITAMINS, AMINO
ACIDS
, very small proteins, nitrogenous wastes, and
small molecules migrate from the capillaries of the
glomerulus and enter the renal tubule, which
draws urine from the kidneys.
As the filtrate moves down the tubules, nearly
99 percent of the water is reabsorbed into the
blood. Only 1.5 liters (1 percent leaves as urine
daily. By reabsorbing most of the materials, the
body can retain essential nutrients, while disposing
of wastes like
UREA. For example, normally all of
the glucose filtered by the glomerulus is reab-
sorbed, thus, maintaining blood glucose levels. So
much liquid is filtered by the kidney that if nutri-
ents were not reabsorbed back into the blood-
stream, the blood would be drained of these
materials within half an hour.
The region of the tubule adjacent to the capsule
(proximal tubule) reabsorbs glucose, amino acids,
SODIUM, CHLORIDE, BICARBONATE, POTASSIUM, and
water. Farther down the tubule, sodium, chloride,
urea, and water are reabsorbed. Sodium and water
are controlled by the hormone
ALDOSTERONE. The
nephron 453
kidney releases potassium and AMMONIA to main-

tain
ELECTROLYTE balance and water balance of the
blood. In order to maintain blood pH close to 7.4
(neutral pH) and to maintain acid-base balance,
sodium is reabsorbed while hydrogen ions are
released.
The kidney plays a role in
VITAMIN D metabolism
as well. Tubules of the kidney activate vitamin D by
converting a partially modified form (called
hydroxycholecalciferol) to the fully active hor-
mone, called calciferol. (See also
GLOMERULAR FIL-
TRATION
.)
nervous system A primary communication sys-
tem consisting of the brain, spinal cord, and nerve
fibers radiating to all parts of the body. The brain
and spinal cord occupy a central position in the
body and are called the “central nervous system”
(CNS). The nervous system transmits information
via electrical nerve impulses conducted between
nerve cells. Impulses are generated by changes in
the body’s internal or external environment.
Specialized cells of the nervous system are called
neurons and neuroglia. Neuroglia are connective
tissue cells supporting the neurons, while neurons
are specialized cells of the nervous system that con-
duct nerve impulses. The nervous system is com-
posed of billions of neurons. With age, neurons are

progressively and irreversibly lost.
Sensory neurons transmit impulses to the spinal
cord and brain from all regions of the body, while
motoneurons transmit impulses away from the
brain and spinal cord to muscles and glands.
Interneurons lie within the gray matter of either
the brain or spinal cord and conduct impulses from
sensory neurons to motoneurons. A fatty layer
called
MYELIN insulates nerve fibers, bundles of
neurons.
Neurons contain a cell body with nucleus,
CYTO-
PLASM and MITOCHONDRIA. Each neuron possesses
many dendrites, highly branched extensions of the
cell body that are the “receiving” parts of neurons
and conduct a nerve impulse toward the cell body;
and an AXON, a single, long cytoplasmic extension
that conducts nerve impulses away from the cell
body to another cell. Axons contain mitochondria
but no protein synthesizing machinery; they vary
in length from a few millimeters up to a meter or
more. The ends of axons terminate in bulb-like
structures that store
NEUROTRANSMITTERS. These
chemicals determine whether an impulse will pass
onto the next cell. Nerve fiber refers to any process
projecting from the cell body. Typically, sensory
neurons transmit impulses from the skin, sense
organs, muscle joints and viscera to the spinal cord

and the brain. Motoneurons convey impulses from
the brain and spinal cord to either muscles or
glands. Connecting neurons (intraneurons) carry
impulses from sensory neurons to motor neurons
and occur in the brain and spinal cord.
Many nutrients support nerve function, and the
following minerals are critical.
CALCIUM is required
for nerve transmission; when blood calcium levels
fall, nerves become hypersensitive, and the result
is frozen muscles (tetany). High calcium concen-
trations depress nerve irritability. The amount of
neurotransmitters (serotonin, acetylcholine, nor-
epinephrine) released is proportional to the cal-
cium concentration in the nerve terminus.
POTASSIUM and SODIUM are important in nerve
transmission. Stimulation of a nerve causes potas-
sium to migrate out of the neuron and sodium to
migrate inward, altering the membrane potential
(electrical current) and conducting a nerve impulse
down the axon.
Individual nerve cells communicate at special-
ized gaps called synapses by means of chemical
messages called neurotransmitters. When a nerve
impulse reaches the end of an axon it triggers the
release of neurotransmitters that migrate across the
gap and stimulate a nerve impulse or other
response in the receiving cell. Neurotransmitters
are often derived from
AMINO ACIDS. Dopamine

and norepinephrine are derived from the amino
acid
TYROSINE, while TRYPTOPHAN supplies SERO-
TONIN. Cholinergic nerve fibers release the neuro-
transmitter
ACETYLCHOLINE and are derived from
the nitrogen-containing nutrient
CHOLINE.
The peripheral nervous system contains sensory
nerves. These carry information from organs like
the skin to the brain. Motor nerve fibers carry
impulses from the brain to specific regions such as
skeletal muscles.
The automatic nervous system adapts the body
to change. It consists of two functional parts. The
sympathetic nervous system responds to stress,
454 nervous system
and adaptations include dilation of bronchi and
increased heart rate. The
PARASYMPATHETIC NERVOUS
SYSTEM
returns the body to the normal, unstressed
state, counterbalancing the sympathetic nervous
system. It restores energy during rest and recupera-
tion.
The average human brain weighs about three
lbs (1.4 kg) and contains 11 billion cells. Although
it represents only 2 percent of the total body
weight, it consumes 20 percent to 30 percent of the
GLUCOSE

from digestion and CARBOHYDRATE METAB-
OLISM. The thalamus of the forebrain is an egg-
shaped mass that relays sensory information to
other regions of the brain. It seems to help with
concentration. Lying beneath the thalamus is the
HYPOTHALAMUS, which regulates eating, drinking,
sexual behavior, heat production, and emotions. It
also controls the
ENDOCRINE SYSTEM
, a system of
hormone-secreting glands located throughout the
body.
Twelve pairs of nerves are attached at the under
surface of the brain. Several are important in regu-
lating eating and digestion. Their fibers conduct
pulses between the brain and the head, neck, tho-
rax, and abdominal cavity. The olfactory nerve is
responsible for the sense of
SMELL. The trigeminal
nerve functions in the sensations involving the
face, teeth, and chewing. The facial nerve is
responsible for
TASTE. The glossopharyngeal nerve
controls taste, swallowing, salivation, and sensa-
tions in the throat region. The vagus nerve also
regulates swallowing, sensations of throat and lar-
ynx, and of the abdominal regions; for example, it
regulates
PERISTALSIS. The hypoglossal nerve regu-
lates tongue movements (swallowing).

It is now known that brain peptides, such as
ENDORPHINS, are synthesized in the intestine, while
hormones bind to targets in the brain and affect its
function. The nervous system can activate the
immune system, while chemicals released by the
immune response can affect the central nervous
system. The gastrointestinal tract is surrounded by
an elaborate network of nerves so that the stomach
and intestines are directly linked to the brain. The
ability of the digestive system to monitor food has
important ramifications for
WEIGHT MANAGEMENT,
SATIETY, and hunger. With the discovery that the
hormonal system (endocrine system) as well as the
immune system can affect the brain and alter
behavior and mood, and that the nervous system
can alter the immune response and hormone bal-
ance, has come a new appreciation of the interde-
pendency of these three systems in maintaining a
balance among all systems of the body (
HOMEOSTA-
SIS). This synthesis has spawned a new scientific
discipline, psychoneuroimmunology.
In addition to supplying energy, primarily as
glucose, food can alter the nervous system in
important ways. One focus has been in the forma-
tion of neurotransmitters, chemicals manufactured
by nerves to help transit nerve impulses. Two
amino acids that serve as the raw materials for the
manufacture of neurotransmitters are tryptophan

and tyrosine. Tryptophan forms the neurotransmit-
ter serotonin, used to regulate relaxation and
sleepiness. Low blood levels of tryptophan are
linked to depression, and some clinical studies sug-
gest that tryptophan supplementation can lessen
depression. Tryptophan tends to make normal peo-
ple drowsy, and it has been sold as a mild sleep
inducer. However, the U.S.
FDA has banned its sale
because of deaths associated with contaminated
tryptophan. Foods low in protein and rich in car-
bohydrate can raise brain levels of tryptophan,
probably because they stimulate the release of
insulin, which lowers the blood levels of most
amino acids, except for tryptophan. According to
one hypothesis, tryptophan in the blood competes
with more abundant, branched chain amino acids,
which also possess lipid-like properties, for entry
into the brain. The amount of tryptophan reaching
the brain increases after eating starchy or sweet
foods. On the other hand the more numerous
amino acids can displace tryptophan for entry into
the brain after eating a protein-rich meal. As a
result, brain tryptophan levels may drop. The
observation is that normal healthy adults can feel
relaxed, sleepy, or more calm or lethargic within
two hours following a high-carbohydrate meal.
Another possibility is that glucose from carbohy-
drate digestion can affect the brain’s activity.
The amino acid tyrosine is converted to the

neurotransmitter norepinephrine, which helps
maintain mental alertness. The brain level of norep-
inephrine drops with stress. Tyrosine supplements
may help combat fatigue and improve the ability to
nervous system 455
perform mental tasks. A light lunch or snack
increases mental functioning and decreases the
error rate in tasks, and seems to sharpen the mind.
Certain B vitamins help in the manufacture of
serotonin and norepinephrine:
VITAMIN B
6
, VITAMIN
B
12
, and
FOLIC ACID. Deficiencies of any of these vit-
amins can promote depression, senility, and
decreased ability to concentrate. Correction of the
B vitamin deficiency can ease these symptoms.
Even in healthy elderly people without obvious
deficiency symptoms, a lower level of folacin and
vitamin B
12
has corresponded to lower scores on
reasoning tests. Surveys have shown that between
20 percent and 66 percent of healthy people over
the age of 65 possess low levels of vitamin B
6
, vit-

amin B
12
, and folic acid. (See also ADDICTION; DIGES-
TIVE TRACT; FOOD AND THE NERVOUS SYSTEM; MOUTH.)
Duthie, S. J. et al. “Homocystine, Vitamin B Status, and
Cognitive Function in the Elderly,” American Journal of
Clinical Nutrition 75, no. 5 (2002): 908–913.
net protein utilization (NPU) An index used to
estimate the ability of a food
PROTEIN to supply
indispensable
AMINO ACIDS. Only retained nitrogen
is measured. The NPU is based on the ratio of the
amount of dietary protein converted to body pro-
tein divided by the amount of protein eaten. Thus,
a poorly digested protein would have a low NPU
score. In this respect, it differs from the
BIOLOGICAL
VALU E
, which does not account for digestibility of
food. Frequently, proteins are measured for their
growth-promoting effect on young animals or for
their ability to maintain nitrogen equilibrium, a
balance between protein nitrogen consumed and
the amount lost daily (
NITROGEN BALANCE). Since
only retained nitrogen is measured, NPU does not
specifically assess the inefficiency of digestion.
Thus, a poorly digested protein would have a low
NPU score. (See also

CHEMICAL SCORE.)
neural tube defects
(NTD) Congenital disorders
related to the incomplete development of the
neural tube. Neural tube defects contribute to
infant mortality throughout the world. Anen-
cephalus is the absence of brain and spinal cord. In
spina bifida, the spinal cord is pushed through the
wall of the spinal canal between vertebrae.
Encephalocele refers to the protrusion of the brain
through a cranial opening. Both genetic and envi-
ronmental factors are implicated. Several studies
have confirmed that women who take the B vita-
min
FOLIC ACID before becoming pregnant and dur-
ing the first two months of pregnancy greatly
reduce the risk of bearing a child with a neural tube
defect. Consequently, the Centers for Disease Con-
trol and Prevention (CDC) recommends that all
women of childbearing age take a multivitamin
that contains at least 400 mcg of folic acid daily. In
1998 the U.S.
FDA began requiring all enriched
grain products, including cereals, breads, pasta, and
rice, to be fortified with folic acid at the rate of 140
mcg per 100 g of grain. This action was taken based
on studies that showed that only about 25 percent
of women of childbearing age in the United States
regularly consumed enough folic acid. In 2001 the
CDC reported that the number of children born

with these defects had dropped by 19 percent since
the enrichment program began. (See also
BIRTH
DEFECTS
; HOMOCYSTEINE; VITAMIN.)
Honein, Margaret A. “Impact of Folic Acid Fortification in
the U.S. Food Supply on the Occurrence of Neural
Tube Defects,” JAMA 285 (2001): 2,981–2,986.
neuron See NERVOUS SYSTEM.
neuropathy, peripheral Disease of the peripheral
nerves (the nerves feeding into the spinal column
and brain). Nutritional deficiencies can cause
peripheral nerve degeneration. Severe deficiency
of the B vitamin
THIAMIN, a disease whose chief
characteristic is
BERIBERI, also leads to neuropathy.
Certain toxic chemicals like plasticizers and several
medications such as Isoniazid also cause neuropa-
thy. Diseases affecting the entire body like diabetes,
certain
AUTOIMMUNE DISEASES like Guillain-Barre
syndrome, and a variety of rare hereditary diseases
are associated with peripheral neuropathy. Neu-
ropathy can be caused by
HEPATITIS, infectious
mononucleosis,
ALCOHOLISM, and lead poisoning.
(See also
DEFICIENCY DISEASE; HEAVY METALS; NER-

VOUS SYSTEM.)
McLeod, J. G. “Investigation of Peripheral Neuropathy,”
Journal of Neurological and Neurosurgical Psychiatry 58
(1995): 274–283.
456 net protein utilization
neurotransmitter A chemical required to transmit
nerve impulses between nerve cells. Unlike an elec-
trical network, nerves are not continuous; the end
of a nerve cell does not touch its target. Instead,
individual nerve cells are separated by a microscopic
gap called a synapse. In response to a nerve impulse
traveling down the nerve cell, the nerve ending
releases neurotransmitter molecules, which then
diffuse across the gap and bind to the adjacent cell.
Depending on the nature of the receiving cells, this
contact can stimulate or inhibit the target cell.
At least three classes of neurotransmitters
respond to diet: Catecholamines (
DOPAMINE and
norepinephrine) come from the
AMINO ACID, TYRO-
SINE. Eating a protein-rich meal can increase blood
tyrosine levels and increase levels of this amino
acid in the brain. Elevated brain tyrosine increases
dopamine and norepinephrine production, pro-
moting wakefulness and alertness.
On the other hand,
SEROTONIN tends to induce
relaxation and sleep. Serotonin comes from the
essential amino acid-

TRYPTOPHAN. Eating a meal
high in carbohydrates is believed to increase indi-
rectly brain tryptophan levels. Elevated blood sugar
stimulates insulin release; this hormone stimulates
the uptake by muscle of amino acids that compete
with tryptophan for uptake by the brain, allowing
more tryptophan into the brain. This in turn leads
to higher serotonin formation in the brain, pro-
moting a state of relaxation. Amino acid research
in humans is still considered preliminary.
ACETYLCHOLINE is manufactured from CHOLINE,a
nitrogen-containing nutrient and raw material for
neurotransmitter synthesis. The body can synthe-
size choline, and it comes also from dietary lipids,
particularly
LECITHIN, a common phosphate-bearing
lipid found in most foods. Acetylcholine partici-
pates in many brain functions, including memory.
Victims of
ALZHEIMER’S DISEASE have low levels of
acetylcholine in their brains. (See also
ENDORPHINS;
NERVOUS SYSTEM.)
neutral fats See FAT; VEGETABLE OIL.
NHANES (National Health and Nutrition Examina-
tion Survey) In 1956 Congress passed the
National Health Survey Act, which authorized the
federal government to conduct a continuing survey
that would produce statistics on the amount, distri-
bution, and effects of illness and disability in the

United States. During the next decades nutrition
began to play a greater role in the understanding of
sickness and disability.
In 1970 a special task force reporting to the
Department of Health, Education, and Welfare rec-
ommended that future surveys include clinical
observation and professional assessment as well as
recording of dietary intake patterns. Since then the
U.S. Center for Health Statistics has been conduct-
ing regular National Health and Nutrition Exami-
nation Surveys.
NHANES I provided statistics between 1971 and
1975; NHANES II between 1976 and 1980; and
NHANES III between 1988 and 1994. A Hispanic
Health and Nutrition Examination survey was con-
ducted from 1982 to 1984.
Since 1999 NHANES has been conducted annu-
ally. Beginning in 2002 it merged with the U.S.
Department of Agriculture’s Continuing Survey of
Food Intakes (CSFII), to produce the National Food
and Nutrition Survey (NFNS). This integrated sur-
vey provides comprehensive information on the
health and nutrition intakes of the U.S. population.
(See also
EATING PATTERNS
.)
Kleges, R. C., L. H. Eck, and J. W. Ray. “Who Underre-
ports Dietary Intake in Dietary Recall? Evidence from
the Second National Health and Nutrition Examina-
tion Survey,” Journal of Consultative and Clinical Psychol-

ogy 63, no. 3 (1995): 438–444.
niacin (nicotinic acid, vitamin B
3
) A heat-stable
member of the B
VITAMIN complex needed by the
body to extract
ENERGY from FAT, CARBOHYDRATE,
and
PROTEIN. Tissues convert niacin to two closely
related
COENZYMES (enzyme helpers): NICOTINAMIDE
ADENINE DINUCLEOTIDE
(NAD) and nicotinamide
adenine dinucleotide phosphate (NADP). NAD
functions as an oxidizing agent used in processes
that “burn” fuels to produce energy in the cell.
These include the oxidation of
GLUCOSE (GLYCOLYSIS)
and of
FATTY ACIDS. NAD transfers electrons to the
mitochondrial
ELECTRON TRANSPORT CHAIN, which
ultimately reduces
OXYGEN to water. This process
liberates vast amounts of chemical energy trapped
as
ATP as well as releasing heat. NADP is generated
from the oxidation of glucose (pentose phosphate
niacin 457

pathway). The reduced form of NADP, NADPH, is
used as a reducing agent in biosynthetic reactions
rather than for energy production.
CHOLESTEROL,
fatty acids, and other important compounds require
NADPH for their synthesis. NADPH is also the basis
of a powerful antioxidant system (
GLUTATHIONE) to
protect most cells from the damaging effects of
highly reactive molecules called
FREE RADICALS.
NADPH also functions in the synthesis of
DEOXYRI-
BOSE, the sugar building block of DNA.
Possible Roles of Niacin in Disease
PELLAGRA
is a severe niacin deficiency disease that
mimics schizophrenia. Skin rashes,
DIARRHEA, and
mouth sores are prevalent in pellagra. At the turn
of the century, pellagra was epidemic in the south-
ern United States among people whose diet was
based on corn. By 1937, research demonstrated
that niacin cured pellagra-like symptoms in dogs
and, shortly thereafter, that niacin treatment cured
pellagra. Niacin has been used in food fortification
since 1941.
Niacin is effective in the treatment of elevated
(hyperlipidemia) blood lipids that does not respond
to dietary intervention alone, and it has been

approved by the USFDA for this treatment. It may
also reduce the risk of a second heart attack in men.
Niacin is effective in lowering high blood triglyc-
erides and elevated LDL-cholesterol, the “bad”
form, and raising HDL-cholesterol, the beneficial
form. Niacin is generally considered an adjunct
therapy, used in conjunction with cholesterol-
lowering drugs, such as statins and bile binding
resins. As an example, niacin in combination with
bile-binding agents may effectively slow the pro-
gression of atherosclerosis in men with existing car-
diovascular disease.
The use of niacin to treat schizophrenia and
DEPRESSION is controversial. Generally negative
results have been reported for patients with long-
standing schizophrenia. Some clinicians reported
improvement in patients with schizophrenia using
megavitamin treatment with niacin or niaci-
namide,
VITAMIN B
6
and VITAMIN C and in patients
with depression using niacinamide and trypto-
phan, together with taking steps to improve the
diet. The American Psychological Association dis-
approved the use of niacin in the treatment of
mental disorders in 1979.
Niacin when taken in combination with choles-
terol-lowering “statin” drugs may prevent
HEART

ATTACKS
.
Niacin seems to increase the production of
PROSTAGLANDINS. These hormone-like chemicals are
produced locally within tissues to help control
many physiologic processes such as
BLOOD CLOTTING
and INFLAMMATION.
Large doses of niacin may alleviate noninflam-
matory
ARTHRITIS, while low doses of niacin can
relieve migraine headaches. Niacin supplements
may help normalize blood sugar in patients with
hypoglycemia. Large doses of niacin may prevent
harmful effects of chemical pollutants, drugs, and
alcohol, and may help during recovery and drug
rehabilitation (the mechanism is not known). This
is a promising area of research, but niacin cannot
be claimed to be a broad-spectrum detoxification
agent.
Sources
Good sources of niacin are
EGGS, MEAT (especially
liver), fish,
POULTRY, and unprocessed food, includ-
ing peanuts and potatoes.
COFFEE provides about 3
mg per cup. Niacin is one of the commonly fortified
nutrients; consequently, enriched flour and cereals
are good sources.

MILK and CHEESE are good sources
because they contain large amounts of the essential
AMINO ACID
, TRYPTOPHAN, which is partially con-
verted by the body to niacin. Protein-deficient diets
are often related to pellagra. This explains why diets
incorporating milk can prevent or cure pellagra.
The form available from animal foods is
NIACI-
NAMIDE, a derivative of niacin; plant foods provide
niacin itself. Niacin is one of the most stable of the
B vitamins: It resists most cooking procedures and
can be stored in the dry state indefinitely without
loss. Canning,
DEHYDRATION, and exposure to air or
light cause little destruction.
Up to 70 percent of the niacin in most cereal
grains, including corn, is present as a bound form
called niacytin. It is not released during digestion
and therefore is poorly absorbed. Traditionally,
corn tortillas are prepared from corn pretreated
with lime water to improve dough consistency, a
treatment that also frees niacin. Pellagra is uncom-
mon in Mexico, Central America, and South Amer-
ica, where corn is soaked in lime. Niacin deficiency
and pellagra are common only in certain regions of
458 niacin
Africa and Asia, where corn is a major source of
protein. Because niacin is so prevalent in high-
quality protein, only alcoholics and heavy drinkers

are likely to be deficient in the United States.
Symptoms of mild deficiency include apathy,
headache, irritability, and memory loss.
Requirements
The
RECOMMENDED DIETARY ALLOWANCE for health
adult men is 19 mg; for nonpregnant, nonlactating
women it is 15 mg. The daily niacin requirement
varies with the number of calories burned daily
(the energy expenditure) and the protein intake.
One niacin equivalent equals 1 mg of preformed
niacin or 60 mg of dietary tryptophan.
Niacin can be synthesized in the body from the
essential amino acid tryptophan. Tissues can form
an average of 1 mg of niacin from 60 mg of trypto-
phan provided by dietary protein. Consequently, a
high-quality protein diet supplies substantial tryp-
tophan for niacin synthesis. On the other hand, a
protein-deficient diet or a diet relying on low tryp-
tophan protein increases the dietary requirement
for niacin. Most animal protein contains 1.4 per-
cent tryptophan; vegetable protein, 1 percent; and
corn protein, only 0.6 percent.
Safety
Niacin (but not closely related niacinamide)
expands
CAPILLARIES and can lead to itching and
flushing at doses commonly used in multivitamin
supplements (100 mg or more). While nausea, diar-
rhea, and flushing may accompany niacin usage,

these side effects are not considered dangerous.
Excessive niacin can cause irregular heartbeat,
cramps, headache, and liver inflammation. “Sus-
tained release” niacin may cause less flushing, but
some preparations may be more toxic to the liver.
Other forms, such as inositol hexaniacinate, may
improve niacin therapy. Large doses of niacin can
increase
BLOOD SUGAR in diabetics, increase the risk
of
GOUT, and aggravate ulcers. Niacin supplements
are not recommended for those with
PEPTIC ULCERS,
COLITIS, ASTHMA, liver disease, GOUT, or erratic heart-
beat. Using niacin therapeutically (1,000 mg or
more per day) requires medical supervision; liver
function and blood sugar need to be monitored.
(See also
CARBOHYDRATE METABOLISM; CHOLESTEROL-
LOWERING DRUGS; FAT METABOLISM; FORTIFICATION.)
Brown, B. G. et al. “Simvastatin and Niacin, Antioxidant
Vitamins, or the Combination for the Prevention of
Coronary Disease,” New England Journal of Medicine
345, no. 22 (2001): 1,583–1,592.
niacinamide (nicotinamide) A derivative of the
water-soluble vitamin
NIACIN. Niacinamide is read-
ily formed in the body from niacin and incorpo-
rated into two important
COENZYMES (enzyme

helpers):
NICOTINAMIDE ADENINE DINUCLEOTIDE
(NAD) and its phosphate-containing analog, nicoti-
namide adenine dinucleotide phosphate (NADP).
By assisting in oxidation-reduction reactions, NAD
performs an essential role in energy production
from nutrients. NAD is required by all cells in many
aspects of metabolism, including
CARBOHYDRATE,
FATTY ACID, and AMINO ACID degradation. The re-
duced form of NADP, NADPH, participates in
reductions required for biosynthesis.
Niacinamide is the most prevalent form of this
vitamin in animal products and
MEAT, although
niacin is more prevalent in plant foods. Niacina-
mide lacks the capillary-expanding (skin-flushing)
activity of niacin and is somewhat safer than
niacin; hence it is more often used when large
amounts of the vitamin are required. Side effects of
niacinamide include nausea, headache, fatigue,
sore mouth. Large amounts can injure the liver
(jaundice). (See also
ANABOLISM; B COMPLEX; DETOX-
IFICATION; GLUTATHIONE
.)
nickel A possible TRACE MINERAL nutrient. Nickel
is now known to be an essential trace mineral
nutrient of all higher plants, including cereal grains
and legumes, which require nickel for seeds to

grow. Nickel helps plants liberate nitrogen from soil
and absorb
IRON. Nickel also seems to be a trace
mineral nutrient for some animal species, though
its function is unknown. Diets that exclude nickel
slow growth in sheep, goats, cows, and rats. Nickel
deficiency decreases red blood cell production in
these animals as well. Nickel-deficient chickens
develop abnormally. Human requirements, if any,
are unknown. A typical American diet supplies an
estimated 0.3 to 0.6 mg of nickel daily.
Like many trace minerals, minute amounts may
be essential nutrients, though high-level exposure is
hazardous. Because nickel is an industrial waste, it
nickel 459
has emerged as an environmental pollutant. The
toxicity of high doses of nickel is well documented;
for example, nickel carbonyl is a hazardous indus-
trial chemical, and exposure in the workplace is reg-
ulated. Nickel allergies are linked to jewelry; once a
person is sensitized, nickel allergies are long-lasting.
nicotinamide See
NIACINAMIDE.
nicotinamide adenine dinucleotide
(NAD,
NADH) An enzyme helper (
COENZYME) that func-
tions in oxidation/reduction reactions of cells. NAD
contains the B vitamin
NIACIN. NAD assists dehy-

drogenases, a family of enzymes that remove
hydrogen atoms from substances (oxidation). Lac-
tate dehydrogenase is a typical dehydrogenase:
This enzyme oxidizes
LACTIC ACID to PYRUVIC ACID as
an intermediate step in the formation of
GLUCOSE,
the dominant sugar used by the body. Other dehy-
drogenases oxidize fatty acids and perform oxida-
tion steps in the
KREB’S CYCLE, the central energy
yielding pathway of the cell.
Nicotinamide Adenine
Dinucleotide Phosphate (NADP, NADPH)
NADP closely resembles NAD in structure and
function. As the second coenzyme based on niacin
it contains an additional phosphate group. The
reduced form, NADPH, is used in biosynthetic
pathways, including fatty acid and cholesterol syn-
thesis. NADPH is produced by the oxidation of glu-
cose (the pentose phosphate pathway). NADPH
supports
GLUTATHIONE PEROXIDASE, an important
ANTIOXIDANT system for neutralizing oxidative dam-
age to lipids and membranes. (See also
B COMPLEX;
CARBOHYDRATE METABOLISM; FATTY ACID; OXIDATIVE
PHOSPHORYLATION
.)
nicotinic acid See NIACIN.

night blindness (nyctalopia) A condition result-
ing from a chronic deficiency of
VITAMIN A. Vitamin
A is required to form “visual purple,” the pigment
required for vision in dim light. With vitamin A
deficiency, inadequate pigment causes an abnor-
mally slow adaptation in going from vision in
strong light to dim light. Hereditary factors may
contribute to night blindness as well.
nightshade family A plant family that includes
TOMATOES, POTATOES, EGGPLANT, PEPPERS, and
tobacco. Anecdotal reports have been interpreted
by some to suggest that eating vegetables from this
family may promote joint inflammation in suscep-
tible people. However, no carefully controlled stud-
ies have been conducted, and the hyptothesis
remains unproven. Arthritic symptoms may dimin-
ish by avoiding contact with foods that cause reac-
tions. (See also
ARTHRITIS; FOOD SENSITIVITY.)
nitrate An inorganic, nitrogen-containing ion
used as a
FOOD ADDITIVE for processed MEAT and
meat products. Meat can legally contain 91 mg
added sodium or potassium nitrate per pound.
Chopped meat can contain 778 mg per pound, and
dry, cured meat can contain 991 mg per pound. Its
role in meat is not clear, though nitrate seems to
provide a reservoir for bacterial conversion to
nitrite, which acts as an antimicrobial agent. Nitrite

can be converted to a potential cancer-causing
agent called
NITROSOAMINE.
Nitrate occurs naturally in food. Green
VEGETA-
BLES are a major source of nitrates and
BEETS,
SPINACH, and LETTUCE are likely sources. The level
depends on the plant species and variety, the part
of the plant consumed, the stage of maturity, levels
of fertilizers in the soil, and the rate of plant
growth. The estimated-typical daily intake of
nitrate is 6 mg from vegetables; 9.4 mg from cured
meats; 2 mg from bread; and 1.4 mg from
FRUIT and
fruit juices. Drinking water supplies an average of
0.7 mg daily. High levels of nitrate can occur in well
water in rural areas, due to contamination from
feed lots and run-off from fertilizer-affected fields.
A limit of 10 mg of nitrate per liter has been set by
the U.S. Public Health Service.
Nitrate in well water used to prepare formula
can be a hazard for infants. Up to six months after
birth, stomach acid production in infants is low,
which permits bacteria in the intestine to convert
nitrate to nitrite. Nitrite can disable infants’ hemo-
globin and induce a condition called methenoglo-
binemia, in which nitrite-modified hemoglobin
cannot transport adequate oxygen. In older chil-
dren, nitrate is absorbed in the stomach before it

can reach intestinal bacteria that could reduce it to
nitrite. Infants drink proportionately much more
water (in formula) than adults do, and their hemo-
460 nicotinamide
globin is also more sensitive to nitrite attack. For-
mula prepared from distilled water is safer. (See
also
PROCESSED FOOD.)
nitric oxide A small, potentially toxic, compound
of oxygen and nitrogen that is also a
FREE RADICAL.
Nitric oxide is different from laughing gas, nitrous
oxide, N
2
O. Nitric oxide serves multiple functions
in the body as a freely diffusible messenger mole-
cule. It is synthesized by specific enzymes, nitric
oxide synthases, from the amino acid
ARGININE.
Nitric oxide serves as a
NEUROTRANSMITTER in the
brain and other parts of the nervous system and
perhaps plays a key role in memory. Neurotrans-
mitters are chemicals that transmit nerve impulses
between the gaps that exist between cells. When
MACROPHAGES, phagocytic cells of the immune sys-
tem, are stimulated to respond to foreign invaders
and immune activators, they produce large
amounts of nitric oxide to wage chemical warfare
against viruses and bacteria. Nitric oxide is pro-

duced by endothelial cells lining blood vessels
where it relaxes blood vessels and helps maintain
blood pressure.
Too little nitric oxide may play a role in hyper-
tension and angina. It also is involved in penile
erection and may be a factor in impotence. Nitric
oxide also interacts with blood platelets to decrease
platelet aggregation, thus lowing the risk of blood
clots. Red blood cells rapidly inactive nitric oxide
by converting it to nitrate for excretion. Excesses of
nitric oxide may be a factor in strokes and inflam-
matory bowel disease. In stroke, too much calcium
can enter cells, causing nitric oxide overproduction
to toxic levels when oxygen supply is restored.
Nitric oxide combines with
SUPEROXIDE, another
free radical produced in the body, to form perox-
ynitrite. This powerful oxidizing agent may
account for some of the cellular damage that occurs
with prolonged inflammation and could contribute
to tissue damage in colitis and other conditions.
nitrite (potassium nitrite, sodium nitrite) A com-
mon food additive to processed meat. Nitrites are
added to cure
MEATS, like LUNCHEON MEATS, liver-
wurst,
SALAMI, BACON, BOLOGNA, HAM, and HOT
DOGS
to prevent them from turning gray and to cre-
ate a meaty flavor. Cured white meat does not need

a pink color, so nitrite is not usually added to it.
Nitrite decomposes to nitric oxide, which reacts
with pigments in meat to form an appealing pink
color. Nitrites can inhibit bacterial growth, and one
argument for continuing to use sodium nitrite is
that it prevents spoilage and
BOTULISM. Dry cured
meat may contain 283 mg of nitrite per pound,
while chopped meat can contain 71 mg per pound.
Dietary vegetables supply 0.20 mg daily, while
cured meats supply several milligrams daily. Until
the late 1970s, nitrite was needlessly added to
BABY
FOOD
. Yielding to consumer pressure, baby food
manufacturers have stopped this practice. Bacterial
action on nitrate in saliva and in the intestine can
produce several milligrams of nitrite daily.
Safety
Nitrite-containing bacon, when fried, yields
NITRO-
SOAMINES, a family of nitrogen-containing, cancer-
causing chemicals. Furthermore, significant levels
of nitrosoamines appear in cooked
SAUSAGE and
cured meats. Specific nitrosoamines have caused
CANCER in all animals tested. Under conditions pre-
sent in the stomach, nitrite also can react with
AMINES found in protein-containing foods to form
nitrosoamines. Population studies have linked

nitrite intake and cancer. Although nitrites and
nitrates come from vegetables, this does not neces-
sarily lead to nitrosoamines because
VITAMIN C and
similar chemicals in the food block nitrosoamine
formation. The
FDA has approved the use of nitrites
since they themselves do not cause cancer. Fur-
thermore,
VITAMIN C (ascorbic acid) or similar
agents must be added to cured meats in order to
reduce the risk of nitrosoamines. Nitrite is now
listed on food labels. Nitrite-free meat is increas-
ingly available. (See also
CARCINOGEN; NITROGEN
CYCLE
; PRESERVATIVE.)
nitrogen One of the four major elements used to
assemble the carbon-based molecules of life. The
other three building blocks are hydrogen, carbon,
and
OXYGEN. Nitrogen is a key constituents of
AMINES, alkaline substances found in cells. In all
cells, nitrogen appears in the amino acids, which
are incorporated into protein, including enzymes;
in purines and pyrimidines, the building blocks of
DNA and RNA, the information molecules of the cell;
in
PHOSPHOLIPIDS, the structural elements of mem-
nitrogen 461

branes; in certain HORMONES; and in brain chemi-
cals (
NEUROTRANSMITTERS) synthesized by nerve
cells to carry nerve impulses. Nitrogen contributes
to the function of
HEME (the oxygen-binding pig-
ment of the oxygen-transport protein,
HEMOGLO-
BIN
); THIAMIN (vitamin B
1
);
RIBOFLAVIN (vitamin
B
2
);
NIACIN (vitamin B
3
);
VITAMIN B
6
; and
VITAMIN
B
12
. The nitrogen-containing waste product of pro-
tein metabolism is urea, excreted in the urine.
In the
NITROGEN CYCLE, atmospheric nitrogen is
reduced to ammonia by bacteria residing in the

roots of legumes like beans or alfalfa. The ammonia
is readily taken up by the plant and can be used to
fabricate all nitrogen-containing cell building
blocks, including chlorophyll. Animals eat these
plant materials primarily as amino acids in food
proteins. Cells are generally able to adapt this
nitrogen source to their own nitrogen-containing
compounds. Thus, ultimately plants are the source
of nitrogen in animal cells. Lightning can oxidize
atmospheric nitrogen to
NITRATE, which leaches
into soil as rainfall. Alternatively, nitrate, ammo-
nia, or urea fertilizers are applied during crop culti-
vation. Nitrate is rapidly absorbed by plants, while
urea breaks down to ammonia. Plant tissues can
reduce nitrate to ammonia, which is more readily
used. When plant or animal tissue decomposes,
bacteria can oxidize nitrogen to nitrate, which can
then be reabsorbed by plants to reinitiate the cycle.
Denitrifying bacteria are able to transform nitrate
back to atmospheric nitrogen (N
2
).
nitrogen balance A measure of the nutritional
state of an individual that pertains to
PROTEIN and
AMINO ACID
consumption. Nitrogen balance com-
pares the level of dietary nitrogen, as represented
by amino acids of food protein, with the amount of

their nitrogen waste products, lost in urine, feces,
and perspiration.
Proteins of every tissue are constantly being re-
placed, as they wear out due to chemical changes
and are degraded to amino acids. The released
amino acids may be reused, or they may be
degraded for energy, their nitrogen excreted pri-
marily as
UREA. If incoming protein just balances
the need for amino acids to compensate for wear
and tear, the individual is considered to be in
“nitrogen equilibrium.” Healthy adults maintaining
a steady body weight are generally in this state.
Negative Nitrogen Balance When the diet
lacks adequate amino acids for growth and mainte-
nance, demand exceeds supply. To compensate, the
body breaks down its own protein to supply amino
acids.
FASTING, ILLNESS, diabetes, fever, surgery,
STARVATION, ALCOHOLISM, severe weight loss pro-
grams, and crash
DIETING place the individual in
negative nitrogen balance.
Positive Nitrogen Balance When the body
accumulates protein and new tissue is being built,
more nitrogen is stored as protein than is lost as
waste. Positive nitrogen balance occurs during
rapid periods of growth during childhood, adoles-
cence and pregnancy.
nitrogen cycle The movement of nitrogen from

the atmosphere through organisms. Nitrogen (N
2
)
as a gas represents about 80 percent of the atmos-
phere. Though very abundant, it cannot be used by
higher organisms and must be chemically modified
to be a nutrient for plants and animals. Bacteria that
live symbiotically in the roots of legumes such as
PEAS, BEANS,and ALFALFA initiate the process. They
convert atmospheric nitrogen to the simplest nitro-
gen compound,
AMMONIA (NH
3
), via a process called
nitrogen fixation. Alternatively, lightning bolts ener-
gize nitrogen to react with oxygen in the air to cre-
ate
NITRATE
. Plants incorporate both ammonia and
nitrate into
AMINO ACIDS
, which form PROTEIN
. When
ingested by animals, plant proteins are broken down
to amino acids and incorporated into animal protein.
The most useful dietary form of nitrogen for humans
is protein: It is digested to release amino acids. Most
other nitrogen-containing cell components, like
DNA and RNA, can be constructed from amino
acids. Animals excrete nitrogenous wastes like

UREA,
the end product of protein metabolism. Soil bacteria
can convert waste nitrogen compounds back to
atmospheric nitrogen and ammonia, to be reincor-
porated into plants. Bacteria, fungi and molds decay
plant and animal tissues to help recycle key nutri-
ents. (See also
GREEN REVOLUTION; HUNGER; LEGUMES;
NITROGEN BALANCE.)
nitrosoamine A cancer-causing agent formed
from the common
FOOD ADDITIVE NITRITE. Nitrite is a
common additive in highly processed meat prod-
ucts and cured meats. Mice, rats, hamsters, pigs,
dogs, monkeys, and fish develop
CANCER when
462 nitrogen balance
exposed to several nitrosoamines, which can mod-
ify
DNA in test tube experiments. In the stomach
and intestine they can react with amines, nitrogen-
containing compounds present in many foods.
Nitrosoamines have been detected in cooked
SAUSAGE
and BACON, tobacco smoke, cured meats,
PESTICIDES
, smoked fish, powdered milk, alcoholic
beverages, and several types of industrial plants, as
well as new car interiors. The level of exposure
constituting a health hazard to humans is un-

known.
VITAMIN C and GARLIC
inhibit nitrosoamine
formation. (See also
FOOD PRESERVATION
.)
nondairy creamer
(nondairy whitener) A syn-
thetic liquid or powder replacement for milk or
cream in coffee. Consumers who choose a non-
dairy creamer may wish to choose to avoid the
calories,
CHOLESTEROL, and FAT of cream. However,
cream replacements contain 0.7 g of fat per tea-
spoon in the form of emulsified
COCONUT OIL, palm
kernel oil, or partially
HYDROGENATED VEGETABLE
OIL
. Not only does a nondairy creamer contain as
many fat calories as cream, coconut oil is the most
saturated fat available, and a high intake of satu-
rated fat promotes elevated blood fat and choles-
terol levels. Nondairy creamers do not contain
cholesterol because vegetable oils do not contain
cholesterol. On the other hand, they may contain
CORN SYRUP as a sweetener, whey and sodium
caseinate as protein emulsifiers, sodium alumi-
nosilicate as a stabilizer, as well as artificial flavor-
ing and coloring. Nondairy creamers are

nutritionally inferior to milk and are not a milk
substitute for children. (See also
IMITATION FOOD.)
nonfat dry milk See
MILK.
nonheme iron See IRON.
nonprotein nitrogen NITROGEN sources other
than protein that can be used to build proteins of
the body. Though dietary protein supplies most of
the nitrogen for protein synthesis as amino acids,
other nitrogen sources can contribute nitrogen.
AMMONIA can be reincorporated into amino acids
and hence proteins. Individuals on low-protein
diets utilize alternative sources of nitrogen more
effectively than those who are well fed.
noodles Strings or ribbons of unleavened baked
dough. The U.S.
FDA defines all pastas as either
noodles or
MACARONI. Noodles must contain one or
more of the following: milled durum
WHEAT flour,
farina (coarsely ground wheat endosperm from
less-hard wheat), or semolina (a granular product
of milled durum wheat), together with 5.5 percent
egg. (Macaroni need not contain egg.) Noodles
have been a mainstay of Asian cookery since
ancient times.
RICE flour and MUNG BEAN flour are
popular in Southeast Asia. Today, noodles are stir-

fried, pan-fried, or used in soups and sauces. Spe-
cific examples include:
• Mung bean thread noodles (transparent noodles
or jelly noodles) resemble silver threads. They
soften rapidly in water and are a staple in China,
Indonesia, Malaysia, and Japan.
• Rice noodles are thin and wiry when dry. When
soaked in water and cooked, they soften and
form the basis of many dishes. Rice noodles are
popular in Burma, Cambodia, Indonesia, and
Vietnam.
• Soba noodles are made from
BUCKWHEAT.
• Udon noodles are thick noodles prepared from
wheat flour without eggs. They can be either flat
or round.
• Bean curd noodles, also called soy noodles,
resemble typical egg noodles except they are
somewhat thicker and may be grayish in color.
(See also
SOYBEAN.)
nori See SEAWEED.
nucleic acids Substances that function as the
genetic material and the
PROTEIN synthesizing
machinery of all cells.
DNA is the genetic blueprint.
Each species possesses a unique DNA that guides all
of a cell’s structure and functions; it has been called
the cell’s “master plan.” Alterations in DNA lead to

altered inheritance.
RNA is considerably smaller than DNA and does
not function as a genetic blueprint of the body.
RNA
serves as a messenger by which information for
building proteins can be translated in the cytoplasm.
Thus, RNA directs the assembly of proteins from
amino acid raw materials. Special types of RNA form
nucleic acids 463
ribosomes, upon which proteins are constructed,
and messenger and transfer RNA to translate genetic
codewords into amino acids. Both DNA and RNA are
assembled from building blocks: a simple sugar,
DEOXYRIBOSE, phosphate, and nitrogen-containing
cyclic bases called purines and pyrimidines.
The overall composition of RNA is similar to
DNA. Each contains a phosphate, a simple sugar—
ribose in RNA and deoxyribose in DNA. RNA and
DNA contain four nitrogen-containing ring com-
pounds. Three of these are identical:
ADENINE, GUA
-
NINE
, and cytosine. In addition, RNA contains
uracil, while DNA contains thymin. (See also
FREE
RADICALS
; MUTAGEN; MUTATION
.)
“nursing bottle” syndrome Extensive dental

decay in babies due to sucking sweetened bever-
ages for a long period of time. When a baby falls
asleep with
JUICE-filled bottle or a bottle filled with
a sweet drink (even milk) in its mouth, reduced
active sucking and reduced saliva flow allow sugar
to bathe the upper teeth and lower back
TEETH.
This favors bacterial growth, cavity formation,
and, eventually, extensive dental decay. This syn-
drome can be avoided by not allowing the infant
or young child to fall asleep with a bottle of juice
or milk. (See also
BREAST-FEEDING; INFANT FOR-
MULA.)
nut A seed typically enclosed by a tough woody
shell. Nuts are products of trees;
ALMONDS, CHEST-
NUTS
, and HAZELNUTS are typical examples. The
PEANUT is an example of a nut that is usually the
pod of a
LEGUME (member of the pea family). Cer-
tain varieties of
ALMONDS and PECANS may have soft
as well as hard shells. The
COCONUT is the leading
nut crop worldwide, followed by peanuts; together
they account for 94 percent of the world nut pro-
duction. Nonetheless, nut production is small

when compared with the yield of
GRAINS and
LEGUMES, which are major food items.
Nuts have been a staple in hunter-gatherer soci-
eties since prehistoric times. Ancient civilizations
cultivated almonds,
PISTACHIO nuts, and WALNUTS in
Asia.
BRAZIL NUTS, peanuts, and cashews originated
in South America. Acorns were eaten by Native
Americans, who soaked the crushed nuts in water
to remove toxic, bitter materials (
TANNINS). Though
nuts are still harvested in America from wild trees,
often nut tree orchards permit more efficient
means of production, including mechanical har-
vesting.
Nuts contain high levels of
FAT, CARBOHYDRATE,
and
PROTEIN to nurture the sprouted seedling until
it can perform
PHOTOSYNTHESIS. Typically, one
ounce (
1
/8 cup) of most nuts contains 13 to 18 g of
fat, representing an average of 160 fat calories, and
70 percent to 90 percent of calories come from fat.
Because of their high fat content, nuts contain 140
more calories per ounce than grains and legumes.

On the other hand, the fat in unroasted nuts is
unsaturated and unprocessed, an advantage over
vegetable shortening or animal fat, which are satu-
rated fats. Brazil nuts, hazelnuts, hickory nuts,
peanuts, pecans, pistachios, and walnuts provide
4.7 to 10 g of the
ESSENTIAL FATTY ACID, LINOLEIC
ACID
, per ounce (28 g). Americans who eat nuts
frequently seem to have a lower risk of heart attack
and coronary disease.
COMPARISON OF UNSATURATED
FATTY ACID CONTENT IN TYPICAL NUTS
Calories/oz. Monounsaturated Polyunsaturated
Fat Fat
almonds (167) 68% 22%
pecans (187) 66% 26%
pistachios (162) 71% 16%
peanuts (164) 52% 33%
walnuts (182) 24% 70%
COCONUT OIL has the highest percentage of satu-
rated fatty acid of the common vegetable oils and
resists rancidity. Snack nuts (roasted nuts) are usu-
ally roasted in palm kernel oil or coconut oil,
increasing their saturated fat content. They are also
often heavily salted. A cup of roasted peanuts con-
tains 1,000 mg of sodium, one-third of the sug-
gested daily intake. Dry roasted nuts are not
cooked in oil, though they may be salted. Nut but-
ters, such as almond butter or peanut butter, can be

used as snacks. If unsweetened and if no additives
are used, nut butters are equivalent to a typical nut
snack. Although usually eaten as a snack food,
chopped nuts can be added to fruit salads, yogurt,
pancakes, pilaf, and baked goods for a pleasing
variety.
464 “nursing bottle” syndrome
Macadamia nuts contain 72 percent fat; they are
fried in deep fat and sold as high-calorie snacks or
used for confections. Pecans contain a similar high
fat level. Chestnuts differ from other nuts in that
they contain three to four times more carbohydrate
and less fat and protein than other nuts, and their
overall nutrient profile resembles that of dry corn
or rice products.
In general, shelled nuts are sold vacuum-packed
to increase their shelf life; they should be refriger-
ated or frozen to slow rancidity due to their high
unsaturated oil content. Nuts typically contain 20
percent protein by weight, similar to that found in
legumes and about twice as much as found in
GRAINS. Peanuts contain 26 percent protein, the
highest protein content among commonly avail-
able nuts. Defatted nut meal such as almond meal
and peanut flour is used as a protein-rich flour. Nut
protein contains higher amounts of most essential
AMINO ACIDS when compared to grains, but less
than legumes. Nuts contain less
LYSINE, an essential
amino acid. Mixtures of grains and cereals with

nuts provide a complementary mixture of essential
amino acids that more nearly matches dietary
requirements than either alone.
Nuts are generally good sources of the B com-
plex vitamins (like
NIACIN, RIBOFLAVIN, and THI-
AMIN), VITAMIN E, PHOSPHORUS, and MAGNESIUM.
Roasting destroys thiamin. Most nuts provide other
important trace minerals, including
CHROMIUM,
MANGANESE
, ZINC, and SELENIUM. Typically, nuts
contain up to seven times the amounts of these
minerals as found in other unprocessed foods. Nuts
also provide
CHOLINE, a nutrient required for fat
transport and nerve function. (See also
AFLATOXIN;
COMPLETE PROTEIN; PROTEIN QUALITY.)
Kris-Etherton, P. M. et al. “Nuts and Their Bioactive Con-
stituents: Effects on Serum Lipids and Other Factors
that Affect Disease Risk,” American Journal of Clinical
Nutrition 70 (1999): 504S–511S.
Nutrasweet See ASPARTAME.
nutraceutical Foods or food-derived ingredients
that have the potential of treating or preventing
chronic disease. Many ingredients in foods, particu-
larly those derived from plants, possess the ability to
benefit health. Vegetables, fruits, nuts, legumes,
spices, and teas contain substances that possibly

help prevent many of the chronic, degenerative dis-
eases that characterize aging in populations of
developed nations. In terms of anticancer effects,
the various chemicals in foods could affect the two
stages of development of cancer. They could pre-
vent damage to healthy cells’
DNA, that is, prevent
mutations. These agents may block the activation of
carcinogens, stimulate the levels of protective
enzymes that detoxify carcinogens, or trap carcino-
gens.
FLAVONOIDS are complex substances widely dis-
tributed in vegetables and fruits, often associated
with pigments (such as anthocyanins). They are
strong antioxidants, linked with cancer prevention,
increased immunity, and lowered risk of cardiovas-
cular disease. Common sources include red wine,
apples, onions, and tea.
ISOFLAVONES (such as genis-
tein) from soy possess weak estrogen activity and
apparently lower the risk of breast cancer. Organo-
sulfur compounds in
GARLIC and ONION, including
allicin, dially disulfide, and ajoene, in a addition to
saponins and flavonoids, possess strong antibacter-
ial and antiviral properties as well as anticancer
properties. Vegetables of the cabbage family (crucif-
erous vegetables) produce
SULFORAPHANE and
ISOTHIOCYANATES

, sulfur-containing chemicals, as
well as indoles that can protect against cancer by
selectively raising the levels of liver detoxifying
enzymes so that the liver can rid the body of poten-
tially mutagenic substances more readily. Many
dark green leafy vegetables and orange fruits and
vegetables contain orange pigments called
CAROTENOIDS that enhance the immune system and
function as antioxidants, preserve vision, and
inhibit tumor growth. Ellagic acid from
GRAPES
and STRAWBERRIES deactivates potential carcino-
gens. Turmeric provides curcuminoids that also
inhibit the growth of cancer cells. Regardless of the
source, food-derived preparations need to be stan-
dardized (that is, the identities and levels of key
active ingredients should be known). (See also
PHY-
TOCHEMICALS.)
nutrient An ingredient of foods that can be used
by the body for growth and maintenance of health.
Foods are mixtures of nutrients, and the relative
nutrient 465
amounts of the various nutrients in a given food
depend on conditions of growth, storage, degree of
processing, and method of cooking.
DIGESTION
releases nutrients from foods, which can then be
absorbed by the intestinal tract. Certain nutrients
must be supplied by the diet because the body can-

not manufacture them. More than 50 different
kinds of nutrients have been identified; 40 are
definitely required for human growth, develop-
ment, and health. They include
WATER, CARBOHY-
DRATE
, 10 AMINO ACIDS
, two types of ESSENTIAL
FATTY ACIDS
from
OILS and FAT, 13 VITAMINS and
15
MINERALS. These nutrients are used for energy,
to supply building blocks to replace worn out
cell constituents, and for normal cell and tissue
function.
Carbohydrates, fat, and
PROTEIN, together, repre-
sent hundreds of grams (approximately a pound) in
the adult diet. Distribution of calories among these
three
MACRONUTRIENTS varies with the culture and
the sub-population. Fat and carbohydrate are the
major fuels. Dietary protein is the primary source of
amino acids used to fashion the body’s own pro-
teins. Major minerals like
SODIUM chloride; plant
structural materials like
FIBER; and WATER are also
classified as macronutrients because large quantities

are needed. Minerals represent
ELECTROLYTES and
bony, hard structures. The body represents about 65
percent water; weight-wise, the diet must supply
more water than any other nutrient.
Vitamins and trace minerals are classified as
MICRONUTRIENTS because they are needed in only
minute amounts, ranging from micrograms
(1/1,000 gram) to milligrams (1/1,000,000 of a
gram). They can form enzyme helpers (the
B COM-
PLEX, trace minerals like ZINC and COPPER); they
may build hormones (like
VITAMIN D or IODINE); or
they may serve a protective role as an
ANTIOXIDANT
to reduce chemical damage to cells (VITAMIN C,
SELENIUM, among others).
Requirements
A majority of essential nutrients are sufficiently
well characterized to warrant recommendations for
daily allowances, whatever their source. Nutrient
allowances need to provide a reasonable margin of
safety to account for factors such as age,
STRESS,
lifestyle habits, gender, pregnancy and lactation.
The Food and Nutrition Board of the National
Research Council formulated
RECOMMENDED
DIETARY ALLOWANCES

(RDA) estimated to meet the
needs of 95 percent of healthy Americans. Nutrient
recommendations rely upon biochemical research,
clinical case histories of nutrient-deficient individ-
uals, human experimentation with suboptimal
diets, animal growth experiments and examination
of nutrient intake of healthy people. Reduced
nutrient intake as well as excessive nutrient con-
sumption can lead to
MALNUTRITION.A BALANCED
DIET
supplies all nutrients in adequate amounts to
maintain health. Reliance on foods containing high
levels of fat or calories—as sweets, fatty snack
foods, and many highly processed foods—crowds
out micronutrients like vitamins and trace miner-
als. (See also
COENZYME; COFACTOR; DIETARY GUIDE-
LINES FOR AMERICANS; FOOD PROCESSING; VITAMIN E.)
nutrient density The relative concentration of
nutrients in a food as compared to the calories
found in wholesome, unprocessed food. Fruit has a
higher nutrient density than fruit juice because
fruit contains higher proportions of nutrients like
VITAMINS
, MINERALS, PROTEIN, and FIBER, and fruit
juice has a higher nutrient density than soda pop.
This concept is especially useful in evaluating
PROCESSED FOODS
. The higher the nutrient density,

the closer the food is to the initial unprocessed
food and the more key nutrients it has. Thus,
JUNK
FOOD
and many highly processed food products
made from bleached
FLOUR, and manufactured
meal products, often have a low nutrient density.
Excessive calories contribute significantly to the
problem of overweight facing many Americans.
The
ENRICHMENT and fortification of foods and bev-
erages, the addition of vitamins and minerals,
especially to cereal grain products like
BREAKFAST
CEREALS
, flour and BREAD, together with MILK,
attempts to improve the nutrient density of these
popular foods. (See also
DIETARY GUIDELINES FOR
AMERICANS
; FAST FOOD; FOOD ADDITIVES; FOOD PRO-
CESSING; OBESITY.)
nutrition The science of FOODS, NUTRIENTS, and
their relationship to health and disease. (See also
NUTRITIONIST.)
466 nutrient density
nutritional equivalency Characteristic of a sub-
stitute or manufactured food, simulating a basic
food and containing as much of the essential nutri-

ents, as defined by the U.S. recommended daily
allowances (
USRDA), as the basic food. Thus a food
can be considered nutritionally equivalent if it is
not nutritionally inferior. There are important lim-
itations to the U.S.
FDA’s definition of nutritional
equivalency. A product can be declared nutrition-
ally equivalent though it contains excessive
amounts of any of the 20 nutrients for which
USRDA
s exist or if it contains different nutrient-to-
calorie ratios. A food that provides fewer fat calo-
ries but equal levels of essential nutrients can be
regarded as nutritionally superior. A substitute
food can be classified nutritionally equivalent to its
traditional counterpart even though it does not
contain essential nutrients such as
VITAMIN K and
many minerals—
CHROMIUM, SELENIUM, MOLYBDE-
NUM, MANGANESE, FLUORIDE—as well as MACRONU-
TRIENTS, SODIUM, POTASSIUM, and CHLORIDE.
The legal definition excludes other factors in
foods. For example, dietary
FIBER is not considered
a component of nutritional equivalency, and
uncharacterized materials in vegetables appar-
ently reduce the risk of some forms of cancer and
are excluded. Finally, the definition of nutritional

equivalency does not generally deal with
BIO-
AVAILABILITY
, that is, the degree to which nutrients
in food can be absorbed and used. Digestibility,
nutrient uptake and interrelationships among
nutrients influence nutrient availability in fabri-
cated foods. Functional laboratory tests measure
an attribute that reflects nutrient use. As an exam-
ple,
PROTEIN EFFICIENCY RATIO (PER) is a standard-
ized functional test that accesses protein
utilization of foods. (See also
FOOD LABELING; IMI-
TATION FOOD.)
nutritional supplements See VITAMIN.
nutritional status An assessment of the adequacy
of the diet in meeting individual nutrient needs.
Nutritional assessment entails a comprehensive
health evaluation: Medical history, diet analysis,
physical exam, and measurement of height and
weight can reflect nutrient status. This evaluation
may require laboratory tests to determine the tis-
sue and fluid levels of specific
VITAMINS and MINER-
ALS, or measurement of biochemical markers of
nutrient adequacy, such as serum
FERRITIN,to
assess
IRON status.

Many factors can influence a person’s nutrient
status, and sorting them out can be a challenge. An
illness can cause appetite loss or difficulty in swal-
lowing or chewing; it can interfere with
DIGESTION
or assimilation of food or alter nutrient usage or
excretion of wastes. An elderly patient may not be
able to purchase or prepare adequate food because
of physical limitations. Diminished taste with aging
may lead to the selection of salty foods. Dentures
can make chewing difficult, while diminished
stomach acid output can decrease
VITAMIN B
12
absorption as well as mineral absorption and diges-
tion in general. A lack of
EXERCISE can contribute to
problems of excessive weight. Overmedication can
lead to
DEPRESSION and disinterest in food, MALNU-
TRITION and weight loss. (See also ASSESSMENT,
NUTRITION; DIET RECORD; DIETITIAN; MALABSORPTION;
OBESITY.)
nutritional yeast See BAKER’S YEAST; BREWER’S
YEAST
; CANDIDA ALBICANS.
nutritionist A professional who specializes in
nutritional counseling. Currently, training is not
uniform from state to state. Nutritionists’ back-
grounds range from mail order credentials to

Ph.D.s from accredited universities. Most nutrition
programs require training in food science and the
biological sciences. A number of states have legisla-
tion that licenses nutritionists if they are registered
DIETITIANS or if they have an advanced degree from
a recognized college or university. A graduate of a
program in nutrition, nutrition education, or
dietetics is likely to be qualified. A number of pro-
fessional organizations offer certification programs
that assure high standards and are open to quali-
fied health care professionals, such as the Interna-
tional and American Associations of Clinical
Nutritionists and the Certification Board of Nutri-
tion Specialists.
nutrition labeling See FOOD LABELING.
nutrition labeling 467