From Wikipedia,
the free encyclopedia.
Nutrition is the study
of the relationship between
diet and states of
health and
disease. It is defined as the
study of food. Absence of adequate
nutrients can cause certain
diseases to take hold that can
potentially result in death.
Between the extremes of optimal
health and death from
starvation or
malnutrition, there is an
array of disease states that can
be caused or alleviated by changes
in diet. Deficiencies, excesses
and imbalances in the diet can
produce negative impacts on
health, which may result in
diseases such as
scurvy,
obesity or
osteoporosis. Also, excess
ingestion of elements that have no
apparent role in health (e.g.
lead,
mercury,
PCBs,
dioxins) may have
toxic and potentially lethal
effects depending on dose.
The science of nutrition
attempts to understand how and why
specific aspects of diet have
specific influences on health.
Overview
The
human body comprises
chemical compounds such as
water,
amino acids (proteins),
fatty acids (lipids),
nucleic acids (DNA/RNA),
and
carbohydrates (e.g.
sugars). These compounds in
turn consist of
elements such as
carbon,
hydrogen,
oxygen,
nitrogen, and
phosphorus, and may or may not
contain
minerals such as
calcium,
iron, and
zinc. Minerals also
ubiquitously occur in the form of
salts and
electrolytes. All of these
chemical compounds and elements
occur in various forms and
combinations (e.g.
hormones/vitamins,
phospholipids,
hydroxyapatite), both in the
human body and in organisms
(e.g. plants, animals) that humans
eat.
The human body must necessarily
comprise those elements that
humans eat and absorb into the
bloodstream. The
digestive system, except in
the unborn fetus, is the first
step in helping to make the
different chemical compounds and
elements in food available for the
trillions of
cells of the body. In the
digestive process of an average
adult, about seven (7) litres of
liquid, known as digestive juices,
exit the internal body and enter
the
lumen of the digestive tract.
The digestive juices help break
chemical bonds between
ingested compounds as well as
modulate the
conformation and/or energetic
state of the compounds/elements.
Yet many compounds/elements are
absorbed into the bloodstream
unchanged, though the digestive
process helps to release them from
the matrix of the foods where they
occur. Any unabsorbed matter is
eliminated in the
feces. Only a minimal amount
of digestive juice is eliminated
this way; the intestines reabsorb
most of it otherwise the body
would rapidly dehydrate (hence the
devastating effects of persistent
diarrhea).
Study in this field must take
into careful account the state of
the body before
ingestion and after
digestion as well as the
chemical content of both the
food and the waste. The specific
types of compounds and elements
that are absorbed by the body can
be determined by comparing the
waste to the food. The effect that
the absorbed matter has on the
body can be determined by finding
the difference between the
pre-ingestion state and the
post-digestion state. The effect
may only be discernible after an
extended period of time in which
all food and ingestion must be
exactly regulated and all waste
must be analyzed. The number of
variables (e.g. 'confounding
factors') involved in this type of
experimentation is very high.
This makes
scientifically valid
nutritional study very
time-consuming and expensive,
which accounts for why a proper
science of human nutrition is
rather new.
In general, eating a variety of
fresh, whole (unprocessed) foods
has proven hormonally and
metabolically favourable compared
to eating a monotonous diet based
on processed foods. In particular,
fresh, whole foods provide higher
amounts and a more favourable
balance of essential and vital
nutrients per unit of energy,
resulting in better management of
cell growth, maintenance, and
mitosis (cell division) as
well as of appetite and energy
balance. A generally more regular
eating pattern (e.g. eating
medium-sized meals every 3 to 4
hours) has also proven more
hormonally and metabolically
favourable than infrequent,
haphazard food intake.
Nutrition and health
Ill health can be brought about
by an imbalance of nutrients,
producing either an excess or
deficiency which in turn affects
body functioning in a cumulative
manner. Moreover, because most
nutrients are, in some way or the
other, involved in cell-to-cell
signalling (e.g. as building block
or part of a hormone or
signalling 'cascades'),
deficiency or excess of various
nutrients affects hormonal
function also indirectly.
Thus, because they largely
regulate the expression of genes,
hormones represent a link between
nutrition and how our genes are
expressed, i.e. our
phenotype. The strength and
nature of this link are
continually under investigation,
but observations especially in
recent years have demonstrated a
pivotal role for nutrition in
hormonal activity and function and
therefore in health.
Mineral and/or
vitamin (tocotrienol
and
tocopherol) deficiency or
excess may yield symptoms of
diminishing health such as
goitre,
scurvy,
osteoporosis, weak
immune system, disorders of
cell
metabolism, certain forms of
cancer, symptoms of premature
aging, and poor
psychological health
(including
eating disorders). The list
goes on and on; for reference, see
Modern Nutrition in Health and
Disease by Shils et al.
As of
2005, twelve vitamins and
about the same number of minerals
are recognized as 'essential
nutrients', meaning that they must
be consumed and absorbed - or, in
the case of
vitamin D, alternatively
synthesized via
UVB radiation - to prevent
deficiency symptoms and death.
Certain vitamin-like substances
found in foods, such as
carnitine, have also been
found essential to survival and
health, but these are not strictly
'essential' to eat because the
body can produce them from other
compounds. Moreover, thousands of
different
phytochemicals have recently
been discovered in food
(particularly in fresh
vegetables), which have many
discovered and yet to be
discovered properties including
antioxidant activity (see
below). Other essential nutrients
include
essential amino acids,
choline and the
essential fatty acids.
In addition to sufficient
intake, an appropriate balance of
essential fatty acids -
omega-3 and
omega-6 fatty acids - has been
discovered to be crucial for
maintaining health. Both of these
unique "omega" long-chain
polyunsaturated fatty acids
are
substrates for a class of
eicosanoids known as
prostaglandins. The omega-3
eicosapentaenoic acid (EPA)
(which can be made in the body
from the omega-3 essential fatty
acid alpha-linolenic
acid (LNA), or taken in
through marine food sources),
serves as building block for
series 3 prostaglandins (e.g.
weakly-inflammation
PGE3). The omega-6
dihomo-gamma-linolenic acid (DGLA)
serves as building block for
series 1 prostaglandins (e.g.
anti-inflammatory PGE1), whereas
arachidonic acid (AA) serves as
building block for series 2
prostaglandins (e.g.
pro-inflammatory PGE1). Both DGLA
and AA are made from the omega-6
linoleic acid (LA) in the
body, or can be taken in directly
through food. An appropriately
balanced intake of omega-3 and
omega-6 partly determines the
relative production of different
prostaglandins, which partly
explains the importance of
omega-3/omega-6 balance for
cardiovascular health. In
industrialised societies, people
generally consume large amounts of
processed vegetable oils that have
reduced amounts of essential fatty
acids along with an excessive
amount of omega-6 relative to
omega-3.
The rate of conversions of
omega-6 DGLA to AA largely
determines the production of the
respective prostaglandins PGE1 and
PGE2. Omega-3 EPA prevents AA from
being released from membranes,
thereby skewing prostaglandin
balance away from pro-inflammatory
PGE2 made from AA toward
anti-inflammatory PGE1 made from
DGLA. Moreover, the conversion (desaturation)
of DGLA to AA is controlled by the
enzyme delta-5-desaturase, which
in turn is controlled by hormones
such as
insulin (up-regulation) and
glucagon (down-regulation).
Because different types and
amounts of food eaten/absorbed
affect insulin, glucagon and other
hormones to varying degrees, not
only the amount of omega-3 versus
omega-6 eaten but also the general
composition of the diet therefore
determine health implications in
relation to essential fatty acids,
inflammation (e.g. immune
function) and
mitosis (i.e. cell division).
Several lines of evidence
indicate lifestyle-induced
hyperinsulinemia and reduced
insulin function (i.e.
insulin resistance) as a
decisive factor in many disease
states. For example,
hyperinsulinemia and insulin
resistance are strongly linked to
chronic inflammation, which in
turn is strongly linked to a
variety of adverse developments
such as arterial microinjuries and
clot formation (i.e. heart
disease) and exaggerated cell
division (i.e. cancer).
Hyperinsulinemia and insulin
resistance (the so-called
metabolic syndrome) are
characterized by a combination of
abdominal
obesity, elevated
blood sugar, elevated
blood pressure, elevated blood
triglycerides, and reduced HDL
cholesterol. The negative
impact of hyperinsulinemia on
prostaglandin PGE1/PGE2 balance
may be significant.
The state of
obesity clearly contributes to
insulin resistance, which in turn
can cause
type 2 diabetes. Virtually all
obese and most type 2 diabetic
individuals have marked insulin
resistance. Although the
association between overfatness
and insulin resistance is clear,
the exact (likely multifarious)
causes of insulin resistance
remain less clear. Importantly, it
has been demonstrated that
appropriate exercise, more regular
food intake and reducing glycemic
load (see below) all can reverse
insulin resistance in overfat
individuals (and thereby lower
blood sugar levels in those who
have type 2 diabetes).
Overfatness can unfavourably
alter hormonal and metabolic
status via resistance to the
hormone
leptin, and a vicious cycle
may occur in which insulin/leptin
resistance and overfatness
aggravate one another. The vicious
cycle is putatively fuelled by
continuously high insulin/leptin
stimulation and fat storage, as a
result of high intake of strongly
insulin/leptin stimulating foods
and energy. Both insulin and
leptin normally function as
satiety signals to the
hypothalamus in the brain;
however, insulin/leptin resistance
may reduce this signal and
therefore allow continued
overfeeding despite large bodyfat
stores. In addition, reduced
leptin signalling to the brain may
reduce leptin's normal effect to
maintain an appropriately high
metabolic rate.
There is debate about how and
to what extent different dietary
factors - e.g. intake of processed
carbohydrates, total protein, fat,
and carbohydrate intake, intake of
saturated and trans fatty acids,
and low intake of
vitamins/minerals - contribute to
the development of insulin- and
leptin resistance. In any case,
analogous to the way modern
man-made pollution may potentially
overwhelm the environment's
ability to maintain 'homeostasis',
the recent explosive introduction
of high Glycemic Index- and
processed foods into the human
diet may potentially overwhelm the
body's ability to maintain
homeostasis and health (as
evidenced by the metabolic
syndrome epidemic).
Antioxidants are another
recent discovery. As cellular
metabolism/energy production
requires oxygen, potentially
damaging (e.g.
mutation causing) compounds
known as radical oxygen species or
free radicals may form. For
normal cellular maintenance,
growth, and division, these free
radicals must be sufficiently
neutralized by antioxidant
compounds, such as certain
vitamins (vitamin
C,
vitamin E,
vitamin K and the
aforementioned phytochemicals as
well as other compounds, some of
which the body itself produces.
Different antioxidants are now
known to function in a cooperative
network, e.g. vitamin C can
reactivate free radical-containing
glutathione or vitamin E by
accepting the free radical itself,
and so on.
It is now also known that the
human digestion system contains a
population of a range of bacteria
which are essential to digestion,
and which are also affected by the
food we eat. The role and
significance of the intestinal
bacterial flora is under
investigation.
Nutrition and sports
(Stub, please expand.)
Nutrition is very important for
improving sports performance. The
most common means to improve
performance through diet is the
practice of eating large
quantities of protein, usually red
meat, when attempting to build
muscle mass; its efficacy is
doubtful, as daily protein intake
even on a normal diet usually
outweighs the amount of muscle
protein which can be synthesized
in a day, and protein is a much
less efficient source of the
energy needed to build new muscle
tissue than are fats and
carbohydrates.
Nutrition and longevity
Lifespan is somehow related to
the amount of
food energy consumed: this was
first systematically investigated
in the seminal study by Weidruch,
et al. (1986). A pursuit of this
principle of
caloric restriction followed,
involving research into
longevity of those who reduced
their food energy intake while
attempting to optimize their
micronutrient intake. Perhaps not
surprisingly, some people found
that cutting down on food reduced
their quality of life so
considerably as to negate any
possible advantages of lengthening
their lives. However, a small set
of individuals persists in the
lifestyle, going so far as to
monitor blood lipid levels and
glucose response every few months.
See
Calorie Restriction Society.
Underlying this research was
the hypothesis that oxidative
damage was the agent which
accelerated aging, and that aging
was retarded when the amount of
carbohydrates (and thereby insulin
release) was reduced through
dietary restriction.
However, recent research has
produced increased longevity in
animals (and shows promise for
increased human longevity) through
the use of insulin uptake
retardation. This was done through
altering an animal’s metabolism to
allow it to consume similar
food-energy levels to other
animals, but without building up
fatty tissue. (Bluher et al, 2003)
This has set researchers off on
a line of study which presumes
that it is not low food energy
consumption which increases
longevity. Instead, longevity may
depend on an efficient fat
processing metabolism, and the
consequent long term efficient
functioning of our organs free
from the encumbrance of
accumulating fatty deposits. (Das
et al, 2004) Thus, longevity may
be related to maintained insulin
sensitivity. However, several
other factors including low body
temperature seem to promote
longevity also and it is unclear
to what extent each of them
contribute.
Antioxidants have recently
come to the forefront of longevity
studies which have included the
FDA and
Brunswick labs. In 2005 the
FDA issued a statement
recommending that Americans should
be consuming 7,000
ORAC units daily or 12 full
servings of fruit in order to curb
the cancer epidemic. The dietary
supplement industry has responded
by shifting focus away from
hormone replacements to “super”
antioxidants such as
Proleva which contain whole
fruit extracts and ORAC scores
near 5,000 units mark or two
thirds of the new level set by the
FDA.
Nutrition, industry and food
processing
Since the
Industrial Revolution some two
hundred years ago, the food
processing industry has invented
many
technologies that both help
keep foods fresh longer and alter
the fresh state of food as they
appear in nature. Cooling is the
primary technology that can help
maintain freshness, whereas many
more technologies have been
invented to allow foods to last
longer without becoming spoiled.
These latter technologies include
pasteurisation,
autoclavation,
drying,
salting, and separation of
various components, and all appear
to alter the original nutritional
contents of food. Pasteurisation
and autoclavation (heating
techniques) have no doubt improved
the safety of many common foods,
preventing epidemics of bacterial
infection. But some of the (new)
food processing technologies
undoubtedly have downfalls as
well.
Modern separation techniques
such as
milling,
centrifugation, and
pressing have enabled
upconcentration of particular
components of food, yielding
flour, oils, juices and so on, and
even separate fatty acids, amino
acids, vitamins, and minerals.
Inevitably, such large scale
upconcentration changes the
nutritional content of food,
saving certain nutrients while
removing others. Heating
techniques may also reduce food's
content of many heat-labile
nutrients such as certain vitamins
and phytochemicals, and possibly
other yet to be discovered
substances. Because of reduced
nutritional value, processed foods
are often 'enriched' or
'fortified' with some of the most
critical nutrients (usually
certain vitamins) that were lost
during processing. Nonetheless,
processed foods tend to have an
inferior nutritional profile than
do whole, fresh foods, regarding
content of both sugar and high GI
starches,
potassium/sodium,
vitamins, fibre, and of intact,
unoxidized (essential) fatty
acids. In addition, processed
foods often contain potentially
harmful substances such as
oxidized fats and trans fatty
acids.
A dramatic example of the
effect of food processing on a
population's health is the history
of epidemics of
beri-beri in people subsisting
on polished rice. Removing the
outer layer of rice by polishing
it removes with it the essential
vitamin
thiamin, causing beri-beri.
Another example is the development
of
scurvy among infants in the
late 1800's in the United States.
It turned out that the vast
majority of sufferers were being
fed milk that had been
heat-treated (as suggested by
Pasteur) to control bacterial
disease. Pasteurisation was
effective against bacteria, but it
destroyed the vitamin C.
As mentioned, lifestyle- and
obesity-related diseases are
becoming increasingly prevalent
all around the world. There is
little doubt that the increasingly
widespread application of some
modern food processing
technologies has contributed to
this development. The food
processing industry is a major
part of modern economy, and as
such it is influential in
political decisions (e.g.
nutritional recommendations,
agricultural subsidising). In any
known profit-driven economy,
health considerations are hardly a
priority; effective production of
cheap foods with a long shelf-life
is more the trend. In general,
whole, fresh foods have a
relatively short shelf-life and
are less profitable to produce and
sell than are more processed
foods. Thus the consumer is left
with the choice between more
expensive but nutritionally
superior whole, fresh foods, and
cheap, usually nutritionally
inferior processed foods. Because
processed foods are often cheaper,
more convenient (in both
purchasing, storage, and
preparation), and more available,
the consumption of nutritionally
inferior foods has been increasing
throughout the world along with
many nutrition-related health
complications.
Policy advice and guidance on
nutrition
Most Governments provide
guidance on good nutrition, and
some also impose
mandatory labelling
requirements upon processed food
manufacturers to assist consumers
in complying with such guidance.
Current dietary guidelines in the
United States are presented in the
concept of a
food pyramid. There is no
apparent consisteny in
science-based nutritional
recommendations between countries,
indicating the role of
politics as well as
cultural bias in research
emphasis and interpretation.
Current issues and challenges
Challenging issues in modern
nutrition include:
'Artificial' interventions
in food production and supply:
Sociological issues:
- How do we minimise the
current disparity in food
availability between first and
third world populations (see
famine and
poverty)?
- How can public advice
agencies, policy making and food
supply companies be coordinated
to promote healthy eating and
make wholesome foods more
convenient and available?
- Do we need
nutritional supplements in
the form of pills, powders,
liquids, etc.?
- How can the developed world
promote good worldwide nutrition
through minimising import
tariffs and export subsidies on
food transfers?
Research Issues:
- How do different nutrients
affect appetite and metabolism,
and what are the molecular
mechanisms?
- What yet to be discovered
important roles do vitamins,
minerals, and other nutrients
play in metabolism and health?
- Are the current
recommendations for intake of
vitamins and minerals generally
too low?
- How and why do different
cell types respond differently
to chronically elevated
circulating levels of insulin,
leptin, and other hormones?
- What does it take for
insulin resistance to develop?
- What other molecular
mechanisms may explain the link
between nutrition and
lifestyle-related diseases?
- What role does the
intestinal bacterial flora play
in digestion and health?
- How essential to proper
digestion are the
enzymes contained in food
itself, which are usually
destroyed in cooking (see
Living foods diet)?
- What more can we discover
through what has been called the
phytochemical revolution?
See also
For detailed information, see
related entries in the following
categories:
Food:
Health:
Research:
References
- Shils et al. (2005)
Modern Nutrition in Health and
Disease, Lippincott Williams
and Wilkins. ISBN: 0781741335.
- Bluher, Khan BP, Kahn CR,
Extended longevity in mice
lacking the insulin receptor in
adipose tissue.
Science 299(5606):
572-4, Jan 24, 2003.
-
The Times newspaper,
January 31 2004 Could
vitamins help delay the onset of
Alzheimer’s? by Jerome Burne.
- The Times newspaper
February 28, 2004 Autism: I
can see clearly now . . . by
Simon Crompton
- The Times newspaper
March 10, 2004 Work up an
Amish appetite by Anne-Celine
Jaeger
- Das M, Gabriely I, Barzilai
N.Caloric restriction, body
fat and aging in experimental
models. Obes Rev. 2004
Feb;5(1):13-9.
- William Eaton et al
Coeliac disease and
schizophrenia British
Medical Journal, February 21,
2004.
- Janssen I, Katzmarzyk PT,
Ross R. Waist circumference
and not body mass index explains
obesity-related health risk.
Am J Clin Nutr. 2004
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dietary phytoestrogen intake and
bone mineral density in
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- Merritt JC "Metabolic
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serum lipids."J Natl Med Assoc.
2004 Aug;96(8):1032-41.
- Sobczak S, et al Lower
high-density lipoprotein
cholesterol and increased
omega-6 polyunsaturated fatty
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of bipolar patients Psychol
Med. 2004 Jan;34(1):103-12.
- Walter C. Willett and Meir
J. Stampfer,Rebuilding the
Food Pyramid, Scientific
American January 2003.
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retardation of aging in mice by
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