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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. In addition, as mentioned, the type and
amount of foods Pharmacy Health Topic we eat affect the body's hormonal environment directly,
and a persistent intake of (a certain amount of) certain foods may
induce hormonal imbalance and thereby disease. 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), 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 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 unsaturated fatty acids are substrates
for a class of eicosanoids known as prostaglandins). Alpha-linolenic
acid (LNA) serves as the building block for the less-inflammatory
PGE3 series of prostaglandins, whereas linoleic acid (LA) (and specifically
its product, arachidonic acid, AA) serves as the building block
for either the PGE1 (anti-inflammatory) or the PGE2 (pro-inflammatory)
series. (The omega-6 fatty acid LA is the building block for the
omega-6 fatty acid AA, but AA can also be obtained directly in the
diet). The Pharmacy Health Topic conversions of AA into the respective prostaglandins
(PGE1/PGE2) have importantly been discovered to be under hormonal
control, as certain hormones such as insulin and glucagon regulate
the function of the enzymes responsible for the conversions. 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 is now known to 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
insulin malfunction, referred to as insulin resistance, as a decisive
factor in many disease states. Researchers have for long assumed
that overfatness/obesity causes insulin resistance, which in turn
causes type 2 diabetes (virtually all obese and diabetic individuals
have marked insulin resistance). More recent evidence has however
demonstrated that insulin resistance may well be the cause of overfatness/obesity
as well as type 2 diabetes and possibly other lifestyle-related
diseases. For example, it has been demonstrated that appropriate
exercise, more regular food intake and reducing glycemic load all
can reverse insulin resistance in overfat individuals, which means
that lifestyle rather than the fact of being fat promotes insulin
resistance.
Nonetheless, overfatness can unfavourably alter hormonal
and metabolic status seemingly especially via the hormone leptin,
and a vicious cycle may occur in which insulin/leptin resistance
and overfatness aggravate one another. There is debate to what extent
different dietary factors, such as intake of processed carbohydrates,
total protein-, fat-, and carbohydrate intake, intake of trans fatty
acids, and low intake of micronutrients, contribute to develop insulin-
and leptin resistance. Most importantly, insulin- and leptin resistance
are both 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
over-expressed cell division (i.e. cancer).
A persistent high intake of processed carbohydrate-dense
foods (high glycemic load) resulting in repeatedly high release
of insulin and leptin seems to readily make cells less responsive
to both of these crucial hormones (perhaps especially in combination
with high intake of saturated fat/trans fatty acids and sedentary
living). This type of negative feedback is ubiquitous in any biological
system, all of which depend on appropriate hormonal regulation for
survival and proper function. However, certain cell types appear
to more readily become resistant to the effects of certain hormones
(e.g. insulin, leptin) than others; certain fat cells (e.g. abdominal
subcutaneous fat) may respond well to the fat-storing signal of
insulin while other cells fail to properly receive/transduce the
signal meant to induce important cellular and systemic effects.
Why certain cells develop resistance to certain signalling molecules
remains unclear, but it seems plausible that hormone resistance
serves to protect cells from excess circulating amounts of the given
hormone. 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, for example,
the obesity 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. Pharmacy Health Topic 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.
It is now commonly accepted amongst the medical profession
that a diet high in fresh fruit and vegetables but low in animal
fat helps to prevent heart disease and cancer.
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