| Phytoestrogens,
also known as phytosterols or
phytochemicals, are natural plant
compounds which have a similarity to
human estrogens. "Phyto" is
taken from Greek and is generally used as
a prefix to describe substances derived
from plants. Phytoestrogens, therefore,
are substances from plants which have
estrogen-like qualities.
The prevailing scientific
opinion on these substances is
favourable as there is substantial
research indicating that they hold great
potential for health benefits. Recent epidemiological
studies have suggested that typical Asian
diets, which have always been much higher
in these substances than Western diets,
appear to be associated with a
significantly lower risk of breast,
prostate and colon cancer as well as a
reduced incidence of heart disease and
osteoporosis. These degenerative diseases
have in fact long been associated with
modern Western diets and therefore the
studies have truly caused no surprise by
reinforcing this idea and favouring Asian
diets for good health.
The
benefits of phytoestrogens to good health
are mainly due to the effects they have
on the body's hormonal balance, acting as
both agonists and antagonists. To
understand how these substances help the
body's hormonal balance, it is useful to
recall what hormones are and how they
work. Hormones are chemical substances
produced by the body's endocrine glands
and released into the bloodstream to act
as chemical messengers, travelling
through the body with instructions to
trigger activity in their target tissues.
These target tissues each contain
receptor sites specific to a particular
hormone and the required effect is
initiated when the hormone in question
arrives and docks at those receptor
sites. For example, estrogens are
released from the ovaries and travel
through the blood to the breast area
where they dock and deliver the
instruction to initiate mammogenesis.
Phytoestrogens
are thought to act as estrogen agonists
by occupying estrogen receptor sites when
natural estrogens are unavailable. For
example, the body's natural estrogen
levels inevitably decline with the onset
of menopause and phytoestrogens may help
to offset this decline if they can fill
receptor sites instead. Once docked on
the sites they exert estrogen-like
activity and can therefore initiate the
required effect just as natural estrogen
would have done.
Phytoestrogens
are also thought to act as estrogen
antagonists by occupying estrogen
receptor sites ahead of the body's
natural estrogens and equally importantly
ahead of synthetic estrogens and also
environmental estrogens derived from
chemical products, otherwise known as bad
estrogens or xenoestrogens. In order
words, where estrogen levels are high,
phytoestrogens are able to compete with
the body's natural estrogens or the
artificial estrogens present and may fill
the receptor sites before they do. If
this happens they will in effect decrease
estrogenic activity in the body, because
the effect of the docked phytochemicals
on the target tissues will be less than
if the available estrogens had been
allowed to dock.
A
limitation on the hormone balancing
actions of these substances is that they
do not in fact have estrogenic properties
when still in the plant or even at the
time they are consumed, but acquire them
only during the digestive process through
the actions of bacteria residing in the
gastrointestinal tract. The bacteria
cause the phytochemicals to undergo
complex metabolic conversions, leading to
the formation of an estrogen-like
metabolite which can then be absorbed by
the body. What this means is that the
biologically useful forms of
phytoestrogens, the metabolites, are
dependent for their existence upon a
digestive system in good order and
complete with adequate microflora capable
of converting the basic plant compounds
into the active forms.
This
is a limitation on the effectiveness of
phytoestrogens for the simple reason that
there are a number of factors that can
adversely affect the stability of the
normal gastrointestinal flora. Poor or
inappropriate diets, stress, and
antibiotics can all significantly disrupt
the ideal healthy balance of
gastrointestinal organisms. Antibiotics
in particular can quickly destroy
friendly bacteria, as well as the
invading organisms they are actually
meant to destroy. High fat intake is
another culprit. One thing that should
have a positive effect though is fibre
intake as a high-fibre diet is known to
help the metabolism of phytochemicals.
|
