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- Researchers say they've discovered why diets high in
soy can lower your cholesterol in some instances. It's well known that
diets high in soy can have dramatic effects on your cholesterol level.
Now, scientists in North Carolina have found, apparently for the first
time, what it is in soy that inhibits cholesterol.
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- In their study published in the
current issue of the
Archives of Internal Medicine, researchers claim
that the cholesterol-lowering
effect of soy depends largely on the
amount of isoflavones that are present,
which are plant estrogens. The
higher the amount of isoflavones in the
soy, the larger the effect,
they say.
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- In the same way, the scientists say isoflavones that
have been
extracted from soy do not lower cholesterol, nor does a relatively
low
dose of this estrogen.
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- In the study, 156 people with moderately high
cholesterol
levels were picked at random to eat one of several diets
over a period
of nine weeks: one that contained levels of casein, a
protein isolated
from milk; and others that contained varying levels of
isoflavones.
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- "What we saw was that there was no effect of the
casein,
and that the soy reduced levels of total and low-density (so called
"bad") cholesterol," said John Crouse, MD, a professor of
Internal Medicine and Public Health Sciences at Wake Forest University
who led the research.
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- In the group of people who ate the highest level of soy
protein, the results were dramatic. In just over two months, levels of
"bad" cholesterol dropped by 10 percent among those who had the
highest cholesterol levels in that group. That "bad"
cholesterol,
also known as low-density lipoprotein (LDL), is the
substance that doctors
believe increases the risk of heart
disease.
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- Even when the researchers combined all those with varying
LDL
cholesterol levels, high amounts of soy still reduced that cholesterol
by as much as 6 percent.
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- By contrast, those people who ate diets that contained
the lowest levels of soy, or diets in which isoflavones were extracted,
showed little decline in cholesterol levels.
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- There was also evidence of what
health experts call a
"dose response relationship"; that is,
an increase in the amount
of isoflavones caused a direct decrease in
cholesterol levels. Higher levels
of the estrogen also dropped blood
pressure levels among women who participated.
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- However, other research has
found that the isoflavones
alone do not provide the same effect. It
only works, Dr. Crouse says, if
they are consumed in soy
protein.
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- Initially, all participants were placed on casein milk
shakes,
then certain individuals were selected at random to change their
diets
to soy protein, explained Dr. Crouse. The researchers determined
their
conclusions by measuring blood lipid levels before the soy diets
were
introduced, as well as afterwards.
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- Lipids are organic substances
made up of fats or fatty
acids. High lipid levels in the bloodstream
can potentially be a precursor
to atherosclerosis.
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- Dr. Crouse and his colleagues
also noted that people
living in Asia consume 30 to 50 times more soy
than their counterparts
in the Western Hemisphere. People in those
countries, as a result, have
a much lower prevalence disease.
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- In fact, nearly a
thousand times as many isoflavones
are found in the urine of those
living in Asia, compared to American populations,
based on
statistics.
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- "This is a subject of active investigation at the
present
time, but it seems that soy may have a number of effects that are
beneficial in chronic diseases, including ... breast cancer, possibly has
an effect on menopausal symptoms in women ... and also on cardiovascular
disease and stroke," Crouse tells TheHealthNetwork.com.
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- One reason is that
the chemical structure of isoflavones
is similar to estrogen, he said,
adding that a range of animal studies
at Wake Forest have confirmed
that isoflavones provided this disease protection.
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- For people with cholesterol
problems, there is one common
food that contains this soy
ingredient.
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- "Probably tofu is the foodstuff that has the highest
concentration of isoflavones," Crouse said.
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- The highest levels of soy
protein used in this study
were equal to consuming about a half to
two-thirds of a tofu cake each
day.
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- "If you stop the diet, the
cholesterol would drift
back up again," said Crouse.
"Elevated cholesterol is a chronic
problem that needs chronic
attention."
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