| Epidemiology population
studies shows differences in death rates from cancer in
different parts of the globe. For example, death rates
for breast cancer are more than 2-1/2 times higher in
American women than in Japanese women. And, American men
have death rates from prostate cancer that are more than
triple those of Japanese men.
In their search for an explanation of these differences,
scientists have investigated a number of factors, including
diet. Although eating habits in the East and West differ
in a number of ways, a considerable amount of research
is currently investigating the potentially protective
effects of soy. Soyfoods are a major source of protein
in many traditional Asian cuisines while being almost
completely absent in most Western diets.
How Might Soy Protein Help Reduce
the Risk of Cancer?
Researchers are working to discover if substances in
soy protein may help explain the differences in death
rates from certain cancers. They are investigating a
number of potential mechanisms by which specific components
of soy protein may relate to cancer risk. The components
of soy receiving the most interest include: isoflavones-including
genistein, daidzein, and glycitein, as well as their
conjugates; phytic acid; protease inhibitors, especially
the Bowman Birk Inhibitor; saponins; amino acids; and
other compounds.
Anticancer Mechanisms Under Study
Researchers are looking at the effects of different
substances in soy protein on the development and spread
of cancer. Some mechanisms of action prevent initial
damage to the cell, and others involve interfering with
steps in the promotion of cancer. Many of these proposed
mechanisms being researched involve the bioactives in
soy protein.
Antioxidant effect. Oxidation is a chemical
reaction that can damage the DNA in cells and initiate
cancer. Antioxidants are substances that reduce or prevent
oxidation. The body constantly makes antioxidants, and
others are found in foods, including soybeans.
Both laboratory and animal studies have shown that
genistein acts as an antioxidant. These
antioxidant properties may be at least partly responsible
for the antitumorigenic effects observed in animal studies.
Phytic acid (or phytate), which is present in soy,
can bind with certain minerals, including iron, inhibiting
their absorption in the intestinal tract. This is important
because iron can promote oxidation and is known to be
associated with both the initiation and promotional
phases of cancer. A number of studies in
animals have suggested that the phytic acid in soy may
help reduce the risk of colon cancer.
Antiangiogenic effect. Whenever the body grows new
tissues, it must also provide a blood supply to "feed"
them. This process of developing tiny new blood vessels--capillaries--
is called angiogenesis. Angiogenesis is much more common
in growing infants and children. In adults, angiogenesis
normally occurs only during menstruation or during the
healing of a wound.
As abnormal areas of new growth, tumors also require
a blood supply if they are to increase in size and metastasize.
Tumors that don't have a sufficient blood supply are
likely to remain tiny, causing little or no harm.
Antiangiogenic agents are substances that can prevent
the development of new blood vessels. They act somewhat
like a tourniquet, cutting the tumor off from the blood
it needs to grow. Some research shows that genistein
can inhibit angiogenesis in the laboratory
and reduce angiogenesis in experimentally induced urinary
bladder tumors and prostate tumors
in animals.
Effect on the stress response. Under certain
stressful conditions, cells can cause production of
stress proteins that protect them against normal programmed
cell death-apoptosis. One of these stressful conditions
is the onset of cancer. Therefore, cancer cells may
live-and continue to multiply-well beyond their normal
life span. Research has shown that genistein can inhibit
the stress response in the laboratory.
Effects on the immune system. How well your
immune system functions is an important factor in the
development of cancer. Research suggests that daidzein,
the second most plentiful isoflavone in soy, enhanced
several functions of the immune system in animals.
Effect on tyrosine kinases. Tyrosine kinases
are enzymes essential to the development of certain
cancers. Therefore, tyrosine kinase inhibitors have
been studied as possible anticancer agents. Although
genistein is known to be a tyrosine kinase inhibitor,
some researchers found that genistein inhibited the
growth of breast cancer cells in the laboratory without
greatly reducing tyrosine kinase activity.
Antipromotional effects. Different components
in soy have been studied for their relationship to the
promotional phase of cancer. The Bowman-Birk inhibitor
found in soy, for example, has been found to be a very
effective anticancer agent.
Considerable research has focused on the potential
antipromotional effects of soy isoflavones. In one study,
low levels of genistein decreased the number of tumors
in mice by about half and significantly prolonged tumor
latency. Studies have also shown that genistein
reduced the multiplication of breast cancer cells in
the laboratory. Interestingly enough,
genistein appeared to be effective in inhibiting growth
in both hormone-dependent and non-hormone-dependent
breast cancer cells.
Cancers Under Study
Researchers have focused on the potential role of soy
and/or soy protein with its biologically active components
on cancers at a number of sites. Of particular interest
are breast, prostate, and colon cancer.
References
View cancer
references list.
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