Soy food consumption may reduce risk of colon cancer
Genistein, a soy isoflavone, reduced the number of
pre-cancerous lesions in colons of lab rats exposed to a carcinogen by
5, 2013 - University of Illinois scientists say a lifelong exposure to
genistein, a bioactive component in soy foods, protects against colon
cancer by repressing a signal that leads to accelerated growth of cells,
polyps, and eventually malignant tumors.
"In our study, we report a change in the expression
of three genes that control an important signaling pathway," said Hong
Chen, a U of I professor of food science and human nutrition.
The cells in the lining of the human gut turn over
and are completely replaced weekly, she noted. "However, in 90 percent
of colon cancer patients, an important growth-promoting signal is always
on, leading to uncontrolled growth and malignancies. Our study suggests
that the aberrant
Wnt signaling during the development of colon cancer can be
regulated by soy-rich diets."
"The good news is that a diet rich in soy genistein
represses those signals through epigenetic modifications at the
regulatory regions of those genes," said Yukun Zhang, a doctoral student
in Chen's laboratory.
Genistein - Endocrine
A growing body of evidence suggests that
numerous chemicals, both natural and man-made, may interfere
with the endocrine system and produce adverse effects in
laboratory animals, wildlife, and humans. Scientists often refer
to these chemicals as endocrine disruptors.
Endocrine disruption is an important public
health concern that is being addressed by the National Institute
of Environmental Health Sciences (NIEHS).
Among the naturally
occurring endocrine disruptors are phytoestrogens. They are
naturally occurring substances in plants that have hormone-like
Examples of phytoestrogens are genistein and
daidzein, which can be found in soy-derived products.
What are endocrine disruptors?
Endocrine disruptors are naturally occurring
compounds or man-made substances that may mimic or interfere
with the function of hormones in the body. Endocrine disruptors
may turn on, shut off, or modify signals that hormones carry,
which may affect the normal functions of tissues and organs.
Chronic exposure to genistein, a soy isoflavone,
reduced the number of pre-cancerous lesions in the colons of laboratory
rats exposed to a carcinogen by 40 percent and reduced Wnt signaling to
normal levels, she said.
In their study, the scientists modeled lifetime
exposure to soy by feeding pregnant rats and their offspring a diet
containing soy protein isolate and a diet that contained genistein
compound. At seven weeks of age, offspring rats were exposed to a
carcinogen, and they continued eating either the soy protein or the
genistein diet until they were 13 weeks old.
At that time, the researchers inspected the colons
of rats in both soy groups and compared them to rats in a control group,
noting the number and severity of tiny abnormal growths in each. They
also compared Wnt signaling before and after the carcinogen to see
whether either diet had any effect on its upregulation.
In the genistein-fed animals, signaling levels were
similar to rats that had not received the carcinogen.
"Genistein decreased the expression of three genes
and repressed this signaling process that is associated with abnormal
cell growth and cancer development," Chen said.
She said this shows that colon cancer is an
epigenetic disease, meaning that dietary and environmental factors can
influence genes to be switched on or off so you have a different pattern
of gene expression, leading to a change in disease susceptibility.
It has long been known that immigrants from Asia -
where soy is traditionally a food staple - experience rising levels of
colon cancer as they adopt the eating habits of the Western nations they
now call home, she said.
"The genetic information you inherit from your
parents is not the whole story. Our dietary choices, our exposure to
environmental toxins, even our stress levels, affect the expression of
those genes," she said.
DNA methylation and histone modification of Wnt
genes by genistein during colon cancer development will appear in an
upcoming issue of Carcinogenesis.
Yukun Zhang, Qian Li, and Hong Chen, all of the
U of I, are co-authors. The study was funded by the National Institutes
of Health, U of I Research Board, and the Illinois Soybean Association.
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