Soy Protein

Periodically, I'll be sharing some research newsletters from Dr. Stephen Chaney. Dr. Chaney is Professor of Biochemistry & Biophysics and Professor of Biochemistry, University of North Carolina at Chapel Hill.

This particular newsletter discusses the effect of soy protein in women with breast cancer. Here's Dr. Chaney:

"You've probably heard the warnings: "Soy may increase
the risk of breast cancer!" "Women with breast cancer
shouldn't use soy!".

The first warning was never true. Numerous clinical
studies have shown that consumption of soy protein is
associated with a lower risk of developing breast
cancer.

Furthermore, the science behind the second warning has
never been very strong. The concerns that soy might
stimulate the growth of breast cancer cells was based
primarily on cell culture experiments and one
experiment in mice - even though a second experiment in
mice came to the exact opposite conclusion.

However, the possibility that soy isoflavones could
stimulate the growth of estrogen- responsive breast
cancer was biochemically plausible because soy
isoflavones bind to the estrogen receptor and have a
very weak stimulatory effect (much weaker than estrogen
itself).

Even that evidence was not definitive because soy
isoflavones also turn on several tumor
suppressor pathways in breast cells and help strengthen
the immune system - so they could just as easily
inhibit the growth of breast cancer cells.

However, because the concerns were plausible and had
not been definitively disproved, most experts,
including me, have recommended that women with
estrogen- responsive breast cancer might want to avoid
soy protein.

Well a definitive study has finally been performed and
it turns out for women with breast cancer, consumption
of soy foods actually decreases their risk of breast cancer
recurrence and dying from breast cancer.

The study was reported in the December 2009 issue of
the Journal of the American Medical Association by
researchers at Vanderbilt University and Shanghai
Institute of Preventive Medicine.

It was a large, well designed, study that enrolled 5042
Chinese women aged 20 to 75 years old who had been
diagnosed with breast cancer and followed them for an
average period of 3.9 years.

The women were divided into four groups based on the
soy content of their diet (ranging from 5 grams/day to
15 grams/day).

The results were clear cut. Breast cancer survivors
with the highest soy intake had 25% less chance of
breast cancer recurrence and 25% less chance of dying
from breast cancer than the women with the lowest soy
intake.

The effect was equally strong for women with estrogen
receptor-positive and estrogen receptor negative
cancers, for early stage and late stage breast cancer
and for pre- and post-menopausal women.

In short this was a very robust study.

The study also showed that soy protein intake did not
interfere with tamoxifen. The reduction in the risk of
breast cancer recurrence & death was just as great
whether the breast cancer survivors were taking
tamoxifen or not.

In fact, tamoxifen was protective only for women with
low soy intake. It conferred no extra protection for
the women at the highest level of soy intake.

What does this mean for you if you are a breast cancer
survivor?

I personally feel that this study is clear cut enough
that breast cancer survivors no longer need to fear soy
protein as part of a healthy diet.

However. it is important to recognize that this is a
single study. It is a very good study, but it is just
one study.

As a scientist and a cancer researcher I would like to
see this study confirmed by other studies before
recommending that all women who have had breast cancer
should add soy protein to their diets. It may turn out
that some women will benefit much more from using soy
protein than others.

Similarly, this study suggests that soy protein does
not interfere with tamoxifen.

But the use of tamoxifen after breast cancer remission
is a medical treatment - and all medical treatments
should be discussed with your doctor.

Finally, I would like to point out that a number of
previous studies have suggested that isolated
isoflavones may not have the same benefits as soy
protein foods containing the isoflavones - so I don't
recommend skipping the soy protein and opting for an
isoflavone supplement instead."


To Your Health!
Dr. Stephen G Chaney
http://www.chaneyhealth.com/

These statements have not been evaluated by the Food
and Drug Administration. This information is not
intended to diagnose, treat, cure or prevent any
disease.