Phytoestrogens

They can promote Cancer!

Do phytoestrogens prevent cancer?  The evidence to support the industry claim is scant and recent work indicates that phytoestrogens may actually increase the risk of breast cancer.  And HOT OFF THE PRESS is an article from Japan in which the author proposes a link between the soy phytoestrogen genistein and infantile leukemia.

 
Soy phytoestrogens causing cancer?  Hold on a minute what about all the latest research that tells us that soy prevents cancer?!  The key arguments in the case for soy as an anti-cancer foodstuff appear based on:
 
Crude epidemiology.  Mortality rates of certain types of hormone dependent cancers (such as breast and prostate) are lower in Asians.  Asians eat lots of soy.  Wow, if we eat lots of soy we will reduce our risk of cancer too!
Evidence that the soy isoflavone genistein displays anti-cancer properties in vitro.  Wow, genistein inhibits the growth of, and kills, cancer cells; let's eat more today!

But long before these anti-cancer claims became common, researchers had noted that phytoestrogens such as genistein could greatly enhance the proliferation of cancer cells.

Confused?  Well there's no need to be.  it is not uncommon for hormonally active agents, such as the soy phytoestrogens, to act as both estrogens and anti-estrogens. In simple terms this means that they can act to stimulate or inhibit the growth of certain types of cells, such as those found in the human breast.

How do we know whether a compound will have a tendency to stimulate or inhibit cell growth?  Well both natural hormones and hormonally active agents can work quite differently in people according primarily to dose and life stage.  Contrast adults with children; premenopausal women with menopausal or post-menopausal women; women with breast cancer with women with no abnormal breast tissue growth.

Hence, although you may have heard lots about studies showing the anti-cancer effects of soy you may not have read about the following work:

Short-term soy feeding increases breast proliferation in pre-menopausal women with a history of benign or malignant breast disease.
Postmenopausal women consuming soy isoflavones as a natural HRT may place themselves at greater risk of breast cancer. In 1996 Dr Nicholas Petrakis, University of California, San Francisco, reported that 'Prolonged consumption of soy protein isolate has a stimulatory effect on the premenopausal female breast, characterised by increased secretion of breast fluid, the appearance of hyperplastic epithelial cells and elevated levels of estradiol. These findings are suggestive of an estrogenic stimulus from the isoflavones genistein and daidzein contained in soy protein isolate'
In support of a precautionary approach to consuming soy to prevent breast cancer is Dr Bill Helferich of the University of Illinios. He has recently stated that 'there is potential for dietary genistein to stimulate the growth of estrogen-dependent tumors in humans with low circulating endogenous estrogen levels, such as those found in postmenopausal women'.
Dr Craig Dees of Oak Ridge National Laboratory has also found that soy isoflavones cause breast cancer cells to grow. He reported that 'low concentrations of genistein may stimulate MC-7 cells to enter the cell cycle'. Dees concluded that ' women should not consume particular foods (eg. soy-derived products) to prevent breast cancer'.
Dees has also found that xenoestrogens, such as genistein, significantly enhance risk for breast cancer during growth and adolescence.  Now there's a good reason to keep your teenage daughter off soy.
Work by Manfred Metzler has shown that genistein is clastogenic!  A clastogen is any substance which causes chromosomal breaks.

In reality there can be no blanket approach to cancer prevention and an agent that may reduce the risk of cancer in one person may increase the risk of cancer in another.

If you're still confused there are several other things that we'd like to make crystal clear:

It is completely irresponsible for the soy industry or isoflavone supplement manufacturers to promote (or even suggest) that their products are cancer preventing without: any reference to individual case history; any real idea of what constitutes a safe dose; or any mention of the fact that soy may increase the risk of cancer.
Those soy food or isoflavone supplement manufacturers that proclaim the anti-cancer properties of their products are guilty of giving false hope to millions; but worse they may be placing consumers at greater risk of contracting the same horrendous diseases they are trying to avoid.

Soy Online Service conclude that those on the 'soy prevents cancer' bandwagon are the lowest form of life on the planet.