Melbourne Holistic Health Group

Published in Articles - Soy on 09 October 2011 by Melbourne Holistic Health Group

There is a great deal of confusion about the safety of soy for women either with breast cancer or having breast cancer risk, primarily based on the mistaken belief that because soy contains oestrogen-like compounds called phyto-oestrogens, that it can stimulate breast tissue like our own body’s oestrogen or pharmaceutical oestrogen. Soy beans and products made from soy beans contain a class of phyto-oestrogens called isoflavones. Research has shown that consumption of soy in the diet, in amounts equivalent to that in an Asian diet is not only safe but actually reduces the risk of breast cancer and does not increase the risk of breast cancer recurrence in women who have had breast cancer.

Where this confusion stems from is that phyto-oestrogens do bind to oestrogen receptors (ER). Previously it was assumed that this binding stimulated beast tissue proliferation, making phyto-oestrogen intake unsafe. Understandably, this lead to the belief that ‘soy is bad for you’. But, the activity of phyto-oestrogens is influenced by the oestrogen environment, how they bind to the oestrogen receptor and particularly to which oestrogen receptor they bind to. Different types of oestrogen receptors have been discovered and this information has assisted us to understand how soy foods can actually assist in providing protection from breast cancer.

The 2 oestrogen receptors of interest here are oestrogen receptor alpha (ER-α) and oestrogen receptor beta (ER-β). The oestrogen produced by the ovaries binds to both oestrogen receptors with equal ability. Binding to ER-α stimulates growth of hormone-sensitive tissue. For example, the processes involved in the normal menstrual cycle are activated by oestrogen’s interaction with ER-α. These receptors are also related to the growth of hormone-sensitive tumours such as breast and endometrial cancer (or prostate cancer in men).

ER-β has functions distinct from ER-α and seems to counteract processes brought about by ER-α. Isoflavones, found in soy as well as in other legumes and red clover, can bind to both ER-α and ER-β, but they preferentially bind to and activate ER-β. Because of the preferential binding of isoflavones to ER-β, which is a natural counterplayer to the ER-α-mediated hormonal effects, activation of ER-β by isoflavones protects tissues including breast tissue from excessive oestrogenic effects. Therefore soy helps to protect breast tissue. For this reason, isoflavones found in soy are sometimes classified as selective (o)estrogen receptor modulators (SERMs).

Research into phyto-oestrogens and breast cancer has shown:

• There was a small reduction in the risk of breast cancer associated with phyto-oestrogen consumption such as soy. Pre-menopausal women obtained more benefit in terms of lowered risk than post-menopausal women when they consumed soy
• Phyto-oestrogen consumption prior to the onset of puberty may be THE important factor in gaining the anti-cancer effects of phyto-oestrogens in later life. Researchers found that women who consumed a moderate amount of soy throughout their lives had a lower breast cancer risk compared to women who did not consume soy and this protective effect may have been due to pre-puberty soy intake
• A moderate consumption of soy isoflavones from foods such as soy did not increase the risk of breast cancer recurrence in Western women, and Asian women who had had breast cancer had a better prognosis if they continued eating soy foods.

In summary, there is no evidence to suggest that eating soy foods in amounts consistent with an Asian diet is detrimental to breast health and that such a diet increases breast cell growth in either pre- or post-menopausal women with or without a history of breast cancer, as this amount of soy does not result in adverse stimulatory effects on breast tissue.

Additionally, phyto-oestrogen foods also have anti-cancer effects related to their non-oestrogen-like actions, which appear to be important. For example, soy isoflavones can also act as antioxidants, which may contribute to their anti-cancer properties.

Soy supplements

Foods that are rich in isoflavones like soy, appear to confer protection against breast cancer whilst some isolated and highly processed individual isoflavones may stimulate breast cells (depending on dose). We therefore recommend that women who are breast cancer survivors or are at high risk of developing breast cancer do not consume highly processed soy products such as soy protein isolate, isoflavone-rich soy extracts or isoflavone capsules. Soy germ may be an exception as it very similar to whole soy and you should discuss its suitability for you with your naturopath.

Reference
Trock, BJ et al 2006. ‘Meta-Analysis of Soy Intake and Breast Cancer Risk’ J of the National Cancer Institute 98 (7), pp 459-471)

Other articles on soy:

• Types of Soy Products
• Can soy help hot flushes?
• How can soy help prevent cardiovascular disease?
• Tofu recipes