The Cancer Council, New South Wales, Australia, has new guidelines on soy and cancer. Cancer Council recommends soy foods as part of a healthy diet but warn against high-dose supplements for people who have breast or prostate cancer.
Phyto-oestrogens are bioactive substances found in plant foods, with naturally occurring oestrogenic activity. Soy beans and other foods containing soy, such as tofu, tempeh and soy milk, are rich sources of phyto-oestrogens.
A high consumption of soy foods may lower the risk of breast and prostate cancers, but only a little. There is no association between soy foods and the risk of other cancers, including bowel cancer. While they may have a protective effect, there is also some evidence that phyto-oestrogens might stimulate the growth of existing hormone dependent cancers.
The Cancer Council supports the consumption of soy foods in the diet. This is consistent with Cancer Council recommendations and national dietary guidelines to eat a diet high in plant based foods. The Cancer Council does not recommend or support the use of supplements such as soy protein isolates or isoflavone capsules for healthy men and women to prevent cancer.
The Cancer Council does not recommend or support the use of supplements for breast cancer survivors. There is evidence to suggest that women with existing breast cancer or past breast cancer should be cautious in consuming large quantities of soy foods or phyto-oestrogen supplements.