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.
There is limited suggestive evidence that soy foods may lower the risk of prostate and stomach cancer. The evidence for soy foods and cancer of the pharynx, oesophagus, pancreas, breast and endometrium is limited with no conclusion possible. 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.
This position statement describes phyto-oestrogens and explains why Cancer Council supports the consumption of soy foods in the diet.
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.
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.