Cancer Protection with Soy

Dietary soy appears to protect againts some cancers. In laboratory studies, genistein slows the growth of breast, prostate, colon and skin cancer cells.

Breast Cancer - Japanese women have about one quarter the risk of breast cancer of American Women. A Singapore study found that premenopausal women eating the most soy foods had 60 percent less breast cancer risk than those with the lowest intake; a Japanese study found that premenopausal women with the highest tofu intake had 20 percent less risk.

However, in both studies ther was no benefit for posmenopausal women. Studies of Western women are not definitive because soy intake is very low but there is some evidence that if young women eat soy it may protect them later life. Soy intake need to be considered carefully in women with existing benign breast growth or breast cancer because remilinary studies have shown it may have undesirable oestrogenic effects on breast tissue. No firm consclusion can be drawn until further research is conducted.

Prostate Cancer - Soy has been inplicated in the low rate of deaths from prostate cancer in Japan. Genistein may inhibit the enzyme that stimulates prostate cell growth and can slow the growth and spread of prostate cancer cells in the laboratory.

Animal studies have found that soy or genistein slows the growth of prostate tumours. In a small study of men with prostate cancer in which conventonal treatment was ineffective and prostate specific antigen (PSA), a cancer activity marker, was increasing, 120 mg of soy isoflavones daily for six months lessened the PSA rise. However, other studies show no effect on PSA levels.