There is evidence both from animal studies and epidemiological studies on humans that phytoestrogens have a protective effect against cancer.
Asian populations consuming diets high in the phytoestrogens found in soybeans have lower incidences of hormone-dependent cancers (including breast, ovarian, and endometrial cancers) compared to western populations. Also, the prevalences of osteoporosis and menopausal symptoms are lower. In addition, the incidence of coronary heart disease is lower in Asian populations. However, when Asian populations immigrate to western countries and adopt western diets, the risk for those diseases rises.
A survey of a variety of populations of women showed that urinary phytoestrogens (a measure of phytoestrogens in the diet) are highest among vegetarians, particularly macrobiotics, and lower among breast cancer patients, suggesting an association between low disease risk and high phytoestrogen intake.
Many studies in cell cultures and in rats and mice and nonhuman primates have suggested that phytoestrogens have a protective effect against tumor growth. The way phytoestrogens protect against tumor growth varies depending on the cancer type and the individual compound. Some phytoestrogens act by competing with endogenous estrogen for receptor sites, while others act by inhibiting enzymes involved with cancer formation. Enterolactone inhibits breast cancer cell proliferation in the presence of estradiol, but alone it stimulates proliferation. Their action also can be different in cell culture than it is in the whole animal: genistein is toxic to prostate cancer cells, but fails to inhibit prostate cancer growth in primates.
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Prepared Summer 1997 by Bernadene Magnuson, Ph.D.
University of Idaho, Dept. of Food Science and Toxicology - EXTOXNET FAQ Team.