Naturally occurring substances called phytoestrogens, found in soy, flaxseed and other foods, do not seem to prevent breast cancer in Western women, researchers from the Netherlands report.
Phytoestrogens, which are estrogen-like plant substances, come in three main varieties: isoflavones, lignans and coumestans. Because women in Asia, whose diets are high in isoflavone-rich soy foods, are much less likely to get breast cancer than women in Western countries, there has been great interest in finding out whether phytoestrogens play a role in preventing breast cancer.
Some studies have linked soy consumption with a reduced risk of breast cancer in Asian women, but others have not. But a link between soy and a reduced risk of breast cancer has not been found in Western women.
Women in Western countries eat much less soy than their Asian counterparts, so detecting an effect may be difficult. Western women do consume isoflavones from other sources, however. They also consume lignans, which are found in seeds, whole grains, berries, fruits, vegetables and nuts.
A research team from the University Medical Center Utrecht looked for a connection between phytoestrogens and breast cancer risk in more than 15,000 Dutch women in a breast cancer-screening program. The women, who were between the ages of 49 and 70, were followed for an average of about 5 years.
The results of the present study, which focused on Western women whose habitual diet is low in phytoestrogens, showed no protective effects of isoflavones or lignans against breast cancer. Women who reported eating the most isoflavones were no less likely to develop cancer than women who ate the least. Breast cancer was less likely in women who ate the most lignans, but this reduction was not statistically significant.
At present, scientific research does not support increasing phytoestrogen intake among U.S. women to Asian levels, nor does it suggest that the typical phytoestrogen intake is problematic for healthy women.
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