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Nutrition Hot Topics - Soy & Breast Cancer Concerns
Soy
protein is naturally rich in compounds called isoflavones. Scientists refer to these compounds as phytoestrogens or estrogens
from plants. These compounds have chemical structures that resemble estrogen that the body makes. Phytoestrogens, however,
are much weaker in activity than the estrogen made by the body.The soy-breast cancer connection started with epidemiological
data showing that in countries where soy foods are common in the diet, breast cancer is relatively uncommon. This led researchers
to speculate that maybe it was the phytoestrogens unique to soy that help to prevent breast cancer. Laboratory studies support
this theory.The current thinking is that phytoestrogens may bind to estrogen receptors in tissues like the breast in place
of the more powerful estrogen the body produces. Because phytoestrogens have a much lower level of activity, the net effect
would be to lower the overall exposure to estrogen. If, over a lifetime, too much exposure to estrogen is a risk factor for
cancer, then the phytoestrogens in soy might actually help reduce cancer risk. Another possibility is that having phytoestrogens
around during puberty and early adult life (when breast cancers are probably initiated) may protect against cancer development.A
more controversial issue relates to the role of phytoestrogen compounds for women who have a history of breast cancer, especially
for women whose breast cancer is estrogen-receptor positive, meaning the cancer can be stimulated by estrogen. Estrogen medication
is contraindicated in these women because it could stimulate cancer recurrence. However, the effect of phytoestrogens in this
group of women is unknown. It is possible that these compounds might be protective against cancer recurrence. It's also theoretically
possible that they could have a stimulatory effect.This issue needs to be studied in long-term, randomized, controlled clinical
trials with thousands of women, some of which are now underway. Unfortunately, the only studies completed to date are small
trials that have examined the effect of phytoestrogens on breast cell proliferation. These studies have yielded mixed results.
Short-term studies seem to indicate that the phytoestrogens have an initial proliferative effect, which would not be good
if sustained. However, in longer-term studies, where scientists have studied a drug compound designed to act very similar
to phytoestrogens, the opposite effect occurs and proliferation is prevented.Some scientists and physicians feel that reasonable
consumption of soy protein and phytoestrogens are just fine for women with a history of breast cancer. In the absence of scientific
certainty, however, others recommend against the use of soy for women with a history of breast cancer. Since there is no definitive
science one way or the other, patients and physicians need to determine what is best.In summary, the bulk of the scientific
evidence favors a beneficial effect of soy consumption for the prevention of breast cancer. For women with a history of breast
cancer, the science isn't definitive.
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