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| |  DG DISPATCH - BREAST CANCER: Jury Still Out On Plant Estrogens By Robert Carlson Special to DG News SAN ANTONIO, TX -- December 9, 1999 -- Although many women have begun adding soy products to their diets to prevent breast cancer, there is no clear-cut evidence that estrogens from plants, such as soy, actually have a protective effect.
A few studies have even found that phyto-estrogens promote cancer, says Walter Willett, MD, DrPH, Chairman of the Department of Nutrition and Professor of Epidemiology and Nutrition, Harvard School of Public Health, in Boston, MA. "We do not know if plant estrogens increase or decrease risk," Dr. Willett said in the opening plenary lecture at this meeting. "The evidence in the literature is mixed and not enough women have been using soy products until lately." Estrogens are definitely a key factor in breast-cancer development, though. Dr. Willett said the risk of having the disease is lower among women who begin menstruating at a later age and in those who have had children, because their ovaries produce estrogen for fewer years. But breast cancer development is a complicated process, he said. It is not clear whether plant-derived estrogens replace the body’s natural estrogens and therefore reduce the risk of cancer, or if they augment the natural estrogens and perhaps promote cancer. Even if soy-derived estrogen proves beneficial, dietary changes alone are not likely to reduce high levels of natural estrogen in women who are at risk of developing breast cancer, Dr. Willett said. He predicted that, some day, women who have close family relatives with breast cancer - or who have other strong risk factors - will take estrogen-blocking drugs such as tamoxifen or raloxifene to reduce risk of breast cancer, just as people now take cholesterol-blocking “statin” drugs to reduce the risk of heart disease. Dr. Willett dismissed some other popular beliefs: -- Neither physical activity nor selenium supplements appear related to risk of breast cancer. He stressed, though, that exercise has many other important health benefits.
-- Higher fat intake does not increase risk of breast cancer, he said, even though this has been speculated for years. There is clearly an association between risk of heart disease and dietary fat intake, Dr. Willett said, but studies begun in the 1980s are just beginning to show that overall fat intake has very little affect, if any, on the risk of developing breast cancer. -- There is a slight trend towards protection from eating monosaturated fats, he said, and a few studies from Europe point to a possible protection from olive oil. -- Weight gain and the use of oral contraceptives do influence cancer risk. Dr. Willett cited a 1998 study showing that women who maintain their weight close to what they weighed at age 18, and who never take birth control pills, have the lowest risk of breast cancer.
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