Soy Extract Does Not Prevent Uterine Thickening
December 18, 2003—A soy extract with protein and isoflavones does not protect postmenopausal women using estrogen from endometrial hyperplasia, according to a new study published in Menopause (2003;10:456–64).
Estrogen-replacement therapy has been demonstrated to effectively relieve menopausal symptoms such as hot flashes and vaginal dryness, to prevent bone loss, and to reduce the risk of colon cancer. Women using estrogen without progesterone after menopause are at high risk of developing endometrial hyperplasia (thickening of the lining of the uterus) that can progress to uterine cancer. There is no increased risk of endometrial hyperplasia and uterine cancer when estrogen is combined with progesterone; however, progestins, which are used as the progesterone-like substance in most hormone-replacement protocols, can increase the breast cancer-causing effect of estrogen.
Soy is a well-known source of plant substances known as phytoestrogens, which have some estrogen-like effects in the body. Studies have shown that soy extracts containing both isoflavones (the major phytoestrogens in soy) and protein can reduce the symptoms of menopause without increasing the risk of endometrial hyperplasia. Test tube and animal studies have found that soy extracts can prevent estrogen-induced endometrial hyperplasia and uterine cancer, and reduce the carcinogenic effect of estrogen on the breasts.
In the current study, 30 healthy post-menopausal women were randomly assigned to receive one of four daily treatments: group one received 0.5 mg of estradiol and 38 grams of placebo powder, group two received 1.0 mg of estradiol and 38 grams of placebo powder, group three received 0.5 mg of estradiol and 38 grams of soy-extract powder, and group four received 1.0 mg of estradiol and 38 grams of soy-extract powder. The placebo powder was made from dairy protein and the soy extract contained 25 grams of protein and 120 mg of isoflavones. Both powders were mixed into a beverage for consumption. After six months of treatment, all four groups were found to have endometrial hyperplasia. The two groups receiving the soy extract had slightly less endometrial thickening than the groups receiving placebo but the differences between groups did not reach statistical significance. Further investigation revealed that the rate of bone loss was similar in all four groups.
The results of this preliminary study suggest that a soy extract containing protein and isoflavones does not protect postmenopausal women from the harmful effects of unopposed estrogen on the uterus. A larger study is needed to determine whether the slight benefit found in the soy groups was real or merely due to chance. This study also shows that soy does not interfere with or enhance the beneficial effect of estrogen on the bones.
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Maureen Williams, ND, received her bachelor’s degree from the University of Pennsylvania and her Doctorate of Naturopathic Medicine from Bastyr University in Seattle, WA. She has a private practice in Quechee, Vermont, and does extensive work with traditional herbal medicine in Guatemala and Honduras. Dr. Williams is a regular contributor to Healthnotes Newswire.
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