Isoflavones and Phytoestrogens
The Biological Effects of Phytoestrogens
Herman Adlercreutz MD of the University of Helsinki says there is "no evidence in the literature suggesting that phytoestrogens, present in amounts found in human foods, could have biological effects, or stimulate already existing cancer, and there is also no evidence that such phytoestrogens could initiate cancer." [Annals of Medicine 29: 95-120, 1997]
Why get so bothered about soy? Indeed, spices such as thyme, oregano and turmeric bind with estrogen or progesterone and are thus known to be hormone blockers. [Proceedings Society Experimental Biology Medicine 21: 369-78, 1998]
Soybean compounds such as IP6- phytic acid, protease inhibitors and isoflavones, among others, appear to reduce the incidence of colon, prostate and breast cancer. [Journal Nutrition 125: 733-743S, 1995]
Science backs the consumption of soy protein and/or soy extracts (phytoestrogen-isoflavones) for males with prostate tumors.
In immune-depressed rodents whose prostate glands were inoculated with human cancer cells, soy significantly reduced the size of tumors and the number of blood vessels that feed tumors. [Journal Nutrition 129: 1628-35, 1999]
Recent data shows that neither soy, nor soy isoflavones, exert estrogenic effects on vaginal or breast tissues in postmenopausal females. [Journal Clinical Endocrinology 84: 3479-84, 1999]
In monkeys, soy phytoestrogens reduced cholesterol but did not affect the reproductive hormones. [Journal Nutrition 126: 43-50, 1996]
There is a great difference between animal and human studies.
Soybean cereal has been shown to interfere with the growth of young rodents. [Medicina 59: 747-52, 1999]
But in infants, there was no difference noted in weight gain nor pancreatic enzyme production when fed soy or whey protein formula. [Scandinavian Journal Gastroenterology 32: 273-77, 1997]
Be wary of so-called experts who only quote animal data to support their claims that soy is toxic or unhealthful.
The natural health gurus are correct on one point. Soy is being over-promoted by billion-dollar companies that grow the beans.
Estrogenic compounds are found in other natural foods such as alfalfa sprouts and sunflower seeds, but they aren't being aggressively marketed by multi-national agricultural companies.
A recent study conducted among 31 patients with high cholesterol, who were provided 33 grams per day of soy protein (providing 86 mg of isoflavones), reveals that LDL "bad" cholesterol levels were significantly reduced even among subjects who were already taking vitamin E supplements (400-800 IU).
The soy protein did not increase the risk of hormone-induced cancers. [Metabolism 49: 537-43, 2000]
Stephen Holt, MD, writing in Natural Pharmacy, has done the best job of sorting out information about soy. He says soy protein should be distinguished from the soy extracts or "isoflavones".
Consumption of up to 120 milligrams of soy isoflavones from soy foods should not be considered worrisome. He says phytoestrogens in soy are far weaker than the potent synthetic or natural estrogens commonly prescribed to women for menopause symptoms.
But he does caution against excessive consumption of soy isoflavones in "food supplements" or from fermented sources (tempeh, miso) which Fallon and Enig advocate. His guess is no more than 45 milligrams of conjugated isoflavones from fermented or supplmental sources daily. [Natural Pharmacy, April 2000]
While soy has gained the most attention because it is backed by powerful agribusiness, its cousin lignan may soon become a more desirable phytoestrogen.
Herman Adlercreutz, one of the world's top isoflavone researchers, emphasizes the importance of other phytoestrogens.
"Don't forget the lignans," he says. [Nutrition Science News] We can see why researchers are turning their attention to lignan.
Lignan is a normal component of the diet, albeit it is only consumed in small amounts.
Lignan is most abundant in flaxseed. Lignans in flaxseed have been compared to Tamoxifen, a hormone-blocking drug often prescribed in cases of breast cancer. [Cancer Letters 125: 69-76, 1998] Adlercreutz says the areas of the world where consumption of isoflavones and lignans are high have low rates of prostate, breast and colon cancer.
Animal experiments confirm that lignans and isoflavones prevent cancer in blood vessel disease. [Annals Medicine 29: 95-120, 1997]
When rates of disease are investigated by the type of phytoestrogen, both isoflavones derived from soy, and lignans found in flaxseed, whole-grain rye bread, berries and some vegetables, are attributed to the reduction in breast, prostate and colon cancer. Where consumption of lignan is low (USA, Finland, Sweden, Australia) breast cancer levels are high. [Baillieres Clinical Endocrinology Metabolism 12: 605-23, 1998]
In one study prostate tumor cells were injected into rodents who were placed on different diets.
Only 50% of the sites injected with tumor cells grew tumors among the animals on soy, and only 30% of injection sites exhibited tumors among the animals that consumed lignan-rich rye bran.
The tumors that did grow were smaller in the animals consuming soy and rye bran and there was less secretion of prostate specific antigen (PSA). The addition of fat to the rye bran diet reduced its protective effect against prostate cancer. [Prostate 42: 304-14, 2000]
In a study where rodents were given a tumor-promoting agent, a diet enriched in soy did not reduce the number of colon tumors (1.38 tumors per animal) compared to a diet low in soy isoflavones (1.36 tumors per animals. But a lignan-rich rye bran diet did reduce the number of tumors! (0.17 tumors per animal). [Carcinogenesis 20: 927-31, 1999]
Summary
- Soy is not hemlock. It is not a toxin, nor does it contain toxins.
- Soy is like table salt. Overuse can be troublesome.
- Learn to use it sparingly.
- If you are looking for lignans in your diet, throw in some flaxseeds, or cold-pressed lignan-rich flaxseed oil. Lignan may soon create a greater stir among health advocates than soy.
Bill Sardi, Health Reporter, Knowledge of Health
www.tldp.com/issue/11_00/joysoy.htm
Related Articles
- The Importance of Nuts and Seeds in Your Diet [Read] [Leer]
- Studies Show Effects of Hydrogenated Trans-Fats on The Body. [Read] [Leer]
- More articles here.
