The Consumer Guide to Soy Isoflavones
In This Guide... What is it? Soy isoflavones are phytochemical constituents of soybeans, a legume that has served as the basis for various foods in many Southeast Asian countries for thousands of years. The major isoflavones in soy are genistein and daidzein. Soyfoods also contain other valuable constituents, including protein, saponins, and phytosterols.
Benefits and uses: Genistein and daidzein have been
well researched by scientists for their antioxidant
and estrogenic properties. Isoflavones
may reduce the risk of hormone-dependent cancers, such as breast and prostate
cancer, as well as other
cancers. A review study
of soy research found that 65 percent of 26 animal-based cancer studies showed
a protective effect of soy or soy isoflavones.
Human research and population studies also suggest that soy can protect against
cancer as well as heart
disease. The mild estrogen activity of soy
isoflavones may ease menopause symptoms for some women, without creating
estrogen-related problems, and may help regulate hormone levels in premenopausal
women. Soy isoflavones may also
play a beneficial role in preventing osteoporosis and autoimmune conditions.
Daily requirement: There is no deficiency as such,
but people who do not consume soy
foods will not gain the benefits of soy.
Deficiency risk factors: Soy contains a compound called phytic acid that can interfere with mineral absorption.
Optimal intake: The ideal intake of soy is not known. Researchers suggest that the equivalent of one serving of soy foods per day supports good health, and the benefits increase as soy intake increases.
Food sources: High levels of soy-based isoflavones are found in roasted soy nuts, tofu, tempeh, soy milk, and some soy protein isolates. Other soyfoods include soy flour, miso, and soy sauce.
Safety: Soy products and cooked soybeans are very safe at a wide range of intakes. A small percentage of people, however, has allergies to soybeans and should, therefore, avoid soy products. Certain constituents in soy interfere with thyroid function but the clinical importance of this problem remains unclear.
What Is It?
Benefits and Uses
Daily Requirement
Deficiency Risk Factors
Optimal Intake
Food Sources
Recent Findings
Safety
What Types Of Soy Isoflavone Products Are Available?
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- Wei, H., et al., "Antioxidant and antipromotional effects of the soybean isoflavone genistein," Proc Soc Exp Biol Med (1995), 208:124–29
- Arora, A., et al., "Antioxidant activities of isoflavones and their biological metabolites in a liposomal system," Arch Biochem Biophys (1998), 356(2):133–41
- Messina, M.J., et al., "Soy intake and cancer risk: a review of the in vitro and in vivo data," Nutri Cancer (1994), 21:113–31
- Messina, M., "To recommend or not to recommend soy foods," J Am Diet Assoc (1994), 94(11):1253–54
- Menon, L.G., et al., "Effect of isoflavones genistein and daidzein in the inhibition of lung metastasis in mice induced by B16F-10 melanoma cells," Nutr Cancer (1998), 30(1):74–77
- Onazawa, M., et al., "Effects of soybean isoflavones on cell growth and apoptosis of the human prostatic cancer cell line LNCaP," Jpn J Clin Oncol (1998), 28(6):360–63
- Ishida, H., et al., "Preventive effects of the plant isoflavones, daidzin and genistin, on bone loss in ovariectomized rats fed a calcium-deficienct diet," Biol Pharm Bull (1998), 21(1):62–66
- Baum, J.A., et al., "Long-term intake of soy protein improves blood lipid profiles and increases mononuclear cell low-density- lipoprotein receptor messenger RNA in hypercholesterolemic, postmenopausal women," Am J Clin Nutr (1998), 68(3):545–51
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