About Isoflavones

Isoflavones are members of a large group of compounds called phytochemicals. Found only in plants, phytochemicals are thought to promote health and reduce disease risk. There is increasing evidence that diets rich in phytochemicals may help protect against cancer, heart disease, rheumatoid arthritis, macular degeneration, Alzheimer's disease and other conditions.

Isoflavones are also referred to as phytoestrogens, or plant estrogens, because they have a chemical structure similar to the female hormone estrogen. However, isoflavones are not the same as estrogen. In some cases, isoflavones can mimic certain positive effects of estrogen, which may help to explain some of their proposed benefits.^{1, 2} In other cases, isoflavones act as anti-estrogens, and may help reduce certain negative symptoms or risk factors associated with estrogen.^{3, 4} Isoflavones also have beneficial physiological effects that are not related to estrogen at all. For instance, isoflavones have also been studied for their antioxidant potential.⁵

Soy foods and isoflavones

There are very few dietary sources of isoflavones. In fact, soybeans and other soy foods such as soy beverages are the only commonly-consumed foods that provide relevant quantities of isoflavones; and you can also get isoflavones from soy supplements. However, soy products or soy supplements are not common in the general sections of the population and many North Americans have low intakes of these beneficial compounds. In contrast, people in Japan consume about 25 to 50 milligrams of isoflavones per day - the amount found in approximately one to two servings of soy foods. Researchers have examined this discrepancy as a possible explanation for the comparatively low rates of certain diseases in Japan and other Asian countries where soy foods are prevalent.

Isoflavones and health

There is currently extensive research on the potential health benefits of isoflavones. These studies cover a variety of areas, including:

Heart disease

Isoflavones may improve the health of the lining of blood vessels, which can reduce the risk of heart disease.^{6, 7} They may also inhibit certain negative effects of LDL-cholesterol (the "bad" cholesterol), making the LDL-cholesterol less damaging to arteries.^{8, 9}

Bone health

Studies in Asia reveal a link between isoflavone intake and greater bone mineral density - a measure of bone strength ¹⁰. One study has shown that women in Shanghai, China who ate the most soy foods were one-third less likely to experience a fracture than Chinese women who consumed the lowest amount of soy.¹¹ Clinical studies, in which researchers can control the amount of isoflavones consumed, have also suggested that isoflavones support bone health. Several long-term studies are currently underway to build upon these findings. While conclusive results are still years away, the data thus far are encouraging.

Menopausal symptoms

Some studies have found a relationship between soy food consumption and reduced menopausal symptoms, such as hot flashes. While not all menopausal women experience these benefits, those suffering from frequent hot flashes typically gain significant relief when they include a source of isoflavones in their diet.¹²

Breast cancer

Scientists first hypothesized that soy foods may help reduce breast cancer risk when they noted the historically low rates of breast cancer in Asian populations. Current research is examining the possibility that consuming soy foods during adolescence reduces breast cancer risk later in life.¹³ Promising animal studies suggest that isoflavones are responsible for this proposed benefit.

Prostate cancer

Consumption of isoflavone-rich soy foods has also been linked to positive benefits regarding prostate cancer. It has been observed that prostate tumors grow slowly in Japanese men and the tumors are less likely to become life-threatening ¹⁴. To understand this relationship better, studies have been done in test tubes and in animals, whereby isoflavones have been shown to inhibit the growth of prostate cancer cells in test tubes and to slow the development of prostate tumors in animals.

Getting isoflavones in your diet

Traditional soy foods such as soy beverages and tofu are the most reliable sources of isoflavones.

A growing body of promising research indicates that consuming one to three servings of isoflavone-rich soy foods per day - as part of a balanced diet low in cholesterol and moderate in fat - may help to reduce the risk of certain chronic diseases. In addition to isoflavones, a soy food like Silk soy beverage also provides soy protein (which is cholesterol-free like all plant protein sources), an excellent source of calcium and many other nutrients that make good sense for your healthy lifestyle.

1. Kuiper GG, Carlsson B, Grandien K, Enmark E, Haggblad J, Nilsson S, Gustafsson JA. Comparison of the ligand binding specificity and transcript tissue distribution of estrogen receptors alpha and beta. Endocrinology 1997;138:863-870.
2. Kuiper GG, Lemmen JG, Carlsson B, Corton JC, Safe SH, van der Saag PT, van der Burg B, Gustafsson JA. Interaction of estrogenic chemicals and phytoestrogens with estrogen receptor beta. Endocrinology 1998;139:4252-4263.
3. Teede HJ, Dalais FS, McGrath BP. Dietary soy containing phytoestrogens does not have detectable estrogenic effects on hepatic protein synthesis in postmenopausal women. Am J Clin Nutr 2004;79:396-401.
4. Naciff JM, Jump ML, Torontali SM, Carr GJ, Tiesman JP, Overmann GJ, Daston GP. Gene expression profile induced by 17alpha-ethynyl estradiol, bisphenol A, and genistein in the developing female reproductive system of the rat. Toxicol Sci 2002;68:184-199.
5. Chen Y, Isoflavones improve plasma homocysteine status and antioxidant defense system in healthy young men at rest but do not ameliorate oxidative stress induced by 80% VO2pk exercise. Ann Nutr Metab 2005 Jan-Feb;49(1):33-41.
6. Colacurci N, Chiantera A, Fornaro F, et al. Effects of soy isoflavones on endothelial function in healthy postmenopausal women. Menopause 2005;12(3):299-307.
7. Squadrito F, Altavilla D, Crisafulli A, et al. Effect of genistein on endothelial function in postmenopausal women: a randomized, double-blind, controlled study. Am J Med 2003;114(6):470-6.
8. Wiseman H, O'Reilly JD, Adlercreutz H, et al. Isoflavone phytoestrogens consumed in soy decrease F(2)-isoprostane concentrations and increase resistance of low-density lipoprotein to oxidation in humans. Am J Clin Nutr 2000;72(2):395-400.
9. Tikkanen MJ, Wahala K, Ojala S, Vihma V, Adlercreutz H. Effect of soybean phytoestrogen intake on low density lipoprotein oxidation resistance. Proc Natl Acad Sci USA
1998;95(6):3106-10.
10. Messina M, Ho S, Alekel DL. Skeletal benefits of soy isoflavones: a review of the clinical trial and epidemiologic data. Curr Opin Clin Nutr Metab Care 2004;7(6):649-58.
11. Zhang X, Shu XO, Li H, et al. Prospective cohort study of soy food consumption and risk of bone fracture among postmenopausal women. Arch Intern Med 2005;165(16):1890-5.
12. Krebs EE, Ensrud KE, MacDonald R, Wilt TJ. Phytoestrogens for treatment of menopausal symptoms: a systematic review. Obstet Gynecol 2004;104(4):824-36.
13. Korde L FT, Wu A, et al. Adolescent and childhood soy intake and breast cancer risk in Asian-American women. Breast Cancer Res Treat 2005;88:S149.
14. Santibanez JF, Navarro A, Martinez J. Genistein inhibits proliferation and in vitro invasive potential of human prostatic cancer cell lines. Anticancer Res 1997;17(2A):1199-204.