Understanding Isoflavones
Isoflavones are members of a large group of compounds called phytochemicals. Found only in plants, phytochemicals are not considered nutrients – that is, they are not necessary to support life. However, many of these compounds may 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. In other cases, isoflavones act as anti-estrogens, and may help reduce certain negative symptoms or risk factors associated with estrogen. Isoflavones also have many beneficial physiological effects that have nothing to do with estrogen at all. For instance, isoflavones are thought to be potent antioxidants.
Soy foods and Isoflavones
There are very few dietary sources of isoflavones. In fact, soybeans and other soy foods such as soy milk are the only commonly-consumed foods that provide relevant quantities of isoflavones. Many non-Asian Americans don’t consume soy products or soy supplements, and therefore have extremely low intake 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 soyfoods are prevalent.
Isoflavones and Health
The U.S. government is currently funding extensive research into 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 risk for heart disease.(1)(2) They may also inhibit certain negative effects of LDL-cholesterol (“bad” cholesterol), making the LDL-cholesterol less damaging to arteries.(3)(4)
- Bone health: Studies in Asia reveal a link between isoflavone intake and greater bone mineral density – a measure of how strong bones are.(5) Also, 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.(6) Clinical studies, in which researchers can control the amount of isoflavones consumed, also suggest that isoflavones support bone health. Several long-term studies are currently underway to build upon these findings. While conclusive results are still years away, data thus far is 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.(7)
- 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.(8) Promising animal studies suggest that isoflavones are responsible for this proposed benefit.
- Prostate Cancer: 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.(9) Consumption of isoflavone-rich soy foods may be one reason why prostate tumors grow slowly in Japanese men, and are less likely to become life-threatening.
Getting Isoflavones in Your Diet
Traditional soy foods such as soy milk and tofu are the most reliable sources of isoflavones. Because the concentration of isoflavones in soybeans varies from crop to crop and from year to year, soyfood labels typically do not carry specific information about isoflavone content, and it is impossible to determine precise content without lab analysis. However, for a rough approximation, you can estimate the milligrams of isoflavones in a natural soy food such as Silk® Soymilk by multiplying the grams of protein by 3.5. This guideline may not apply to heavily processed soy foods or those made with soy protein isolate, because some processing methods reduce isoflavone content.
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 risk for certain chronic diseases. In addition to these proposed isoflavone benefits, soy foods like Silk Soymilk also provide plenty of cholesterol-free soy protein, abundant calcium, vital antioxidants and many other nutrients that make good sense for your healthy lifestyle.
1. 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.
2. 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.
3. 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.
4. 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 U S A 1998;95(6):3106-10.
5. 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.
6. 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.
7. Krebs EE, Ensrud KE, MacDonald R, Wilt TJ. Phytoestrogens for treatment of menopausal symptoms: a systematic review. Obstet Gynecol 2004;104(4):824-36.
8. 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.
9. 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.