What are isoflavones?

isoflavones structureIsoflavones are phytochemicals, which are compounds found only in plants. They are a type of phytoestrogen because they resemble human estrogen in chemical structure but their biological action is a lot weaker. By mimicking human estrogen at certain sites in the body, isoflavones provide many health benefits that help you to avoid disease. By blocking estrogen receptors they can act as anti-estrogens but they can also function as weak estrogens. Isoflavones are found in soybeans, chick peas and some other legumes. However, soybeans are unique in that they contain the highest concentration of these powerful compounds. The most important isoflavones found in soybeans are genistein and daidzein.

Health effects of isoflavones

Lower cancer risk - Epidemiological studies have suggested that Asian diets may provide protection from several cancers, including those of the breast, prostate gland and colon. The action of isoflavones as weak estrogens allows them to bind to estrogen receptors and block some of the detrimental effects of estrogen - such as promotion of cancer cell growth. Tamoxifen, a prescription drug for treating breast cancer, is though to act as an anti-estrogen by binding to the estrogen receptor and "blocking" the growth-promoting effects of estrogen in cancer cells. Women using tamoxifen have a lower incidence of breast cancer and a 30-40% reduction in breast cancer cell growth rate. The isoflavones in soy are chemically similar to tamoxifen and, therefore, may also reduce the risk of hormone-dependent cancers via the same "estrogen-blocking" mechanism.

Improved bone health - Isoflavones consumption has been shown to reduce bone loss and slow calcium loss in an animal model of osteoporosis, suggesting a possible beneficial role in preventing osteoporosis in humans. In addition, soybeans contain a relatively high calcium content. It is also interesting to note that soy protein seems to cause less loss of calcium from the body compared to other dietary sources of protein, which may promote calcium loss and bone breakdown at high levels. Ipriflavone, a synthetic isoflavone drug prescribed in Europe, is metabolized in the body into daidzein, and has potent effects on reducing bone resorption in post-menopausal women.

Relieves menopause symptoms - Soyfoods which contain isoflavones may help in the treatment of menopause symptoms. In women who are producing little estrogen, phytoestrogens may produce enough estrogenic activity to relieve symptoms such as hot flushes. From an epidemiological point of view, it is interesting that in Japan, where soy consumption is very high, menopause symptoms of any kind are rarely reported.

Lowers cholesterol - Isoflavones possess anti-oxidant action, and not only help to decrease the bad LDL cholesterol, but also increase the beneficial HDL cholesterol.

Isoflavones in soy

Soy contains many isoflavones, but the most beneficial are genistein and daidzein (see structure on right). The soybean contains about 200 mg isoflavones per 100 g. Other plants contain a lot less isoflavones.

Isoflavones levels in some foods (per 100g):
Tempeh43.52  mg
Peas bean2.42  mg
Peanuts0.26   mg
Navy bean0.20  mg
Chickpeas0.10  mg
Lentils0.10  mg
Bread0.02  mg
Black bean0.00  mg
(Source:USDA-Iowa State University Database on the Isoflavone, Rel. 1.3 - 2002)