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Soy isoflavones |
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| Soy isoflavones are a group of compounds found in and isolated from the soybean. Soy isoflavones are phytoestrogens which are plant-derived nonsteroidal compounds that possess estrogen-like biological activity. Isoflavones bind to estrogen receptors, affecting estrogen-regulated processes, and are therefore referred to as phytoestrogens (plant estrogens). Soy isoflavones are heterocyclic phenols with structural similarity to estradiol-17beta and selective estrogen receptor modulators. Isoflavones are a unique class of plant flavonoids that have a limited distribution in the plant kingdom and can be physically described as colorless, crystalline ketones. The most common isoflavone compounds are the conjugate, glucoside, and aglucone forms. The most common and important dietary source of these isoflavones are soybeans. Soy isoflavones comprise three main isoflavones and their glycosylated forms. The three main isoflavones are the aglycones genistein, daidzein and glycitein. Their glycosylated forms are called soy isoflavone glycosides which include genistin, daidzin, and glycitin. Isoflavones compounds, such as genistein and daidzein, are found in a number of plants, but soybeans and soy products like tofu and textured vegetable protein are the primary food source. |
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Health benefits of soy isoflavones |
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| Soy isoflavones have been a component of the diet of certain populations for centuries. Soy isoflavones have estrogenic, antioxidant activity. They may also have anticarcinogenic, anti-atherogenic, hypolipidemic and anti-osteoporotic activities. Soy isoflavones are powerful plant substances chemically similar to the female hormone estrogen. Soy isoflavones can be used alone to treat or
prevent breast cancer, prostate cancer, skin cancer, and colon cancer or as mechanism inhibitors. Isoflavones alone may also reduce or prevent various symptoms related to the onset and duration of menopause, including hot flashes and osteoporosis. Isoflavones alone may also be effective in certain cardiovascular applications, including heart disease, reducing cholesterol-lipid levels, modulating angiogenesis, and other vascular effects. Moreover, isoflavones alone have been implicated in reducing headaches, dementia, inflammation, and alcohol abuse, as well as immunomodulation.
Isoflavones acts as antioxidants to counteract damaging effects of free radicals in tissues. Isoflavones may reduce the risk of hormone-dependent cancers, such as breast and prostate cancer, as well as other cancers. By blocking enzymes thought to contribute to prostate cancer, soy isoflavones may delay or prevent its development. Isoflavones also have been found to have antiangiogenic effects (blocking formation of new blood vessels), and may block the uncontrolled cell growth associated with cancer, most likely by inhibiting the activity of substances in the body that regulate cell division and cell survival (growth factors). The soy isoflavone genistein has been reported to inhibit angiogenesis, the growth of new blood vessels that, when abnormal, can contribute to the development of cancer. Soy isoflavones have also been shown to inhibit 5 alpha-reductase, the enzyme that activates testosterone in the prostate gland and other tissues. Epidemiological studies have shown that populations with high intakes of soya foods, such as those of China, Japan and other Asian countries, usually have a reduced risk of cancers of the breast, prostate, colon and uterus.
Isoflavones can act like estrogen in stimulating development and maintenance of female characteristics or they can block cells from using other forms of estrogen. The mild estrogenic activity of soy isoflavones may ease menopause symptoms for some women, without creating estrogen-related problems. Soy may also be beneficial in preventing osteoporosis. Women approaching menopause who eat isoflavone-rich soy protein are significantly more likely to boost their bone mineral density than women whose diets are low in soy isoflavones. Soy isoflavones may help alleviate hot flashes and night sweats that many women experience during menopause.
The American Heart Association (AHA) recommends adding at least 25 grams of soy protein per day to a diet low in saturated fat and cholesterol to reduce the risk of heart disease. Soy isoflavones prevent LDL cholesterol from harming the walls of blood vessels by decreasing the formation of plaque in the vessel wall.
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Dietary sources of soy isoflavones |
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Isoflavone concentrations vary among soy products and among different brands of the same product. The highest levels are in whole bean products that have not been highly processed. Although many varieties of vegetables, grains, and legumes contain small amounts of isoflavones, by far the largest quantities are found in soybeans. Roasted soy nuts, tofu, tempeh, soy milk, meat substitutes, soy flour, and some soy protein isolates are also high in isoflavones. The soy germ, found in whole soybeans, is particularly high in isoflavones.In addition, the isoflavones present in soy are available as supplements, in capsules or tablets.
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Dosage, intake, recommended daily allowance (RDA) |
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No formal recommendations for isoflavone intake have been reported. Consumption of isoflavones in Asian countries varies between 25 and 200mg a day. In general, 250ml soya milk or yoghurt, or 50g soya flour, cooked soya beans or textured vegetable protein (TVP) provide approximately 50mg isoflavones. 2 grams of soy protein contains approximately 1 milligram of soy isoflavones. Most isoflavone supplements provide 25-100mg total isoflavones. The North American Menopause Society (NAMS) HAS reported that the consumption of 50 mg/day may reduce cholesterol, 40 to 80 mg/day may strengthen blood vessels and possibly improve blood pressure, 50 mg/day may keep bone health, and 40 to 80 mg/day may reduce hot flashes. |
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Side effects, overdosage symptoms, interactions |
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| Soy products are generally very safe. Common allergic side effects include stomach upset and digestive problems including constipation and diarrhea. Soy isoflavones have been reported to reduce thyroid function in some people. Soy products may worsen kidney stones, decrease thyroid hormone production, or increase the risk of bladder cancer. Pregnant women and nursing mothers should not use soy isoflavone supplements because of their estrogenlike effects. The phytoestrogen components of soy may interfere with the drug tamoxifen and raloxifene. High intakes of soy protein may interfere with the efficacy of the anticoagulant medication warfarin. A high-fiber diet may interfere with the absorption of soy isoflavones. |
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The primary benefit of soy comes from its isoflavone content. Isoflavones are antioxidants that combat damage caused by free radicals. In one study soy isoflavones reduced total cholesterol over 9% and LDL ("bad") cholesterol almost 13%. The level of HDL ("good") cholesterol increased over 2%. If you are battling high cholesterol, soy isoflavone may provide necessary support to lower cholesterol. Click here for more information.