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- Published: Tuesday, 27 September 2016 05:51
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What are phytoestrogens?
The major phytoestrogen groups are isoflavones, flavones, coumestans and lignans. The former three are flavonoids. Isoflavones are found in high concentration in soy bean and soy bean products (eg. tofu) where as lignans are mainly found in flax seed.
What is the effect of eating soy on women's hormone levels and growth within the breast?
Soy phytoestrogens could change breast cancer risk by changing the production and/or breakdown of reproductive hormones such as estrogen. The results of studies examining hormone changes among women eating soy have not been consistent, but recent studies suggest there may be a small decrease in the levels of estrogens in the body. Some studies have also shown that eating soy phytoestrogens is associated with a decrease in the formation of forms of estrogens that may directly lead to cancer causing mutations. Higher exposure to estrogens over a lifetime is linked with increased breast cancer risk. (See BCERF Fact Sheet #10, What Factors Might Affect a Woman's Exposure to Estrogen).
One of the ways higher estrogen exposure may be linked to breast cancer risk is through its ability to increase growth of milk ducts in the breast. Most breast cancer arises from these ducts. Several but not all studies examining the effect of soy phytoestrogens on breast growth in women have suggested that phytoestrogens have a weak estrogen-like effect. The longest examination followed 28 women for a year. These women received a soy supplement for six months. While they were taking this supplement the women were found to have more growth of the milk ducts in their breasts. These studies are not conclusive, but such growth could increase breast cancer risk. More study is needed to evaluate the possible effects of soy phytoestrogens on growth within the breast and hormone levels in the body.
What other effects do phytoestrogens have?
Other studies indicate they may have some health benefits including potential reduction in prostate cancer and cardiovascular disease risks, possible protection against osteoporosis (bone loss) and menopausal symptoms. Besides, both flavonoid and lignan phytoestrogens have antioxidant activity.
What foods contain phytoestrogens?
Estrogen is available in medically formulated pills. However, dietary estrogen (phytoestrogen) can be also found in wide variety of food products (including herbs), even though the level varies depending on the source. Below is a short list of phytoestrogen food sources analyzed by researchers in Canada. The Canadian researchers analyzed 121 food samples, of which the food samples with the highest total phytoestrogen content are presented below. The food samples with the highest total phytoestrogen content were nuts and oil seeds followed by soy products.
Total phytoestrogen content presented below is the sum of isoflavones (genistein, daidzein, glycitein, formononetin), lignans (secoisolariciresinol, matairesinol, pinoresinol, lariciresinol), and coumestan (coumestrol).
Table 1. Foods high in phytoestrogen content.
|Phytoestrogen food sources||Phytoestrogen content (µg/100g)|
|Mung bean sprouts||
Table 2. Total phytoestrogen and lignan content in vegetables, fruits, nuts and drinks.
|Food items||Lignan content (µg/100g)||Total phytoestrogen (µg/100g)|
|Soy bean sprouts||2.2||789.6|
|Nuts and other legume seeds|
|Black bean souce||10.5||5330.3|
Should you eat phytoestrogens if you are pregnant or breast-feeding?
Pregnant or breast-feeding women should not use phytoestrogen supplements or consume substantial amounts of flaxseeds on a regular basis. In animal studies, the phytoestrogens found in high amounts in flaxseeds have been shown to cause developmental abnormalities and some studies of soy phytoestrogens have shown a possible increase in susceptibility to cancer in offspring. Eating moderate amounts of soy or flax products should present no problem. Women in China and Japan regularly eat foods containing soy phytoestrogens during pregnancy and while breast-feeding and no adverse health affects have been reported in these countries.
Milder, I. E. J., Arts, I. C. W., Van de Putte, B., Venema, D. P., and Hollman, P. C. H. 2005. Lignan contents of Dutch plant foods: a database including lariciresinol, pinoresinol, secoisolariciresinol, and matairesinol. British Journal of Nutrition, 93:393-402.
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