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Phytoestrogens are a group of compounds derived from plants which are used primarily for estrogen hormone replacement for women in menopause. The three highest rated food sources containing phytoestrogens are soy beans and flaxseed with tofu, made from soy, being the third. Because the isoflavones in soy and lignans in flaxseed are inherent in the foods themselves, the effects of phytoestrogens must be expanded to a look at the overall effects on the body of the foods themselves. Although beneficial effects of phytoestrogens have been seen in regards to the treatment of menopause, there are some side effects which have been noted and caution should be taken by those who use these foods as a therapeutic treatment 2.


Sally Fallon & Mary G. Enig, Ph.D., author and nutritionist report in an article on naturopathic doctor Joe Mercola’s health news site about how soy isoflavones may reduce the effectiveness of the thyroid gland and its production of thyroid hormones contributing to hypothyroidism 1.

Decreased Mineral Absorption

The Benefits and Drawbacks of Soy Protein Powder in Women

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Soybeans have particularly high levels of phytic acid, notes the Fallon and Enig article, preventing proper absorption of minerals such as:

  • calcium
  • magnesium
  • iron
  • copper,
  • zinc


Breast Cancer

Soy and Hormonal Imbalance

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Kirk Williams, Masters’ student of Pharmacology from Tulane University discusses concerns that eating soy products may increase the risk of breast cancer in woman who are sensitive to hormone replacement therapy and possibly allergic to soy. Furthermore phytoestrogens may reduce the effectiveness of tamoxifen, the breast cancer medication and those woman taking tamoxifen should avoid eating soy.

Gastrointestinal Effects

Flaxseed is high in fiber and causes the usual side effects in people not used to ingesting high fiber with their meals 2.

The isoflavone genistein found in phytoestrogens from soy is known to cause stomach and other gastrointestinal problems including the erosion of the stomach lining from eating large quantities of soy products.