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Phytoestrogens

Phytoestrogens are plant molecules that have structural similarity to our own endogenous estrogens. The main categories of found in plants are:

  • Isoflavones (i.e. genistein, diadzein, biochanin A & formononetin)
  • Lignans
  • Coumestans
  • Triterpenoid & Steroidal Saponins
  • Resorcyclic acid lactones

It is important to note that these naturally occurring plant compounds are very different from xeno-estrogens, which include many pesticides, agricultural chemicals, hormones used to treat animals or fish, polychlorinated biphenols (PCBs), plastics and paints, which can have potentially harmful effects on our health.

How do Phytoestrogens Work? 

Phytoestrogens can bind with estrogen receptors in the body, however they are generally up to 400 times smaller than endogenous estrogens (those which are made by the body), and are much weaker in their activity & biological effects.

Phytoestrogens are anti-estrogenic in pre-menopausal women and in cases of estrogen dominance because they are competitive antagonists of estrogen receptor sites (i.e. they fill the site and prevent or block endogenous estrogen from working at the receptor site, but the effect of the plant estrogen is much weaker). In peri and post-menopausal women they are estrogen synergists because even the slight stimulus from the plant molecule is greater nothing, and the phytoestrogen can summate with residual endogenous estrogen.

They can also stimulate hepatic production of SHBG (sex hormone binding globulin) which serves to reduce the availability of androgens to undergo aromatization, inhibiting the enzyme aromatase enzyme which is responsible for the biosynthesis of endogenous estrogens.

  • Isoflavones are converted to diadzein in the plants and then to equol by our intestinal flora. Equol is the strongest of the phytoestrogens but still about 1000 times weaker than estradiol. Biochanin A is converted to genistein which is about 100,000 times weaker than estradiol.
  • Lignans are converted by our bowel flora into active forms know as enterolactone & enterodiol.
  • Saponins have structural similarity to cholesterol and hence to hormones manufactured from cholesterol including estrogens, progesterone, androgens and glucocorticoids (cortisol). Steroidal saponins must first be hydrolysed into the aglycone or sapogenin by bowel flora before they are biologically active. Their binding capacity is considered very weak with endogenous estrogens.  

Applications of Phytoestrogens

Are notable cancer-preventatives by virtue of reducing the effects of endogenous estrogens. This is especially true in pre-menopausal women and obese post-menopausal women where peripheral aromatisation of androgens to estrogen is high.

Coumestans inhibit bone resorption and promote bone remineralization in laboratory experiments and may be useful in preventing and treating osteoporosis.

Saponins with steroid-like structure act as potent anti-inflammatories and cause an indirect estrogenic effect by modification of the hypothalamic – pituitary – ovarian axis and can be helpful in treating PCOS.  May act through modulation of hypothalamic – pituitary – ovarian axis and potentiation of ovarian hormones as well to reduce hot flashes in post-menopausal women without increasing estradiol, indicating an effect on the hypothalamus.

Herbal Examples

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