Popular media would have us believe that plant constituents with a phenolic structure similar to oestrogen, known as phyto (plant) oestrogens, provide a natural alternative to the use of postmenopausal hormone replacement therapy.  Are the popular media right?
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Women experiencing mild menopausal symptoms may gain relief by dietary modification and lifestyle changes, such as reducing smoking and consumption of caffeine and alcohol, stress management, and increased exercise.  However, there is no evidence to support the belief that even a very high intake of soy products will alleviate hot flushes, night sweats, and other symptoms such as vaginal dryness, mood changes, and musculoskeletal symptoms.  No absolute conclusions can be drawn from the few studies of the effects of phytoestrogens on bone.  As with other interventions of unproved efficacy, long term randomised trials will be required to determine the place (if any) of phytoestrogens in the management of postmenopausal women.

http://www.mja.com.au/public/nutrition/women/wquest2.html
What is the role of phytoestrogens in treating menopausal symptoms?
Summary

• Most randomised placebo-controlled trials show no benefit of phytoestrogens in managing menopausal vasomotor symptoms. 
• Concentrated phytoestrogen supplements appear to have oestrogenic actions in the breast and may interfere with the therapeutic use of tamoxifen. 
• Unlike concentrated supplements, foods rich in phytoestrogens, such as vegetables, grains and legumes, are also excellent sources of fibre, unsaturated protein, vitamins and minerals and their consumption should be encouraged.



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It is essential that a distinction be made between nutrients consumed in food and as supplements taken as powders or pills. Women need to understand that the latter are not "natural" therapy, but rather pharmacotherapy, which can have adverse effects and should be evaluated with the same rigour as conventional pharmaceuticals. Phytoestrogens fall into this category, and taking phytoestrogen supplements as milk concentrate, flour or in tablet form can not be justified at this stage. There is no evidence that phytoestrogen supplements are more effective than placebo for relieving menopausal symptoms. Further, safety, particularly in terms of oestrogenic effects on the breast, has yet to be  established. Of specific concern is the use of phytoestrogen supplements in women who have had breast cancer, and potential interference with the therapeutic effects of tamoxifen.

Plants and botanicals that are reputed to have estrogenic activity include ginseng, fenugreek, licorice, sarsaparilla, gotu kola, wild Mexican yam, and dong quai. Phytoestrogens are defined as naturally
occurring plant sterols that may exert effects similar to estrogen. They fall into the following three groups: 

Isoflavones, particularly, genistein and daidzein <snip - see URL>

Lignans <snip - see URL>

Coumestans <snip - see URL>

Based on the information presented, isoflavone-containing soy foods may have favorable effects on the cardiovascular system, but major knowledge gaps still exist regarding effects of phytoestrogen supplements on bone diseases, various cancers, menopausal symptoms, and cognitive function.

The authors conclude that 12 weeks' partial substitution of omnivorous postmenopausal women with phytoestrogen-rich food increases their serum levels of SHBG. It may alleviate symptoms such as hot flashes and vaginal dryness. Long-term effects on bone density and heart disease remain to be determined.

However, there is some  evidence that isoflavones isolated from soy are less effective alone than when taken as part of a high-soy diet.

Soy products may impair thyroid function or reduce absorption of thyroid medication, at least in children. For this reason, individuals with impaired thyroid function should use soy with caution.

Conclusions: Although the observed health effects in humans cannot be clearly attributed to isoflavones alone, it is clear that foods or supplements that contain isoflavones have some physiologic effects. Clinicians may wish to recommend that menopausal women consume whole foods that contain isoflavones, especially for the cardiovascular benefits of these foods; however, a level of caution needs to be observed in making these recommendations. Additional clinical trials are needed before specific recommendations can be made regarding increased consumption of foods or supplements that contain high amounts of isoflavones.Menopause 2000;7:215–229. © 2000, The North American Menpause Society.)

Studies show red clover has no effect on symptoms of menopause
Sandra Coney looks at two new studies that debunk claims about phyto-oestrogens.
 

      Two new Australian studies have dented claims that the phyto-oestrogen isoflavone, found in the dietary supplement Promensil, is effective in relieving menopausal symptoms.

    Results from the two randomised placebo--controlled trials, published in the journal Climacteric failed to show a benefit.

    The rate of hot flushes between users of 40 mg or 160 mg dose Promensil tablets and those on placebos did not differ. Both  studies reported a falling off in hot flushes over a period of several months in both treatment and placebo groups.

     The researchers in both studies hypothesized that women in the placebo group may have increased isoflavones in their diet, and Novogen, who funded the trials, has promoted this as nullifying the disappointing results. However, as the trials were  blinded, there was no reason why women in the placebo groups alone would have increased their dietary isoflavones.

    The high placebo response is a phenomenon also reported in studies of conventional hormonal replacement therapy, and may  be the result of a natural lessening of hot flushes over time, or the benefit of being part of a trial where menopausal symptoms are discussed and taken seriously.

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A joint government-industry tribunal has upheld a complaint that successful Australian biotech company Novogen misrepresented scientific evidence in advertisements for its top-selling Promensil, which is aimed at women at menopause. 

 If you are taking hormones or blood-thinning drugs (such as Coumadin [warfarin], heparin, Trental [pentoxifylline], or even aspirin), red clover should be used only under a physician's supervision.