A researcher said on April 9 that so little is known about how plant estrogens act on the human body that sales of soy supplements as a natural alternative to hormone replacement therapy (HRT) must be questioned.

Soy is being widely promoted as a natural alternative to HRT. This is because it contains genistein, a plant estrogen that has similar but weaker effects to normal estrogen found in women.

But Dr. Saffron Whitehead, reader in reproductive physiology at St. George's Hospital Medical School, London, said new studies on human cells have shown that genistein and other phyto-estrogens may also stop the enzymes that make these hormones.

This could explain why the incidence of breast cancer, which in many cases is dependent on estrogen, is about two-thirds lower amongst Japanese and Chinese women who consume diets rich in soy compared with women living in England.

Whitehead's team examined the effects of phyto-estrogens on human ovarian cells obtained during procedures for in vitro fertilization.

The results showed that several phyto-estrogens, including genistein, inhibited the conversion of androgens to estrogens.

The researchers believe this could be significant in postmenopausal women because as these women's ovaries cease to function, their only source of estrogens is converting androgens released by their adrenal glands.

"This finding is potentially important to the phyto-estrogen story," Whitehead added in a statement. "We really don't know how phyto-estrogens act in the human body. They could be weak estrogen mimics, estrogen blockers or enzyme inhibitors.

"If they do stop the natural production of estrogens, we should consider whether soy supplements be sold as a natural alternative to HRT."

Annual Meeting British Endocrine Society's in Harrogate, Yorkshire England April 9, 2002

Dr. Mercola's Comments:

I am not opposed to all soy. Clearly Asian cultures show benefit from consuming soy products. The central issue that is missed though, is that most of the soy Asians consumed is fermented. Natto is a slimy foul smelling fermented soybean preparation that has been used in eastern Japan for over 1,000 years. Interestingly, natto has some of the highest content of vitamin K2 of any food known to man. Mostly Asian researchers have extensively studied Vitamin K2 and found it to be a profoundly useful tool to treat and reverse osteoporosis. Tempeh and miso are also other fermented soy products that are likely to have nutritional benefits. It would be unwise to assume that highly processed foods like tofu and soy protein would provide similar benefits as the fermented whole foods. From a vitamin K2 perspective, it is quite clear that the non-fermented soy foods, provide absolutely no vitamin K2 and will not protect and treat osteoporosis. If you are still confused about this issue, don't worry. This is a highly controversial area. If you have some free time and want to review some of the many hundreds of pages I have compiled on this subject, please review the soy index below. Related Articles: Soy Index