Soy may be effective for reducing hot flashes or at least reducing their potency. This article examines soy and other soybean products and why they may help.

Soy and phytoestrogens: genistein and daidzein

Phytoestrogens are derived from plants. Various classes of phytoestrogens exist, including isoflavones. The two isovlavones found to have significant estrogenic responses in vitro are genistein and daidzein. Soybeans are a major source of isoflavones. Soy products are a major source of phytoestrogens, including soybeans, tofu, tempeh, soy flour, soy milk, and soy cheese. Soy meat and soy sauce also contain some phytoestrogens, but in less quantities. The less processed the soybeans, the more isoflavones they contain. Cooked soybeans and tempeh are probably the least processed, followed by soy flour, tofu, soy milk, soy cheese and soy meats.

There is confusion about the workings of phytoestrogens. The phytoestrogens in soy are of a much reduced potency than estrogen, in fact, they contain anti-estrogenic potency. Isoflavones (such as appear in soybeans and other soy products) also protect against breast cancer. Although conventional hormone replacement therapies increase mammographic breast density, the isoflavones do not.

The evidence for soy reducing hot flashes

Nineteen trials involving more than 1,700 women show that soyfoods or isoflavone supplements can alleviate hot flashes or hot flushes and reduce their frequency.

Sources:

Atkinson C, Warren RM, Sala E, Dowsett M, Dunning AM, Healey CS, Runswick S, Day NE, BIngham SA. Red clover-derived isoflavones and mammographic breast density: a double-blind, randomized, placebo-controlled trial. Breast Cancer Research, 2004, volume 6, number 3, pp. 170-9.

Messina M, Hughes C. Efficacy of soyfoods and soybean isoflavone supplments for alleviating menopausal symptoms is positively related to initial hot flush frequency. Journal of Medicinal Foods, 2003, Spring, pp. 1-11.

Mueller SO, Simon S, Chae K, Metzler M, Korach KS. Phytoestrogens and their human metabolites show distinct agonistic and antagonistic properties on estrogen receptor (ER) {alpha} and ER {beta} in human cells. Toxicological Sciences, 2004, April 14. (E published ahead of print)