Greater amounts of isoflavonoids (a phytoestrogen) in the urine may be more common among women who regularly exercise and may be linked to higher soy intake, according to a study.

The word "phytoestrogen" is derived from phyto, meaning "plant" and estrogen, because of the ability of these compounds to affect estrogenic activity in the body. Phytoestrogens are a diverse group of polyphenolic, nonsteroidal plant compounds that may cause both estrogenic and antiestrogenic effects. The estrogenic effects of phytoestrogens are similar, although less intense, than those of estrogens made by the human body.

Soy contains protein, isoflavones and fiber, all thought to provide health benefits. Soy is an excellent source of dietary protein, including all essential amino acids. Soy is also a source of lecithin or phospholipid. Soy isoflavones and lecithin have been studied scientifically for numerous health conditions. Isoflavones such as genistein are believed to have estrogen-like effects in the body, and as a result are sometimes called phytoestrogens.

In a new study, researchers evaluated 2,165 women between the ages of 40 and 70 who participated in the Shanghai Women's Health Study. The team measured the amount of phytoestrogens released in the urine and compared this to lifestyle and dietary factors.

They found that women who exercised regularly tended to have the highest urinary phytoestrogen excretion. Higher excretion was significantly linked to soy intake, but was inversely related to fruit consumption.

The investigators concluded that their findings may help improve understanding on the potential health benefits of phytoestrogens in middle-aged and elderly women. However, more studies are needed.

Common sources of soy isoflavones include roasted soybean, green soybean, soy flour, tempeh, tofu, tofu yogurt, soy hot dogs, miso, soy butter, soy nut butter, soy ice cream, soy milk, soy yogurt, tofu pupsŪ, soy cheese, bean curd, seitan and soy noodles.