Does Soy Have a DARK SIDE?

Natural Health, March, 1999 by Sally Eauclaire Osborne

Does Soy Prevent the Absorption of Minerals?

The bran or hulls of seeds, found in beans, grains, nuts, and other plant foods, contain phytates (or phytic acids). These phytates bind to essential minerals such as calcium, iron, and zinc in the digestive tract and prevent them from being absorbed.

Soybeans possess a lot of phytates; some researchers say more than other beans. Additionally, soy's phytates are so strong that many survive phytate-reducing techniques such as cooking. (The phytates in whole grains can be deactivated by some soaking or fermenting techniques.)

Fallon and Enig say only long periods of soaking and fermenting--as are used in making miso, natto, shoyu, tamari, and tempeh (but not tofu, soymilk, texturized soy protein, or soy protein isolate)--significantly reduce the phytate content of soybeans. Anderson and Wolf, in their article in the Journal of Nutrition in 1995, also report that tempeh has lower phytate levels than unfermented soyfoods. Fallon believes that eating more than 12 g of these unfermented foods a day (equal to about a tablespoon) can lead to a shortage of crucial minerals.

But not everyone agrees that phytates are a bad thing. They can move excess minerals out of the body. Stephen Holt, M.D., a gastroenterologist and author of The Soy Revolution: The Food of the Next Millennium (M. Evans and Company, 1998), says phytates shield us from dangerously high levels of minerals such as iron. And some animal studies have suggested that phytates stop the growth of cancerous tumors. In Earl Mindell's Soy Miracle, Mindell writes that phytates can bind with minerals that may feed tumors.

Does Soy Cause Hormone Havoc?

The plant estrogens (phytoestrogens) found in soy, including isoflavones, resemble the natural estrogens in our body. This could be why soy consumption promises relief from menopausal symptoms, among other benefits. Yet critics of soy say these isoflavones could cause two specific problems.

First, some researchers speculate that an isoflavone-rich diet could interfere with our ability to reproduce. Scientists have linked infertility to the soy diet of animals such as cheetah and quail. For example, researchers at the Children's Hospital Medical Center in Cincinnati, Ohio, analyzed the diet of cheetahs living in zoos to figure out why the animals experienced infertility. In the journal Gastroenterology in 1987, the researchers theorized that the cheetahs' phytoestrogenrich soy diet was probably a major factor.

Messina says it's possible but unlikely that soy could affect fertility, "but as far as I know there's no problem with reproduction and fertility in the Japanese population or in the American vegetarian population [two groups that eat soy]."

(According to Soyatech, Inc., a soy research firm in Bar Harbor, Maine, the estimated daily soybean consumption was 9 g per capita in China and 30 g per capita in Japan in 1991. In the United States, the estimated daily consumption was 7.5 g per capita in 1991; it rose to 11.2 g in 1996. One cup of cooked soybeans equals 180 g.)