By Eric Rosenberg

After the U.S. Food and Drug Administration allowed food manufacturers two years ago to claim that soy-based foods help lower the risk of heart disease, a bumper crop has appeared on grocers' shelves.

Consumers can find soy hot-dogs, soy garden burgers, soy cheese, milk and butter, breads made from soy flour, soy power bars, soy ``meats'' and raviolis - not to mention the old standbys of tofu, miso and soy sauce.

The growth in soybean usage in the last decade has outpaced every other food commodity, including rice, corn, cotton and wheat.

US farmers are expected to plant a record 76.7 million acres of soybeans this year, up 3 percent from last year's record planting, according to the US Department of Agriculture.

But conflicting opinions are now emerging among researchers about soy's health benefits.

Where soy was once universally regarded as a wonder food - capable of stemming disease, warding off cancer and providing inexpensive nutrition to boot - now there is some concern that soy may be a source of estrogen and, as such, could promote breast cancer in some women.

Soy has this healthy cache. Everybody thinks that soy can't be anything other than good,'' she said. Initially, the soy enthusiasts made it sound like the scientific evidence was very sound.

But we need more to determine whether it is safe.

Like all foods, soybeans are comprised of complex chemical components. The main components are protein, essential fatty acids and to a lesser degree what are known as isoflavones.

This family of chemicals is also found in other legumes. The versions in soybeans - genistein, daidzein, glycitein and equol - are also phytoestrogens - plant-derived weak estrogens, chemically similar to the female hormone estrogen.

As a result, some physicians caution breast cancer patients against eating too much soy for fear it could promote tumor growth in women whose disease is sensitive to estrogen.

In addition, health agencies of New Zealand, Australia and Great Britain have voiced concern about the safety of soy-based infant formula for fear that it might spark reproductive or thyroid problems in babies in later life.

Wahida Karmally, spokeswoman for the American Dietetic Association, which represents US nutritionists, says the advice to women who have breast cancer is to use soy in moderation. "We don't know if it's dangerous, but we should be conservative about it until we do know,'' she added.

Much of the current debate over soy safety began two years ago when two FDA scientists raised red flags at a time when the agency was considering whether to allow the health claim by food manufacturers.

Daniel Sheehan and Daniel Doerge, both senior toxicologists at the FDA, strongly opposed the soy health claim and wrote a memorandum outlining their concerns.

``We oppose this health claim because there is abundant evidence that some of the isoflavones found in soy demonstrate toxicity in estrogen sensitive tissues and in the thyroid,'' they said.

``Given that a women's own estrogens are a very significant risk factor for breast cancer, it is unreasonable to approve the health claim until complete safety studies of soy protein are conducted,'' they wrote, citing 28 studies suggesting the possible toxic effects of soy.

Because the FDA regulates drugs that contain estrogen, soy products should have warning labels advising consumers about the chemical contents, according to Sheehan and Doerge. ``The public will be put at potential risk from soy isoflavones in soy protein isolate without adequate warning and information,'' they wrote.

Although the FDA leadership ultimately overruled the two scientists, officials acknowledge the concerns should be taken seriously.

Regina Ziegler, an epidemiologist with the US National Cancer Institute and a soy researcher, said that more studies are under way into soy safety, including one by the National Institutes of Health on infant formula.

But, she cautioned, ``there's not the perfect study out there It's not like there's just one study that needs to be done and then we'd get the answer.''

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