In the early 1990's, there was an explosion of Western interest in the traditional asian food, soy. This perfect protein-packed bean appeared to prevent breast cancer, increase bone mass, relieve hot flashes, lower cholesterol, and help prevent heart disease. As a food, soy offers a "complete" protein profile. Soybeans contain all the amino acids essential to human nutrition, which must be supplied in the diet because they cannot be synthesized by the human body. Soy protein products can replace animal-based foods--which also have complete proteins but tend to contain more fat, especially saturated fat--without requiring major adjustments elsewhere in the diet.
In the past 15 years the American health food industry has added soy to every food imaginable and grocery store shelves are now lined with an ever-growing supply of soy products. Its available in its traditional Asian forms — as tofu, tempeh or edamame — while soy protein powder and isoflavone-packed supplements abound. Soy is ground into burgers and hot dogs, processed into cheese, milk and ice cream, and added to cereals and energy bars. Soy baby formula is now fed to an estimated 10% to 20% of U.S. infants. Sales of soy products are up and expected to increase even more.(1)
Millions of dollars have been poured into research, and now concerns about soy's health benefits and safety are surfacing. Researchers are discovering that some of the claims made for soy were based on preliminary evidence and a number of more recent, well-done studies have tempered the original findings.
The American Heart Association Committee has released a statement that soy protein itself has little direct effect on cholesterol. However, soy foods are good for the heart and blood vessels because they usually replace less healthful choices, like red meat, and because they consist of polyunsaturated fat, fiber, vitamins, and minerals, and are low in saturated fat.(2)
With respect to breast cancer, studies so far haven't provided a clear answer. Some studies show a benefit while others have found no association, and yet a small number of studies have found that concentrated supplements of soy proteins may actually stimulate the growth of breast cancer cells.(5) Large prospective studies are now in progress and should offer better information regarding soy and breast cancer risk.
The specific concerns about soy focus on components of soy, such as the soy isoflavones daidzein and genistein, not the whole food or intact soy protein, such as tofu. These chemicals, available in over-the-counter pills and powders, are often advertised as dietary supplements for use by women to help lessen menopausal symptoms such as hot flashes. Unlike soy foods, supplements contain high levels of estrogen-like isoflavones, such as one called genistein. Estrogens can promote the growth of certain breast tumors. Recent, carefully controlled studies have not found soy significantly helpful in relieving hot flashes(4) and The American Heart Association does not recommend isoflavone supplements (pills or powder).(2) Not only are there safety concerns, but these supplements are not effective in relieving hot flashes.