Soy: The Perfect Diet Food For Us?

For years, soy has been touted as a near-miracle food. Soybeans contain a large amount of protein and nutrients and no cholesterol. Proponents claim that a diet rich in soy protein can help prevent heart disease, while the isoflavones contained in soy may help prevent some forms of cancer.

However, some researchers are beginning to question whether soy really produces so many health benefits. The U.S. Food and Drug Administration is reviewing its 1999 ruling that a diet including soy protein can reduce the risk of coronary heart disease, after that claim came under question by the American Heart Association and other health groups. Also, recent research has undermined claims that soy isoflavones can prevent prostate or breast cancer.

Soy: What Are the Benefits?

Soybeans are an undeniably healthy food for your diet, says Christine Gerbstadt, MD, spokesperson for the American Dietetic Association. "Soy has a lot of healthy fats, high fiber, and high protein. There are a lot of good reasons for including one or two servings every day."

Foods derived from soybeans, like tofu or soy milk, are good substitutes for animal products that contain cholesterol. Soy also is rich in healthy nutrients like B vitamins and omega-3 fatty acids.

Proponents also claim a number of health benefits, saying soy products can help prevent:

• Coronary heart disease. The FDA said in 1999 that eating at least 25 grams of soy protein in your daily diet can lower your total cholesterol as well as your levels of "bad" LDL cholesterol.
• Cancer. Soy contains large amounts of phytoestrogens, plant-based chemicals that act like a weak form of the female hormone estrogen. The most potent phytoestrogens in soy are called isoflavones. Some research has indicated that these phytoestrogens might help reduce a person's risk of breast or prostate cancer.
• Menopause symptoms. Research also has found that soy-based phytoestrogens might alleviate some menopausal symptoms, including hot flashes and osteoporosis.

Soy: Drawbacks and Questions

Despite its positive nutrients, soy isn’t tolerated by everyone. Many people, particularly children and infants, can become allergic to soy. When that happens, they will need to avoid soy completely in their diet or experience an allergic reaction.

In terms of those health claims, some are now being disputed, or at least questioned. Doctors are asking whether the phytoestrogens contained in soy might actually promote breast cancer, Dr. Gerbstadt says. "For some women with increased risk factors for breast cancer, they might want to watch how much soy they eat," she says. "It can promote the hormone balance that would be more likely to promote cancer in some women."

There's also an ongoing and increasingly contentious medical debate over the heart health claims that have been made about soy. The FDA is reviewing its 1999 ruling that found a diet including soy protein effective in lowering cholesterol. The American Heart Association (AHA) asked for this review, saying the heart health claims may not be supported by strong evidence.

In its letter, the AHA said most of the research showed that soy protein in large amounts could lower LDL cholesterol a few percentage points when it takes the place of meat or dairy proteins, but only with large amounts of soy. Furthermore, the letter said, the research was done on people whose cholesterol levels were very high. Also, the research didn’t show any benefits to blood pressure or HDL, the “good” cholesterol. Therefore, it concluded, any direct benefit to the heart was minimal.

Researchers are also questioning claims related to soy's ability to prevent cancer. For example, a recently released Canadian study found no evidence that soy could help prevent prostate cancer in men with precancerous prostate lesions.

The bottom line: Soy is a great source for certain important nutrients, especially if you avoid meat and dairy. But consider it just one food of the dozens that make up a balanced diet.