Soy capsules’ effects are not clear

Although soybeans are a top agricultural product in the United States, soy products remain more popular abroad -- particularly in Asia -- than here at home. Many studies have linked soy-rich diets with good heart health, but the effects of soy supplements are less clear. Most are formulated to provide high concentrations of isoflavones -- plant chemicals such as genistein and daidzein that are found in soybeans and behave similarly to human estrogen.

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Uses: Soy isoflavones are promoted for fighting cancer and heart disease, preventing osteoporosis, treating kidney disease and, most commonly, managing menopausal symptoms .

Dose: Usually 80 to 200 milligrams three times a day, in capsules taken with food. Soy protein powders may not contain the same concentration of isoflavones as pills.

Precautions: Soy foods are safe, but the safety of concentrated isoflavones has not been well studied. Soy supplements should be avoided by people allergic to soy and women with breast cancer, since some lab studies show that isoflavones may encourage breast tumor growth.

Research: Animal and lab studies suggest isoflavones may help prevent osteoporosis and cancer, but results are inconsistent and human research is still needed. Several studies are looking at the effects of isoflavones on menopausal symptoms.

Dietary supplement makers are not required by the U.S. government to demonstrate that their products are safe or effective. Ask your health-care provider for advice on selecting a brand.

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-- Elena Conis