Genistein is a naturally occurring chemical present in soy. It is a type of chemical called a phytoestrogen, an estrogen-like substance present in some plants. Soy is a staple food in many Asian countries. It contains valuable constituents, including protein, isoflavones, saponins, and phytosterols. Soy protein provides essential amino acids and can be used as effectively as animal protein by adults. It’s also low in fat and cholesterol-free. The isoflavones in soy have antioxidant and phytoestrogenic properties and saponins enhance immune function.

High cholesterol.  Menopause. Osteoporosis. Vaginitis*.

Heart disease.  Atherosclerosis. Osteoporosis.  Hormone-dependent cancers, such as breast and prostate cancer.

The optimum dosage of genistein is unknown. Researchers suggest that the equivalent of one serving of soy foods per day supports good health, and the benefits increase as soy intake increases. Societies that eat a high intake of soy products derive between 50 and 100 mg per day of soy isoflavones. The FDA suggests a daily intake of 25 g of soy protein to reduce cholesterol. Studies have used dosages of up to 40 g daily.

Genistein is found in high quantities in soy and in negligible quantities in a few other foods. Most soy foods contain about 1 to 2 mg of genistein per gram of soy protein. In addition to whole soybeans, foods derived from soy include tofu, tempeh, soymilk, textured and hydrolyzed vegetable protein, meat substitutes, soy flour, miso, and soy sauce. Soy is also available as a supplement, as soy protein or isoflavone in powder, capsule, or tablet form.

Studies in animals have found genistein essentially nontoxic. Certain constituents in soy interfere with or alternatively might increase thyroid function; however, the clinical importance of this problem remains unclear. Side effects other than those listed here may also occur. Talk to your doctor about any side effect that seems unusual or which is especially bothersome.

Acute Overdose: None Chronic Overdose: None

Soy products and cooked soybeans are safe at a wide range of intakes. However, a small percentage of people has allergies to soybeans and thus should avoid soy products.  Soy contains a compound called phytic acid, which can interfere with mineral absorption. Certain medications interact in a positive and/or negative way with soy. Because of its effects on estrogen, there are at least theoretical concerns that genistein may not be safe for women who have already had breast cancer.  Some experts fear that soy isoflavones might interfere with the action of oral contraceptives, however one study suggests that such concerns are groundless. Pregnant or nursing women should talk with a doctor before taking genistein or huge amounts of soy. Individuals with impaired thyroid function should use soy with caution.