Soy and soy isoflavones
All varieties of soy foods, including soy beverage, soy meatless patties, soy flour, tofu, textured soy protein, soy nuts, and tempeh are derived from soybeans. Soy foods are becoming much more common in the American diet because studies have shown that certain components of the soybean, including soy isoflavones, soy protein, saponins and phytosterols provide many health benefits. Soy research is a very hot topic these days because scientists are still unsure of the exact mechanism by which soy benefits the heart. However, the American Heart Association says that enough evidence exists to recommend the consumption of 25 grams of soy protein per day to decrease the risk for heart disease.
Another great benefit of consuming soy is that it is a great source of protein, comparable to that found in animal products such as eggs and milk. Soy products are also low in saturated fat and have no cholesterol, which is another benefit for the heart.
Claimed Health Benefits
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Helps lower LDL (bad) cholesterol and triglyceride levels
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Decreases risk of developing heart disease
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Helps prevent osteoporosis
Food Sources
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Soy beverage
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Soy meatless patties
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Soy flour
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Tofu
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Textured soy protein
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Soy nuts
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Tempeh
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Yogurt with soy protein
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Soy butter (like peanut butter except made with soy beans)
Dosage
The American Heart Association recommends consuming 25 grams of soy protein per day to decrease the risk for heart disease. Research suggests consuming no more than 200 mg of soy isoflavones per day due to a lack of long-term effects. (a 1-ounce serving of tofu contains approximately 40-100 mg of isoflavones, and an 8-ounce glass of soy beverage contains approximately 100-150 mg of isoflavones)
Evidence for Health Benefits
Soy isoflavones are found in soy beans that are known to be good for the heart. Various studies, including one done at Iowa State University, have shown that soy isoflavones alone may not possess cholesterol-lowering effects. Instead, isoflavones may protect the interior lining of blood vessels by preventing them from becoming inflexible. This is what doctors call hardening of the arteries, or atherosclerosis, which could result in high blood pressure, heart attack, or stroke.
Studies have also shown isoflavones to have an estrogen-like effect in the body. Unlike the natural estrogen hormone produced in the body which can promote cancer growth, isoflavones can block this cancer-promoting action of estrogen by binding to estrogen receptors. Therefore, consumption of soy protein has been associated with a decrease in the incidence of cancer, particularly the incidence of breast cancer.
Other research has shown that soy may reduce the risk of osteoporosis as well. However, claims that soy isoflavones could alleviate menopausal symptoms are turning up negative.
Several studies show that soy protein can help lower LDL cholesterol (bad cholesterol) while maintaining the HDL cholesterol (good cholesterol) levels. Yet the exact mechanism of how this works is still under investigation.
Soy protein has also been associated with increasing bone density. Soy beans contain high amounts of calcium, and the protein in soy is associated with less calcium loss from the body than other sources of protein.
Cautions
Consuming soy products does not seem to be associated with any serious adverse health effects.
A high consumption of soy protein could result in stomach and intestinal discomfort, as seen with any diet high in protein.
Daily isoflavone intake seems to be safe up to at least 200 mg (the daily amount found in the average Japanese diet). Long term effects have not been reported for isoflavone consumption, so doses should be limited to 200 mg per day as amounts above this could result in adverse estrogen-like effects.
References
1. Iowa State University (2004) University Extension. http://www.extension.iastate.edu/newsrel/2003/aug03/aug0319.html Accessed January 6, 2004.
SupplementWatch, Inc. (2004)
2. Supplement Decisions Made Easy. http://www.supplementwatch.com/supatoz/supplement.asp?supplementId=267 Accessed February 5, 2004.