SupplySide

Seeking Soy Isoflavones

October 1, 2004 Lynn A. Kuntz Comments

Posted in Articles, Soy, Healthy Foods, Topics

Over the last decade or so, interest -- and the accompanying research into their health benefits -- in soy isoflavones has grown. They may play a key role in preventing certain cancers and also provide some of soy's protective effect to the cardiovascular and skeletal systems. Research also suggests they offer relief of menopausal symptoms, such as hot flashes, and might benefit cognitive ability. This has induced product designers to include them in functional foods, especially those targeting women's health.

Basic biochemisty

Soy isoflavones belong to a class of compounds called phytoestrogens, naturally occurring plant chemicals that mimic or interact with human estrogen. Soy contains three primary isoflavones, genistein (4' 5, 7-trihydroxyisoflavone), daidzein (4', 7-dihydroxyisoflavone), and glycetein (7, 4'-dihydroxy-6-methoxyisoflavone), as well as their ß-glycosides, genistin, daidzein and glycitin. The glycosides can have an attached acetyl or malonyl group. While some argue that the aglycone form has better bioavailability than the glycosidic, the debate is more academic than nutritionally important.

Soy isoflavones exhibit a weak estrogenic effect, about 1/100 to 1/1,000 that of estradiol, a human hormone. In some cases, they also show antiestrogenic activity. Research has ascribed their benefits to hormonal as well as nonhormonal properties.

Because estrogen lowers LDL cholesterol and increases the HDL form, many researchers believe isoflavones greatly influence the cholesterol-lowering effect of soy protein. Current studies point to a combination of soy protein and isoflavones for the maximum cholesterol-lowering effect.

"In 1999, the FDA authorized a health claim linking soy protein consumption to a reduced risk of heart disease," says Greg Paul, Ph.D., director, health & nutrition, The Solae Company, St. Louis. "Since then, health claims similar to this have been approved in other countries." However, product designers need to keep in mind that the FDA allows soy protein/cardiovascular claims regardless of isoflavone content.

"While soy's heart-health benefits are well-known, a good body of research shows moderate amounts of soy may be effective in reducing the risk of various types of cancer including breast, prostate and colon, and perhaps even uterine and endometrial," says Lisa Kelly, M.P.H., R.D., communications director, United Soybean Board, Washington, D.C.

Theoretically, soy phytoestrogens might help reduce cancer risk because they lower lifetime exposure to natural estrogens by competing for receptor sites or changing the way the body breaks them down. Researchers have identified isoflavones as the reason breast-cancer rates in Japanese and Chinese women are one-fifth that of their Western counterparts. Asian women consume approximately 20 to 80 mg of isoflavones daily versus less than 5 mg per day on average for U.S. women. Currently, a health-claim petition submitted by The Solae Company linking soy protein consumption and a reduction in the risk for certain cancers is under review by the FDA.

Bone health may be another area where isoflavones can provide an advantage. Research suggests that high intakes of isoflavones may increase bone mineral density in postmenopausal women and reduce their osteoporosis risk. "According to a recent study done with SoyLife, a dose of 80 mg isoflavones --expressed as aglycones -- helped postmenopausal women maintain bone mineral concentration at the hip," says Jocelyn Mathern, R.D., technical specialist, Acatris Inc., Minneapolis. "This is consistent with other research, which has shown beneficial doses of 80 to 90 mg isoflavones for bone health. While dosage of soy isoflavones is important to consider, other factors may influence their effect on bone health. For example, researchers found that the effect of SoyLife in protecting BMC was more marked among women that were later in menopause, in women with lower body weight or among women with a lower calcium intake."

While most studies show positive results, concerns have been raised that excess soy-isoflavone consumption might promote certain problems, such as: goiters in iodine-deficient diets; reproductive problems, such as infertility; and, in some cases, promotion of existing cancer cells. However, according to Kelly: "While myths about adverse health effects of soy, such as promoting goiters or infertility have circulated for many years, in reality there is little if any scientific evidence supporting these claims. A recent review of 18 different studies concludes that soy has no effect on breast-cancer risk, except possibly when consumed during adolescence or eaten in extremely high amounts. Women at high risk for breast cancer should discuss any diet changes or concerns with their health-care provider."

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