From The August 2000 Issue of Nutrition Science News

Any Soy Has Isoflavones

Soy food products contain the isoflavones daidzein and genistein, which are believed to help prevent osteoporosis and breast and prostate cancers. However, fermentation and processing can alter the form in which isoflavones are found, raising the question of whether certain foods are more protective than others. For example, almost all the isoflavones in cooked soybeans, textured vegetable protein and soymilk are found as glucosides, linked to a sugar molecule. In contrast, 20 percent of the isoflavones in tofu and 40 percent in tempeh are without linkages to other compounds. And since it was believed the body cannot manufacture the digestive enzymes that cut the link between isoflavones and sugars, a study was performed to determine if the body can effectively absorb isoflavones that are bound to other compounds.

To find out, eight women aged 20 to 41 were studied by Xia Xu and Suzanne Hendrich, Ph.D., of Iowa State University in Ames. Isoflavone metabolites in the urine were analyzed to determine absorption from different types of soy products consumed via different diets. The researchers found that the type of foods eaten with the soy product and the type of soy food consumed did not significantly affect the percentage of isoflavones absorbed. Furthermore, it was determined that bacteria in the gut do indeed break the link that connects isoflavones to other molecules, freeing the individual isoflavones for easier absorption.

—Journal of Nutrition 2000;130:798-801.