SOY IS A MANY-SPLENDORED THING
In an era when vegetables are celebrated increasingly for their disease-preventing potential, the soybean is beginning to emerge as one of the best and brightest of the crop. If weíre to believe what we read, soy is a many-splendored thing. Its protein is complete, its fiber is plentiful, its oil is non-atherogenic. Moreover, itís filled with phyto(plant)estrogens called isoflavones, which may confer many of the benefits, but fewer of the risks, of the synthetic or animal-derived hormones.
The following is a summary of soyís effects:
Reduced risk factors for heart disease. In controlled clinical trials, soy consumption has repeatedly reduced total cholesterol, LDL (bad) cholesterol, and triglycerides without lowering levels of HDL (good) cholesterol. In many of theses studies, the reductions were substantial. An analysis of 38 studies involving a total of 730 volunteers indicated an average reduction of 23.3 mg/dl in total cholesterol, of 21.7 mg/dl in LDL-cholesterol, and of 13.3 mg/dl in triglycerides. In most of the trials, soy protein was exchanged for animal protein without adding or subtracting calories.
In a recent study at the University of Illinois, 66 postmenopausal women, all of whom had total cholesterol levels above 200 mg/dl, spent 6 months on a low-fat diet in which protein was furnished either by skim milk or soy products. Although all had significant reductions in total cholesterol, only the women on the soy diet had a significant reduction in LDL cholesterol as well as a significant increase in HDL cholesterol. Soy may well have other beneficial effects on blood vessels. In laboratory experiments the principal soy phytoestrogen, genistein, has halted growth in several cell types. Some researchers have speculated that it may work in a similar fashion to prevent an early stage of atherosclerotic plaque the overgrowth of the epithelial cells lining the arteries. There is some evidence that it may, like estrogen, increase the flexibility of blood vessels, helping to prevent spasms that can trigger heart attacks.
Reduced risk for breast cancer. Spurred by the observation that Asian women, who pursue a soy-rich diet, have a significantly lower rate of breast cancer than American and European women, researchers have looked for compounds that might have a preventive effect. They have homed in on genistein, which functions somewhat like tamoxifen and other antiestrogens it shares a few, but not all, of estrogenís properties. Specifically, genistein seems to be close enough to estrogen to allow it to stick to estrogen receptors on a breast-cancer cell, but not close enough to get inside the cell. Thus, it sits there, blocking estrogenís passage into the cells and thus denying tumor cells a powerful growth factor.
Whether this effect holds true in women remains to be seen. There are a number of trials in progress to determine whether diets containing soy or genistein prevent breast cancer. However, it will be several years before the results are known.
Reduced risk for osteoporosis. Researchers at the University of Illinois also took bone density measurements of the postmenopausal women enrolled in the cholesterol study mentioned above. They found that those on the soy diet had a significant increase in bone density, which was limited to the spine, during the 6 months of the study.
Again, genistein appears to be responsible. However it doesnít seem to mimic estrogen in its approach to bone-building. In animal studies, genistein spurs bone formation, while estrogen slows bone resorption the process that results in the breakdown and redistribution of bone minerals.
Relief of menopausal symptoms. Results from a controlled 6-week study of 51 perimenopausal women at Bowman Gray School of Medicine are promising. The women reported fewer hot flashes and night sweats during the weeks they drank an 8-ounce soy beverage daily than they did during an equal period in which they consumed a carbohydrate drink that was identical in appearance, taste, and caloric content.
This line of research is expanding. The Bowman Gray researchers are continuing to study the soy beverage in a larger, longer study, and researchers at Tufts University School of Medicine are testing the effects of soy-based breakfast bars in relieving perimenopausal symptoms.
It goes without saying that the data on the benefits of soy are preliminary at best. No one has tested soy against other measures to lower cholesterol or preserve bone. No one knows the extent of its effects when used in conjunction with estrogen supplements, either in HRT or in oral contraceptives.
Moreover, the isoflavone content of soy varies among varieties of the bean, and is dependent upon the methods used to process prepared foods. The manufacturer may list isoflavone content on the package, but isnít obligated to. However, as a rule, soy sauce and soy oils are low in isoflavones, while roasted soy nuts, tempeh, and tofu are high, affording about 40 mg per 1/2 cup. Soy milk has 40 mg per cup.
If you plan to incorporate more soy products into your diet, go slowly dramatically increasing soy intake can cause gas. It may be wise to stay within the 30 50 mgs of isoflavones that are consumed by the average Japanese woman daily, because the effects of eating greater quantities are unknown. And donít overlook the fat content, which can account for up to half the calories, in some soy products or the sodium content, which is often high.
Written by: The United Soybean Board
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