Author: Winston Craig, MPH, PhD, RD.
Oriental cuisine has become very popular in America. We have a surge of interest in food products derived from the soy bean, due to the health benefits they provide. Soy contains a variety of health-promoting phytochemicals that decrease the risk of a number of chronic diseases.
Using soy products four or more times a week markedly reduces the risk of breast and prostate cancer. Asian populations using tofu regularly have one-half the rate of cancer seen in similar communities not using soy products. A regular use of soy lowers the risk of cardiovascular disease. The isoflavones in soy decrease LDL cholesterol levels, and improve the elasticity of the arteries. Clinical trials with menopausal women reveals that a regular intake of soy protects against bone loss and hence reduces their risk of osteoporosis.
While some studies show a decrease in total and LDL cholesterol levels other studies fail to show any beneficial effect of soy isoflavones on lipid profiles. In most studies, beneficial effects could not be attributed with certainty to the isoflavones. If these components have any health-promoting effect in humans, it is small compared with the effect of soy protein itself.
Soy is well known to lower blood lipid levels, while the isoflavones isolated from the soy protein, and taken as a daily supplement, have no effect on blood lipids.
A Summary of the Health Benefits of Soybeans
- In postmenopausal women that had type 2 diabetes, daily supplementation with 30 grams of soy protein containing 132 mg of isoflavones (phytoestrogens) favorably altered their insulin resistance, blood glucose control, and serum lipids, and hence improved their cardiovascular risk profile. After 3 months of using the isoflavone-rich soy protein, the mean values for fasting insulin had dropped 8%, insulin resistance was 6.5% lower, and LDL cholesterol dropped 7%. No significant change occurred in HDL cholesterol or triglycerides.
- Premenopausal Japanese women having the highest soy intake had a spinal bone mineral density (BMD) that was 8 percent higher and a hip BMD that was 12 percent higher than the Japanese women with the lowest soy intake.
- A new study suggests that a high soy intake during adolescence reduces the risk of breast cancer in later life by about 50 percent.
- High consumption of soy products is associated with an increased lumbar spinal bone mineral density in postmenopausal Japanese women.
- The calcium added to soy beverages is absorbed 25% less efficiently than the calcium in cow milk.
- Soy protein, rich in naturally occurring isoflavones, was observed to attenuate spinal bone loss of peri-menopausal women over a six month period.
- Studies on soy, rich in isoflavones, continues to show its effectiveness in reducing the risk of breast and prostate cancers, osteoporosis, and heart disease. Recently, when researchers from Wake Forest University fed soy protein to 156 subjects for 2 months they observed significant drops in blood lipids, especially in those with initially elevated cholesterol levels. In such persons blood cholesterol and LDL cholesterol levels fell 9 and 10 percent, respectively. Low-fat choices may not provide these beneficial effects since low-fat soy milk and low-fat tofu are low in the health-promoting isoflavones. Furthermore, the use of antibiotics has a negative effect on isoflavone metabolism, so that a regular use of antibiotics may negate the positive effect of soy in the diet.