Author: Winston Craig, MPH, PhD, RD.
Soybeans have been used for everything from soap to ink. The Chinese believe that soy can cure a number of diseases and medical conditions. In the word for soybean is ta-tou, which means “greater bean”. While soybeans have been widely used throughout Asia for centuries (the average Japanese eats over 50 lbs of tofu a year), it is only in the past few decades that Americans have begun to accept soy into their diet. Today, soy is found in many foods available in the supermarket, such as tofu, soy beverages, soy cheese, soy sauce, tempeh, soy-based meat substitutes, infant formulas, soy nuts, tofutti and ice-bean.
It has been known for some time that soy protein is a high quality protein equivalent to the protein quality of egg, milk or meat. Now, scientists are taking a very careful look at the health promoting properties of this mighty little bean. Research shows that soy may be useful for lowering the risk of heart disease, cancer, kidney disease, osteoporosis and other problems.
The mechanism for the action of soy is not known, at this time. The isoflavones in soy are known to be potent inhibitors of cholesterol synthesis in the body. Also, the phytosterols and saponins in soy can block cholesterol absorption from the diet or increase cholesterol excretion from the body, thus lowering blood levels. In addition, soy can prevent the oxidation of LDL cholesterol and also inhibit clot formation, thereby lowering the risk of cardiovascular disease.
Consumption of soybeans is suggested as a contributing factor in the low incidence of breast and prostate cancer in Japanese women and men, respectively. Dr Barnes has shown that the isoflavones (genestein and daidzein) in soy inhibit the growth of both human breast cancer and prostate cancer. Studies at Cambridge on young women revealed that those who daily consumed soy protein for a month had their menstrual cycles lengthened 2-3 days, due to the lengthening of the follicular phase. During the luteal phase of the cycle, hormone levels are normally high. This stimulates breast cell proliferation. A diet that lengthens the follicular phase may mean less luteal phases over a lifetime. This may translate into a reduced risk of breast cancer. In another study, Japanese women who consumed 2 ozs/day of soybeans or soy products (e.g. tofu, miso) reported fewer hot flashes and other symptoms of menopause than women in the USA not eating soy.
It has been known for years that diets containing meat can result in a greater excretion of calcium than similar diets containing soy. This is important for individuals concerned about osteoporosis since calcium excretion affects calcium balance more than what calcium absorption does. Scientists have now found that components of soy can actually inhibit bone resorption, thereby reducing the risk of osteoporosis.