General Description
The soybean (also called soja or soya bean) is an annual legume
cultivated in many types of soil. A branching plant ranging in height
from several centimeters to over 2 meters, the soybean has broad,
heart-shaped leaves and white or pale-purple blossoms. At maturity,
the plant bears irregular, oblong pods containing one to four seeds
a piece. The seeds (soybeans), which may be yellow, green, brown,
black, or bicolored, are a staple in the diet of people and animals
in many parts of the world. Soybeans were introduced into the United
States in 1804, and became a major agricultural comodity by the
mid-20th century. By the 1980s, the U.S. became the world's leading
soybean producer, followed by Brazil and China. Ninety-eight percent
of the U.S. crop is used for livestock feed.1
Health Applications
- Cardiovascular health
- Cancer prevention
- Osteoporosis
- Menopause
History and Traditional Use
Although the origins of the modern soybean plant remain obscure,
many botanists believe it is a derivative of Glycine ussuriensis,
a legume native to central China.1 For more
than 5,000 years, the Chinese have used soy as a food and for
medicinal purposes. Over the years, soy has proven to be a remarkably
versatile food, and it is now consumed in a variety of forms including
soy milk, tofu, tempeh, miso, soy flour, concentrated soy protein,
and soy sauce. Soybean oil can be processed to make food products
such as shortening, margarine, and vegetarian cheese, and industrial
products such as ink, paints, fertilizers, and adhesives.
Chemical Composition
Commonly used as a meat substitute because of their high protein
content, soybeans are also rich in lecithin, potassium, phosphorus,
magnesium, and iron; and contain significant amounts of thiamin,
riboflavin, niacin, and vitamin C. In addition to these basic
nutrients, soybeans contain compounds called isoflavones, which
have been shown to have unique biological activity. The two best-known
soy isoflavones, genestein and daidzein, are often referred to
as "phytoestrogens" because of their estrogen-like activity in
the body.
Cardiovascular Health
Among the most studied properties of soy has been its role in
cholesterol reduction and cardiovascular health. In 1999, after
a review of the scientific evidence, the Food and Drug Administration
concluded that soy protein, as part of a diet low in cholesterol
and saturated fat, may reduce the risk of coronary heart disease
(CHD) by lowering blood cholesterol levels.2
Studies indicate that the cardioprotective properties of soy protein
may be due largely to its isoflavone content. Isoflavones have
been shown not only to lower LDL ("bad cholesterol") and raise
HDL ("good cholesterol") concentrations, but also to protect LDL
from oxidation.3-5 All of these effects are
viewed as protective against atherosclerosis and CHD.
Menopause
The estrogen-like activity of soy isoflavones may be of value
in the treatment of menopaual symptoms. In several studies, soy
isoflavones have been shown to be effective in reducing the frequency
and severity of hot flashes.6-9 Other studies
indicate that soy may have a protective effect against post-menopausal
bone loss (osteoporosis).10-13 The cardioprotective
effects of soy may be particularly valuable for post-menopausal
women, as the risk for heart disease increases after menopause.
Cancer Prevention
A number of studies suggest soy isoflavones may have a protective
effect against certain types of cancer. Studies on laboratory
animals and in vitro studies using human cells indicate that genestein
inhibits cancer cell growth and may induce apoptosis (programmed
cell death) in prostate cancers.14-17 In one
small-scale study, frequent consumption of soy milk was associated
with a 70 percent reduction in prostate cancer risk.18
Preliminary studies suggest that soy isoflavones may have a protective
effect against breast cancer as well.19-23
However, large-scale human-based trials are needed before the
potential for soy in cancer prevention can be determined.
Dosage/Toxicity
Soy is consumed widely as a food and has not been associated with
any toxicity. Daily soy intake providing the equivalent of 25
grams soy protein or more are recommended for lowering cholesterol
levels.2 |
