What are soy isoflavones?
Isoflavones are types of phytoestrogens (plant estrogens) found in
soy foods. Isoflavones have chemical structures similar to estrogen.
However, soy isoflavones have been found to have weaker effects on
the body than most estrogens and are not stored in the body. There
are two main isoflavones in soybeans and soybean products known
as daidzein and genistein.
What soy foods contain isoflavones?
tofu, soy beverages and tempeh all contain about 30 to 40 milligrams
of isoflavones per serving. One half cup of soy flour contains about
50 milligrams of isoflavones. Texturized soy protein and soy protein
isolates are also rich sources of isoflavones. Soy protein concentrates,
a widely used ingredient in soy products, usually does not contain
significant amounts of isoflavones. Soy hot dogs, soy-based ice cream
and other processed soy products have much lower amounts of isoflavones
because they frequently contain high amounts of non-soy ingredients.
Soy sauce and soybean oil do not contain isoflavones. For consumer
friendly information about soy foods, click on: http://www.soyfoods.com
The USDA's Agricultural Research Service has compiled a more complete
database of the isoflavones in soy foods.
What other nutrients besides isoflavones do soy foods provide?
Soy foods contain an abundance of other nutrients including protein
and minerals. Some soy foods are excellent sources of calcium. For
more information about the calcium content of selected soy beverages,
click on: http://www.soyfoods.com/nutrition/CalciumChart.html
How do soy isoflavones affect bone health?
The current understanding of the role of soy isoflavones in bone health
is in its infancy. The potential role of isoflavones in bone health
is not clear. Animal studies show some benefit of soy isoflavones to
bone health but the human studies do not consistently show a benefit.
Some studies have shown small increases in bone mass with isoflavone
intake while other studies have shown no apparent benefit.
If we compare bone mass between Americans and Asians with higher dietary
soy intakes, the bone mass is higher in Asians. However, there are
many other differences between these populations that could impact
bone mass. It is not known whether individuals who start to consume
soy foods later in life to prevent bone loss will have the same bone
health as those in countries who have consumed isoflavones throughout
Currently, there is no evidence that soy isoflavones decrease the risk
for fracture. Long-term controlled clinical trials with large numbers
of participants are needed to determine the effect of soy isoflavones
on bone mineral density and fracture risk.
Are there health benefits or concerns about the use of soy products?
Isoflavones act like estrogens in some body tissues and may have anti-estrogen
effects on others. Like estrogen, isoflavones have been shown to help
relieve menopausal symptoms for some women and to reduce cholesterol
Enough evidence has accumulated that the US Food and Drug Administration
allows food manufacturers to make health claims about the supposed
benefits of soy on heart health. The American Heart Association (AHA)
has recommended the inclusion of soy protein as part of a heart-healthy
diet. The AHA concluded that consuming 25 or more grams of soy protein
a day could reduce low-density lipoprotein (LDL) cholesterol (the 'bad'
cholesterol). The beneficial effect of soy protein is thought to be
greatest for those who already have high blood cholesterol, a
known risk factor for heart disease.
For most healthy individuals, moderate soy intake from dietary sources
may be beneficial for overall health including bone health. However,
there are concerns about the potential for isoflavones to increase
the risk for estrogen-sensitive breast cancer. It is important for
individuals, especially those with a personal and/or family history
of breast cancer, to consult a doctor or healthcare provider before
adding soy food products to increase the isoflavone content of their
Are there concerns about the use of isoflavone supplements?
All individuals who are recommended to increase the isoflavone content
of their diets should do so through the use of foods unless directed otherwise by their healthcare provider. There are a growing number of isoflavone supplements readily available over-the-counter without a prescription and others available by prescription. They are available as tablets, concentrates and powders. Isoflavone supplements may have medicinal properties at certain
dosages and therefore should not be used without consultation with your healthcare provider.
What about the use of Ipriflavone? How does it affect bone health?
Ipriflavone is a man-made isoflavone supplement that is touted by its
manufacturers to prevent bone loss in postmenopausal women. It is readily
available as an over-the-counter supplement without a prescription.
In a well-done 4-year European study, it was determined that ipriflavone
did not prevent bone loss or reduce bone turnover in postmenopausal
women. In addition, it did not reduce the risk of spine fractures.
However, in the population studied, ipriflavone caused low lymphocyte
counts that did not return to normal for two years after stopping the
supplement. Lymphocytes are cells that help the body fight infection.
Therefore, the use of ipriflavone is not recommended for osteoporosis
prevention or treatment, and may be otherwise detrimental to one's
If my doctor or healthcare provider recommends that I consume more
soy, how can I increase it in my diet?
For soy recipes on the web, click on: http://www.soyfoods.com/recipes/index.html