Soy

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?

Miso, 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 their life.

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 levels.

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 diets

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 health.

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