What are soy isoflavones?
Isoflavones are types of phytoestrogens (plant estrogens) found in soy foods. The isoflavones found in soybeans and soybean products include daidzein, genistein, and glycitein. 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 like estrogen.
What soy foods contain isoflavones?
Edamame (whole soybeans), miso (fermented soybean paste), soy beverages, tempeh (cooked and fermented soy), and tofu (soybean curd) 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 concentrate, 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. The USDA's Agricultural Research Service has compiled a complete database of the isoflavones in soy foods.
What is the isoflavone content of typical US diets?
Most Americans consume only about 1 to 3 milligrams (mg) of isoflavones in their daily diets. That is much less than that consumed in traditional Asian diets which generally include 30 to 60 mg of isoflavones each day. The 2012 Dietary Guidelines for Americans added fortified soy foods as a alternative to dairy foods or protein as part of a healthy plate (choosemyplate.gov) which may lead to an increased intake of soy isoflavones in the United States.
How do soy isoflavones affect bone health?
The current understanding of the role of soy 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 benefit. Some studies have shown small increases in bone mass with isoflavone intake while other studies have shown no 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 people who start eating soy foods later in life to prevent bone loss will have the same impact on bone mass as those in countries who have consumed isoflavones throughout their life.
Currently, there is no evidence that soy isoflavones decrease the risk for osteoporosis-related fractures (broken bones). 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.
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.
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.
The US Food and Drug Administration allows food manufacturers to make health claims about the benefits of soy on heart health. The American Heart Association (AHA) has recommended that soy protein be included as part of a heart-healthy diet. According to the AHA consuming 25 or more grams of soy protein a day may lower 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 possibility for isoflavones to increase the risk for certain medical conditions, such as estrogen-sensitive breast cancer. It is important for people, especially those with a personal and/or family history of breast cancer, to consult their healthcare provider before adding soy food products to increase the isoflavone content of their diets
Are there concerns about the use of isoflavone supplements?
If you are advised by your healthcare provider to increase the isoflavone content of your diet, you should do so by the use of foods rather than supplements, unless directed otherwise by your 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. or 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 supplement that is man-made from the soy isoflavone diadzein. It is readily available over-the-counter without a prescription. Labels on the bottles of ipriflavone often include claims that it prevents bone loss in postmenopausal women. The scientific research findings about ipriflavone and bone health has been conflicting but a large study found that ipriflavone did not prevent bone loss, reduce bone turnover, or reduce the risk of spine fractures in postmenopausal women. In addition, in the population studied, ipriflavone caused women to have low lymphocyte counts. This is of concern since 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 healthcare provider recommends that I consume more soy, how can I increase it in my diet?
Look for recipes containing edamame, fortified soy beverages, tempeh, tofu and other soy foods.