Related Terms

• Daidzein, fabaceae, flavones, flavonoids, genistein, glycitein, kudzu, legumes, leguminosae, phytoestrogens, selective estrogen receptor modulators, SERMs, soy, soy isoflavones, soybeans, tempeh, tofu.

Background

• Isoflavones are a group of molecules that are similar in chemical structure. Isoflavones are produced only by plants in the Fabaceae (also known as Leguminosae) family, frequently called the legume or bean family. Foods that contain high amounts of isoflavones include soy, peanuts, chick peas, alfalfa, fava beans, and kudzu. When consumed by humans, isoflavones may behave like estrogen in the body.

• Estrogen is a hormone that is present in males and females, but women produce much more of it. In women, estrogen is responsible for many of the physical changes that occur when girls begin puberty. It also has many effects related to the monthly menstrual cycle in women as well as in pregnancy. In men, one type of estrogen is important in the development of sperm. Estrogen is present in all people to help maintain normal brain function, to help bones grow, and to contribute to the development of new nerve cells in the brain. The amount of estrogen in the body determines how well this hormone is able to perform its bodily functions.

• Australians first began to investigate that isoflavones may have properties similar to estrogen when they noticed high levels of infertility among sheep who ate large amounts of clover.

• Consuming isoflavones as food or as a supplement may behave as if the amount of estrogen in the body is increased. This is because isoflavones may behave in a way that is very similar to estrogen in the body. Some cancers and other health problems, such as bone loss, may be prevented by consuming a diet that is rich in isoflavone-containing foods.

• However, some experts believe that isoflavones may actually behave as an anti-estrogen. This means that the isoflavones may impair the ability of estrogen to perform its roles in the body. In this case, consuming larger amounts of isoflavones may actually increase the chance of developing some diseases. Isoflavones are sometimes eaten for breast cancer prevention and as a cancer treatment.

• Ultimately, it is unclear if isoflavones have estrogenic or anti-estrogenic properties in the body. Though some experts have concluded that isoflavones may reduce a person's likelihood of developing some health problems, this idea is based on the prevalence of these diseases in cultures where these chemicals are a regular part of the foods in the diet. However, there is not agreement among how much isoflavones may help or harm a patient, because not enough well designed studies in humans have been conducted.

• The potential health risks and benefits of consuming isoflavones is currently under investigation. The isoflavones daidzein, genistein, and glycitein have been the subject of the most research, and are included on the table below.

• Daidzein is more abundant than glycitein, but less abundant than genistein. Daidzein has demonstrated estrogenic properties, but may also be useful in preventing cancer, some forms of heart disease, and osteoporosis. Daidzein has weaker estrogenic properties than glycitein and genistein.

• Glycitein constitutes up to about five to 10 percent of the total isoflavones in most foods. Glycitein has been shown to have estrogenic properties, and may also have antioxidant properties as well. Some researchers believe that glycitein may be useful in treating cancer, some heart diseases, and osteoporosis. Though glycitein is not usually the most abundant isoflavone, it has been demonstrated to have estrogenic properties up to three times greater than genistein and up to twelve times greater than daidzein. Scientists are not sure exactly how glycitein interacts with the body to produce its demonstrated effects.

• Genistein is the most abundant isoflavone in legumes. Similar to daidzein and glycitein, it has been shown to have estrogenic and antioxidant properties. Genistein may also behave as an anti-estrogenic, and decrease the effects of estrogen naturally produced by the body. Genistein may have properties that may make it useful for treating cancer, heart disease, and osteoporosis. Genistein has estrogenic properties that are one third as powerful as glycitein, but four times more powerful than daidzein. Scientists have proposed a number of ways that genistein may behave in the body, but the details are not known at this time.

Amounts of Isoflavones in Foods

• The following table is a summary of information on the amounts of isoflavones in foods. This database was created through a joint effort between the University of Iowa and the U.S. Department of Agriculture (USDA).

• The column on the left is a description of the food. Meatless foods are those that are vegetarian but manufactured to imitate the feel and taste of actual meat products. For instance, "Bacon, meatless" contains no pork, and is imitation bacon made entirely from vegetarian sources.

• The other columns of the table list the milligrams of isoflavones that may be found in 100 grams of food. The three most abundant types of isoflavones, Daidzen, Genistein, and Glycitein, are included. The "total isoflavones" includes a count of all of the isoflavones, often ones other than the three most abundant, in the food.

• After evaluating many samples of food, the researchers averaged the values for each of the four isoflavone categories for each food. The scientific word for this process for finding the average is called "mean."

• Governmental agencies have not agreed on the amount of soy a person should consume every day. However, patients should always talk to their doctor before beginning a new diet.

Isoflavones in Foods

Theory/Evidence

• In 2000, Setchell discussed several studies investigating the effects of eating soy. The author found that the highest concentrations of isoflavones occurred between four and eight hours after eating soy. Isoflavones that were present in solid foods remained in the body longer than those that were eaten as part of a liquid. Based on an analysis of blood levels, the authors proposed that there may be a limit to the concentration of isoflavones that can circulate in the bloodstream.

• In 2001, Setchell proposed that soy isoflavones should be classified as "natural selective estrogen receptor modulators (SERMs)," since these molecules may sometimes behave in ways that are similar to the hormone estrogen.

• In 2006, Sacks et al. reviewed studies investigating the effects of soy protein (which contains isoflavones), and isoflavone supplements (in pill or liquid form) on heart health. The authors did not find a significant difference in certain medical measurements of heart health when study participants consumed soy or isoflavones. While the authors did not recommend taking isoflavone supplements, they did endorse eating foods that are high in isoflavones, such as soy.

Safety

• A qualified healthcare provider should be consulted before making decisions about therapies and/or health conditions.

Author Information

• This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

Bibliography

Natural Standard developed the above evidence-based information based on a thorough systematic review of the available scientific articles. For comprehensive information about alternative and complementary therapies on the professional level, go to www.naturalstandard.com. Selected references are listed below.

1. Centers for Disease Control (CDC). www.cdc.gov

2. Sacks FM, Lichtenstein A, Van Horn L, et al. American Heart Association Nutrition Committee. Soy protein, isoflavones, and cardiovascular health: an American Heart Association Science Advisory for professionals from the Nutrition Committee. Circulation. 2006 Feb 21;113(7):1034-44. View Abstract

3. Setchell KD. Absorption and metabolism of soy isoflavones-from food to dietary supplements and adults to infants. J Nutr. 2000 Mar;130(3):654S-5S. View Abstract

4. Setchell KD. Soy isoflavones--benefits and risks from nature's selective estrogen receptor modulators (SERMs). J Am Coll Nutr. 2001 Oct;20(5 Suppl):354S-362S; discussion 381S-383S. View Abstract

5. United States Department of Agriculture. www.usda.gov