Soy is a general term for products made from soybeans, the most widely used beans in the world. Soy products include tofu, tempeh, soy oil, natto, miso, soymilk, and edamame.
Soy is a complete protein, meaning that it contains all of the essential amino acids that the body needs. In this sense, soy is different from most vegetable proteins and is nutritionally equivalent to animal protein. This makes it an optimal meat alternative for people practicing vegetarianism or veganism. Soy also contains no cholesterol and is low in saturated fat, unlike many sources of animal protein. Soy is a heart-healthy food choice, and many soy products meet the U.S. Food and Drug Administration (FDA) requirements to feature that claim on their product labels.
Amount of soy protein
1 cup (8 ounces) soymilk
4 ounces tofu
1 soy burger
1 soy protein bar
1 soy sausage link
V cup roasted soy nuts
Soy is believed to promote cardiovascular health. Many other health claims are also made for soy, including that it:
Some of these claims remain unsubstantiated, are under review, or are in dispute; further research is needed.
Soybeans are the seeds of the plant Glycine max. This plant is native to China, where it has been cultivated for about 13,000 years. From China, soybeans gradually spread to other areas of Asia, where soy is a major part of the diet. Intense breeding has produced a number of variants (cultivars) of the original plant, some of which have a higher oil content and others that have a higher protein content. Soybeans may be green, yellow, brown, or black in color, but all variations are edible.
Soybeans were introduced into the United States in the mid-1700s. George Washington Carver (1864–1943) experimented with them before he began his famous nutrition research on peanuts. In 2011, the United States was the world's largest grower of soybeans, with 75 million acres planted, producing more than 3 billion bushels of soybeans for a total cash value of approximately $40 billion. However, most of the soybeans grown in the United States are pressed to make soy oil. After the oil is extracted, the beans are ground into meal and used as livestock feed.
Soy is a nutrient-dense food, and it is the least expensive source of complete dietary protein. It is relatively low in calories and contains no cholesterol, little saturated fat, and no trans fat. One cup (172 g) of cooked soybeans has about 300 calories and contains the following nutrients (the percent DV is of the daily requirement that one cup of cooked soybeans meets for the average adult):
Fresh soybeans can be cooked briefly in boiling water or toasted before eating. Dried beans need to be soaked overnight before cooking and require relatively long cooking times. Soybeans can also be pressed to make soy oil, but the most familiar soy products come from soybeans that have been processed to give them a variety of textures and make them easier to use in cooking:
In October 1999, the FDA decided that well-designed, well-controlled, repeatable research studies had shown that soy was a heart-healthy food that could help to decrease the risk of developing cardiovascular disease. Since that date, the FDA has allowed products that contained at least 6.25 g of soy per serving to make the following health claim on their label: “25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease.” This endorsement applies only to complete soy products, not to soy-based dietary supplements. The American Heart Association (AHA) also approves soy as a food that can reduce the risk of heart disease.
Soy may also help in weight loss, because it can be used as a substitute for higher-calorie meat. If soy is substituted for meat on a regular basis, the reduction in calories can be significant:
Some health controversies about soy center on compounds called isoflavones that are found in abundance in soybeans. These compounds have a chemical structure similar to the female hormone estrogen. Several health effects, both positive and negative, have been attributed to isoflavones. In 2006, the AHA concluded that isoflavones are not the cause of the cholesterol-lowering, heart-healthy properties of soy and that dietary supplements containing soy-derived isoflavones do not have the same cardiovascular benefits as whole soy.
Also because of their estrogen-like structure, isoflavones from soy have been touted as a dietary supplement that will help prevent symptoms of menopause such as hot flashes. The low rate of menopausal symptoms among Chinese and Japanese women has been linked to their high soy intake; however, a committee of the AHA investigating isoflavones found that they had no effect on hot flashes.
A far bigger health question concerns the relationship between isoflavones and cancer. Soy has been linked to the treatment and prevention of several cancers, including breast and prostate cancers, but study results have been inconclusive. Soy consumption may lower levels of prostate-specific antigen (PSA) in men, which are typically higher in men with prostate cancer, but further research is needed. The AHA committee found that despite claims that soy isoflavone supplements can treat and prevent breast, endometrial, and uterine cancers in women and prostate cancer in men, there was no evidence to suggest that this treatment was safe or effective. On the other hand, there was also no evidence that soy increased the chances of postmenopausal women developing breast cancer, as some experts have suggested. Soy may even help reduce the risk of recurrence in breast cancer survivors. The American Institute for Cancer Research (AICR) also funds studies researching the relationship between cancer prevention and soy isoflavones, among other foods and supplements. The AICR recognizes that the link between soy and breast cancer prevention has been found only in animal laboratory experiments and that the results have been inconsistent. However, there is no harm associated with moderately consuming soy products, and the AICR suggests safe limits of about two to three servings per day.
Although soy is often thought of as a benign food, some people are allergic to soy. It has been estimated that in the United States about 1.1% of children are allergic to soy, compared to about 3.4% who are allergic to cow's milk. An international study of infants given soy-based formula found an allergy rate of about 0.5%.
Soy contains compounds called goitrogens. Goitrogens interfere with the body's ability to absorb or use iodine. The goitrogens in soy should not cause problems with iodine uptake in healthy people, but people with thyroid deficiencies should discuss with their healthcare provider whether they should limit soy in their diet.
Women taking tamoxifen (Nolvadex) or other anti-estrogen medications, used to treat and prevent breast cancer in high-risk women, should not consume soy products.
Some studies have suggested that high soy consumption may produce adverse side effects in men, including decreased testosterone production and lowered sperm count. These claims are unsubstantiated, however, and men would likely have to consume excessive quantities of soy to see any side effects.
Soy is considered safe for children to consume, and several varieties of soy infant formula are available. If parents are giving children soy products instead of cow's milk or meat, they should consult with their pediatricians to ensure that their children are receiving enough vitamins and minerals, especially iron, found in meat, and vitamin D and calcium, found in cow's milk.
See also Cancer-fighting foods ; Celiac disease ; Diet and disease prevention ; Infant nutrition ; Osteoporosis diet ; Veganism .
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Messina, M. “Soybean Isoflavone Exposure Does Not Have Feminizing Effects on Men: A Critical Examination of the Clinical Evidence.” Fertility and Sterility 93, no. 7 (May 1, 2010): 2095–104.
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Academy of Nutrition and Dietetics, 120 South Riverside Plz., Ste. 2000, Chicago, IL, 60606, (312) 899-0040, (800) 877-1600, email@example.com, http://www.eatright.org .
Center for Nutrition Policy and Promotion, U.S. Department of Agriculture, 3101 Park Center Dr., 10th Fl., Alexandria, VA, 22302, (703) 305-7600, Fax: (703) 305-3300, firstname.lastname@example.org, http://www.cnpp.usda.gov .
Soyfoods Association of North America, 1050 17th Street NW, Ste. 600, Washington, DC, 20036, (202) 659-3520, Fax: (202) 659-3522, email@example.com, http://www.soyfoods.org .
Helen M. Davidson, MA
Revised by Tish Davidson, AM