All soy comes from soybeans. These naturally grown beans are similar in size to a pea, but contain more protein than other types of beans (legumes). Whole soy is also a good source of carbohydrates, fiber, healthy fats, and many of the vitamins and minerals that are important to good health.
For more information about soy, click to view our Soy Foods and Health document.
Soy is the only commonly consumed plant that is a source of "complete" protein, meaning it contains all nine essential amino acids in amounts sufficient to help meet the body's requirements.
Soy protein is recognized by the United States Department of Agriculture (USDA) as equal in quality to animal. However, unlike many sources of animal protein, soy is low in saturated fat and naturally cholesterol free. 1
Soy protein isolate
Soy protein isolate is generally a dry or powdered food ingredient that has been separated from other components of the soybean. Often it is 90-95% protein and nearly carbohydrate- and fat- free. 2
Soybeans are unique because they are the only commonly eaten food that contains a group of compounds called isoflavones (ahy-soh-FLEY-vohnz or ahy-soh-FLA-vonz). Evidence suggests that isoflavones are at the heart of many of the proposed benefits of soy foods.
Isoflavones are part of a larger group of compounds called phytoestrogens, or plant estrogens, so named because they have a similar chemical structure (though are not the same) as the hormone estrogen.
Isoflavones have been studied for a number of beneficial effects, including a potential role in supporting heart and bone health, minimizing menopausal symptoms, and reducing the risk of some forms of cancer. 3,4,5,6,7,8,9,10,11,12
Soy foods versus soy isoflavone supplements
Soy isoflavone supplements typically only provide isoflavones and generally do not contain considerable amounts of soy protein or other vitamins, minerals, and healthy fats found in whole soy.
Research suggests that there is a difference in the way the body breaks down the isoflavones found in supplements versus the isoflavones found in food. 13,14,15
For more information about soy protein, click to view our Soy Foods and Health document.
Today, European and American governmental agencies recommend that individuals focus on eating more plant-based foods as an eco-friendly way to help decrease the risk of chronic diseases and control weight. 16 Soy foods fit well within these recommendations: Compared to animal protein, soy leaves a much smaller carbon footprint, needing less land and natural resources to grow. Soy provides the same high-quality protein as meat, milk, and eggs, often with less saturated fat and "bad" cholesterol. When chosen in place of animal-based proteins, soy offers other health advantages as well. 17,18,19,20
In the last 20 years, there has been an impressive amount of research conducted on the health effects of soy. Research shows that soy foods:
For more information about the benefits of soy, click to view our Soy Foods and Health document.
Recommendations from the American Heart Association (AHA) to decrease the risk of cardiovascular disease include:
The role of soy in heart health
While no single food can, on its own, prevent heart disease, smart diet and lifestyle choices can have an impact on heart disease risk. Soy foods offer a simple and appealing way to begin making heart smart changes.
Soy protein is versatile, providing the same high quality, complete protein that comes from animal sources (like beef or dairy), but often with less saturated ("bad") fat and cholesterol,21 and research shows that soy protein works to directly lower LDL, or "bad," cholesterol levels. 28,29
Soy's beneficial effect on cholesterol was formally recognized by the United States Food and Drug Administration (FDA) in 1999 when it granted approval for a health claim for soy protein and risk of coronary heart disease.30 This claim states that "25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may help to reduce the risk of heart disease."
To qualify for this claim, a food must contain at least 6.25 grams of soy protein per serving and must be below the specified guidelines for total and saturated fat, cholesterol, and sodium per serving.
The Medifast Connection: Many Medifast Meals meet the requirements to carry the FDA's soy protein and risk of coronary heart disease claim.
For more information about soy and heart health, click to view our Soy Foods and Health document.
There is essentially no scientific evidence that soy foods or soy isoflavones adversely affect thyroid function in healthy individuals.31
For those taking synthetic thyroid hormone (a medication used to treat hypothyroidism), some evidence exists suggesting that eating soy protein may affect the dosage requirement or timing of these medications.31,32,33 This is similar to other common types of food-drug interactions and does not indicate a relationship between soy and thyroid health.34 Patients on thyroid medication should consult with their physician to ensure consistent and effective dosing. General guidelines when taking thyroid medications are to wait one to three hours before or after taking thyroid medication to eat products that contain soy protein,35 have your labs closely monitored, and make sure iodine intake is adequate.
The Medifast Connection: Each Medifast Meal is fortified with an average 20% of the daily value for iodine, providing approximately 100% of the daily value when five Medifast Meals are eaten, as on the Medifast 5 & 1 Plan. Medifast offers a variety of Medifast Meals that are either soy- based or non soy-based.
Note: Soy lecithin, a common food ingredient, is derived from soybeans, but is not known to affect the absorption of thyroid medications.For more information about soy and thyroid health, click to view our Soy Foods and Health document.
Soy and bone health
Some general recommendations for promoting bone health include smoking cessation, an active lifestyle, including weight-bearing exercise as deemed appropriate by your physician, and adequate calcium and vitamin D intake. 36
Long-term population-based studies suggest soy isoflavones may help play a beneficial role in bone health by reducing bone loss in older women. 37,38 Studies among Asian populations found that women who eat the highest amount of soy were approximately one-third less likely to have a fracture when compared to women who eat soy foods infrequently.23,24 At this point, studies suggest a link between soy isoflavones and bone health, but further research is needed before making more definitive conclusions.
The Medifast Connection: All Medifast Meals contain high-quality protein, which may be important for bone health, 39 and are fortified at least 20% of the daily value for both calcium and vitamin D, providing at least 100% of the daily for both of these nutrients when fiveMedifast Meals are eaten.
Soy and breast cancer
Being overweight or obese, especially if excessive weight is gained after menopause, can increase the risk of certain cancers, including breast cancer, 40,41,42,43,44 and is associated with an increased risk of recurrence and a lower survival rate for many cancers, including breast cancer.42,45,46,47,48,49,50
In Asian countries where soy foods are part of the traditional meal plan, rates of breast cancer are much lower than in the United States. Research has shown that Asian women who consume the most soy are about 30% less likely to develop breast cancer than those who eat relatively little soy.25
The protective effects of soy foods are most apparent when soy is eaten in early life (as a child and/or teen).51,52,53,54
Some findings suggest eating soy may help reduce the recurrence and/or the risk of death in women with breast cancer. 55,56 The American Cancer Society (ACS) states breast cancer survivors can safely eat moderate amounts of soy foods.57,58
Despite these encouraging findings, it is recommended that individuals discuss dietary changes with their primary health care provider.
Soy and menopause
Hot flashes are the most common reason given by women for seeking treatment of menopausal symptoms.
Postmenopausal Japanese women are much less likely to report having hot flashes compared to women of Western countries; soy consumption may be one reason.59 In studies where supplements closely matched the natural isoflavone mix found in soybeans, the frequency and severity of hot flashes were consistently reduced.60
Soy and reproductive health
? Overall, soy foods appear to have no significant effects on reproductive hormone levels in women, although eating soy foods may slightly alter the length of the menstrual cycle for some women. 61,62
For more information soy and women's health, soy and bone health, soy and breast cancer, soy and menopause, and soy and reproductive health, click to view our Soy Foods and Health document.
Some men may be reluctant when it comes to "soy foods" because of a mistaken belief that soy, or soy isoflavones, cause feminizing effects in men. This concern is without credible scientific merit. In fact, research has shown that not only are soy foods safe for men to eat, but men may actually benefit by including soy foods in their meal plan. 63,64 Soy foods are a source of healthy, high-quality protein, versatile, and can be used in place of other traditional protein sources, such as meat or dairy.
Soy and heart health
Soy protein is heart healthy: Research shows that soy protein works directly to modestly lower cholesterol levels and may favorably affect other heart disease risk factors not related to cholesterol.28,29,65,66,67,68,69
Soy and prostate health
Men in countries where soy foods are traditionally eaten have lower levels of prostate cancer occurrence and death, and studies show that men who eat the most soy are about 30% less likely to develop prostate cancer than men who eat little soy.
One of soy's isoflavones may help improve prostate cancer outcomes by lowering the levels of an enzyme that allows cancer cells to spread throughout the body. Studies have shown that soy may help decrease the rise of elevated PSA levels; lower PSA levels are associated with a lower risk of prostate cancer development and improved outcomes in those with prostate cancer.26,70,71,72
Soy and reproductive health
There is no meaningful clinical evidence suggesting that soy protein or soy isoflavones lower serum testosterone levels or exert any feminizing effects in men.
The author of a recent publication in the journal Fertility and Sterility, after critically examining the clinical evidence, concluded, "Men can feel confident that making soy a part of their diet will not compromise their virility or reproductive health." 63,64For more information about soy and men's health, soy and heart health, soy and prostate health, and soy and reproductive health, click to view our Soy Foods and Health document.
American Dietetic Association
The American Dietetic Association is your source for trustworthy, science-based food and nutrition information.
The International Food Information Council Foundation provides food safety, nutrition, and healthful eating information to help you make good and safe food choices.
Soy Foods Association of North America
The Soyfoods Association of North America (SANA) is a trusted resource in providing and disseminating credible, science-based information about the health benefits related to soy consumption.
United States Soybean Board
Brought to you by the united soybean board. Browse our library of soy.
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