Soy is a subtropical plant, native to southeastern Asia. This member of the pea family (Fabaceae) grows from one to five feet tall and forms clusters of three to five pods, each containing two to four beans per pod. Soy has been a dietary staple in Asian countries for at least 5,000 years, and during the Chou dynasty in China (1134-246 B.C.), fermentation techniques were discovered that allowed soy to be prepared in more easily digestible forms such as tempeh, miso, and tamari soy sauce. Tofu was invented in 2nd Century China.
Soy was introduced to Europe in the 1700s, and to the United States in the 1800s. Large-scale soybean cultivation began in the United States during World War II. Currently, Midwestern U.S. growers produce approximately half of the world's supply of soybeans.
Soy and components of soy called "isoflavones" have been studied scientifically for numerous health conditions. Isoflavones (such as genistein) are believed to have estrogen-like effects in the body, and as a result are sometimes called "phytoestrogens." In laboratory studies, it is not clear if isoflavones stimulate or block the effects of estrogen, or both (acting as "mixed receptor agonists/antagonists").
Coumestrol, daidzein, edamame, frijol de soya, genistein, greater bean, haba soya, hydrolyzed soy protein, isoflavone, isoflavonoid, legume, natto, phytoestrogen, plant estrogen, shoyu, soja, sojabohne, soya, soya protein, soybean, soy fiber, soy food, soy product, soy protein Ta-tou, texturized vegetable protein.
These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Dietary source of protein
Soy products such as tofu are high in protein and are an acceptable source of dietary protein.
Numerous human studies report that adding soy protein to the diet can moderately decrease blood levels of total cholesterol and low-density lipoprotein ("bad" cholesterol). Small reductions in triglycerides may also occur, while high-density lipoprotein ("good" cholesterol) does not seem to be significantly altered.
Diarrhea (acute) in infants and young children
Numerous studies report that infants and young children (ages 2 to 36 months) with diarrhea who are fed soy formula experience fewer bowel movements per day and fewer days of diarrhea. This research suggests soy to have benefits over other types of formula, including cow milk-based solutions. The addition of soy fiber to soy formula may increase the effectiveness. Better quality research is needed before a strong recommendation can be made.
Menopausal hot flashes
Soy products containing isoflavones have been studied for the reduction of menopausal symptoms such as hot flashes. The scientific evidence is mixed in this area, with several human trials suggesting reduced number of hot flashes and other menopausal symptoms, but more recent research reporting no benefits. Overall, the scientific evidence does suggest benefits, although better quality studies are needed in this area in order to form a firm conclusion.
Breast cancer prevention
Several large population studies have asked women about their eating habits, and reported higher soy intake (such as dietary tofu) to be associated with a decreased risk of developing breast cancer. However, this type of research can only be considered preliminary, because people who choose to eat soy may also partake in other lifestyle decisions that may lower the risk of cancer. These other habits, rather than soy, could theoretically be the cause of the benefits seen in these studies (for example, lower fat intake, more frequent exercise, lack of smoking).
Genistein, an isoflavone found in soy, has been found in laboratory and animal studies to possess anti-cancer effects, such as blocking new blood vessel growth (anti-angiogenesis), acting as a tyrosine kinase inhibitor (a mechanism of many new cancer treatments), or causing cancer cell death (apoptosis). In contrast, genistein has also been reported to
Dietary soy protein has not been shown to affect long-term cardiovascular outcomes such as heart attack or stroke. Research does suggest cholesterol-lowering effects of dietary soy, which in theory may reduce cardiovascular risk. Soy has also been studied for blood pressure-lowering and blood sugar-reducing properties in people with type 2 diabetes, although the evidence is not definitive in these areas. Further investigation is needed before a recommendation can be made.
A recent study suggests that isoflavone supplementation in postmenopausal women may have favorable effects on cognitive function, particularly verbal memory. Further research is necessary before a firm conclusion can be drawn.
Colon cancer prevention
There is not enough scientific evidence to determine if dietary intake of soy affects the risk of developing colon cancer. Study results are mixed and more research is needed before a recommendation can be made.
Due to limited human study, there is not enough evidence to recommend for or against the use of soy as a therapy in preventing Crohn's disease. Further research is needed before a recommendation can be made.
Cyclical breast pain
It has been theorized that the presence in soy of "phytoestrogens" (plant-based compounds with weak estrogen-like properties) such as isoflavones may be beneficial to pre-menopausal women with cyclical breast pain. However, due to limited human study, there is not enough evidence to recommend for or against the use of dietary soy protein as a therapy for this condition.
Diarrhea in adults
Due to limited human study, there is not enough evidence to recommend for or against the use of soy-polysaccharide/fiber in the treatment of diarrhea. Further research is needed before a recommendation can be made.
Endometrial cancer prevention
There is not enough scientific evidence to determine if dietary intake of soy affects the risk of developing endometrial cancer.
Due to limited human study, there is not enough evidence to recommend for or against the use of soy as a therapy in cholelithiasis. Further research is needed before a recommendation can be made.
High blood pressure
Due to limited human study, the effects of dietary soy on blood pressure are not clear. Further research is necessary before any recommendation can be made.
Kidney disease (chronic renal failure, nephrotic syndrome, proteinuria)
Due to limited human study, there is not enough evidence to recommend for or against the use of soy in the treatment of kidney diseases such as nephrotic syndrome. People with kidney disease should speak to their healthcare provider about recommended amounts of dietary protein, and should bear in mind that soy is a high protein food.
One study of a phytoestrogen combination showed a reduced the number of migraine attacks suffered. Further research is needed before a recommendation can be made.
Obesity, weight reduction
Due to limited human study, there is not enough evidence to recommend for or against the use of soy for weight reduction. Further research is needed before a recommendation can be made.
Osteoporosis, post-menopausal bone loss
It has been theorized that the presence in soy of "phytoestrogens" (plant-based compounds with weak estrogen-like properties) such as isoflavones may increase bone mineral density in post-menopausal women and reduce the risk of fractures. However, most studies have not been well designed or reported. Until better research is available, a firm conclusion cannot be drawn. Individuals at risk for osteoporosis should speak with a qualified healthcare provider about the therapeutic options for increasing bone mineral density.
Prostate cancer prevention
Preliminary research has examined the effects of dietary soy intake on prostate cancer development in humans, but results have not been conclusive. Better study is needed before a recommendation can be made.
Preliminary study suggests that intake of soy products may be associated with a reduced risk of death from stomach cancer. Further investigation is needed before a conclusion can be drawn.
Type 2 diabetes
Several small studies have examined the effects of soy products on blood sugars in people with type 2 ("adult-onset") diabetes. Results are mixed, with some research reporting decreased blood glucose levels, and other trials noting no effects. Overall, research in this area is not well designed or reported, and better information is needed before the effects of soy on blood sugars can be clearly described.