Soy (Glycine max [L.] Merr.)


Soy is a subtropical plant, native to southeastern Asia. This member of the pea family 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. states produce approximately half of the world's supply of soybeans.
Soy contains protein, isoflavones, and fiber, all thought to provide health benefits. Soy is an excellent source of dietary protein, including all essential amino acids. Soy is also a source of lecithin or phospholipid. Soy isoflavones and lecithin 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."
Common sources of soy isoflavones include roasted soybean, green soybean, soy flour, tempeh, tofu, tofu yogurt, soy hot dogs, miso, soy butter, soy nut butter, soy ice cream, soy milk, soy yogurt, tofu pups®, soy cheese, bean curd, seitan, and soy noodles. Soybean flour is found in Spanish sausage products (chorizo, salchichon, mortadella, and boiled ham), doughnuts, and soup stock cubes. Although processed soy foods (e.g., veggie burgers, tofu pups®, meatless dinner entrees, chicken-free nuggets, soy "ice creams" and energy bars) are usually high in protein, they typically contain lower levels of isoflavones.
Soy protein has also been investigated for benefit in terms of heart disease risk factors, reducing menopausal symptoms, weight loss, arthritis, brain function, and exercise performance. Dietary soy may decrease the risk of breast cancer in women and prostate cancer in men, as well as other types of cancers. In general, the supportive evidence for use of phytoestrogens as treatments for menopause, heart disease, bone disease, weight loss, and cancer is limited. The use of soy formula has been investigated in the treatment of diarrhea in infants and is an effective and safe alternative to cow's milk formula in most infants.

Related Terms

Abalon®, beta-conglycinin, bioactive peptides, bowman-birk inhibitor (BBI), calcium, conglycinin, coumestrol, daidzein, daizuga-cha (Japanese), dark soy sauce, dietary soy protein, edamame, equol, Fabaceae, Fibrim®, fish oil, flavonoids, folate, fortified soymilk, frijol de soya, functional proteins, genistein, genistin, Glycine max, Glycine max AT, glycinin, greater bean, guar gum, haba soya, hydrolyzed soy protein, Hyprovit®, iron, isoflavone, isoflavones, isoflavonoid, Isomil®, kuromame-cha (Japanese), kuromame-cha Gold (Japanese), kuromame-soymilk drink (Japanese), lecithin, legume, lignans, magnesium, margarine, miso, Mull-Soy®, natto, Nursoy®, okara, phosphatidylserine, phosphorus, phytate, phytoestrogen, plant estrogen, potassium, Previna®, ProSobee®, PtdSer, Purina 660, shoyu, shoyu polysaccharides, soja, sojabohne, soya, soya-based food, soya protein, soya saponins, soya sauce, soybean, soybean-barley paste, soybean oil, soy concentrates, Soy Enfamil®, soy fiber, soy flour, soy food, soy isoflavones, soy isolates, soy lecithin, soymilk, soy nuts, soy oil, soy phosphatidylcholine complex (IdB 1016), soy phosphatidylinositol (PI), soy product, soy protein, soy protein isolate, soy sauce, S-PtdSer, Supro®, Supro 660®, Supro 675®, Ta-tou, tempeh, texturized vegetable protein, tofu, yuba.
Note: Ipriflavone, a synthetic isoflavone, has been studied as a possible way to treat or prevent bone loss in post-menopausal women. This monograph concentrates on natural soy. Ipriflavone is discussed separately. Soy isoflavones, genistein and daidzein, have been studied as treatments for various conditions. This monograph concentrates on soy protein or foods containing soy protein. Isoflavones are discussed separately. Soy lecithin is derived from the processing of soybeans. It is a mixture of fatty substances separated from soybean oil and used as a food additive. Its chemical name is phosphatidylcholine and contains the constituents of choline, phosphoric acid, glycerin, and fatty acids. Soy lecithin is discussed in a separate monograph. Soybean oil and soy-derived sterols are not specifically discussed.

evidence table

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 (Grade: A)
Soy products, such as tofu, are high in protein and are an acceptable source of dietary protein.
High cholesterol (Grade: A)
Human research reports that adding soy protein to the diet can moderately decrease total cholesterol and low-density lipoprotein ("bad" cholesterol). The most benefit has been seen when all animal protein is substituted with soy, especially in soy products that contain isoflavones. The reductions in cholesterol may last as long as the diet is continued.
Diarrhea (acute) in infants and young children (Grade: B)
Research reports that infants with diarrhea who are fed soy formula have less diarrhea than those fed milk formula. This only applies to children that are unable to eat solid food. Further research is needed before a conclusion can be made. Parents are advised to speak with qualified healthcare providers if their infants experience prolonged diarrhea, become dehydrated, develop signs of infections (such as fever), or have blood in the stool. A healthcare provider should be consulted for current breastfeeding recommendations and to suggest long-term formulas that provide enough nutrition.
High blood pressure (Grade: B)
Research in humans generally shows that soy lowers blood pressure. Further research is needed to determine the ideal soy preparation for lowering blood pressure.
Menopausal symptoms (hot flush) (Grade: B)
Research shows that soy reduces hot flash occurrence in menopausal women. Further research is needed before a strong conclusion can be made.
Allergies (prevention of food allergies) (Grade: C)
Soy formulas are commonly used by infants with sensitivities to milk-based formulas. There is currently little evidence to support the use of soy formulas for preventing food allergies. Further research is needed in this field.
Antioxidant (Grade: C)
There is some evidence in support of soy increasing antioxidant status in humans. In general, diets high in plant foods may offer antioxidant benefits. Further research is required in this field before conclusions can be made.
Bowel/intestinal disorders (Grade: C)
The effect of soy on ulcers in the bowel/intestinal tract has been examined in limited study. Overall, the effects of soy products appear beneficial. Further study is required before conclusions can be made.
Cancer (prevention and treatment) (Grade: C)
Limited human research shows that soy may decrease the risk of cancer, including breast, prostate, and colon cancer. However, confounding factors including dietary and lifestyle habits, culture, and genetics must be considered. Further research is needed before a conclusion can be made.
Cognitive function (Grade: C)
It is unclear if soy supplementation in postmenopausal women can improve cognitive function. Results from studies are mixed. Further research is necessary.
Crohn's disease (Grade: C)
From limited human research, it is unclear if soy helps with Crohn's disease. Further research is needed before a conclusion can be made.
Cyclical breast pain (Grade: C)
Limited research shows that soy may decrease cyclical breast pain, which is pain linked to the menstrual cycle. Further research is needed to draw conclusions.
Diabetes (Grade: C)
Human research demonstrates mixed results of soy products for blood sugar levels in people with type 2 diabetes. Overall, better quality research is needed in this area.
Exercise performance (Grade: C)
Soy protein has been investigated as a source of protein with potential for benefit in exercise performance. In general, research findings suggest soy protein is better than a lack of protein but is unlikely to be superior to other sources of protein. Further research is required in this field.
Fibromyalgia (Grade: C)
Limited evidence shows that soy lacks benefit for physical function and depression symptoms in fibromyalgia. Further research in this area is needed before any firm conclusions can be made.
Gallstones (Grade: C)
There is insufficient evidence regarding the use of soy as a therapy for gallstones. Further research is needed before a conclusion can be made.
Heart disease (Grade: C)
Research suggests cholesterol-lowering effects of dietary soy, which in theory, may reduce the risk of heart problems. However, in limited research soy lacked an effect on blood vessel function and increased the levels a heart disease risk marker. Further investigation is needed before a conclusion can be made.
Infantile colic (Grade: C)
There is currently a lack of scientific evidence regarding the use of soy formula for fussiness and gas in infants with cow's milk allergy. Further research is warranted.
Inflammation (Grade: C)
Sufficient evidence is lacking regarding the use of soy protein for inflammation associated with hemodialysis (a treatment given when kidneys fail, to remove waste from the blood). Further research is needed.
Iron deficiency anemia (Grade: C)
There is currently a lack of sufficient evidence regarding the use of soy-based formula in the treatment of iron deficiency anemia in children. Further research is needed.
Kidney disease (Grade: C)
Sufficient evidence is lacking regarding the use of soy in the treatment of kidney diseases, such as nephrotic syndrome. Further research is necessary. People with kidney disease should speak with their healthcare providers about the recommended amounts of dietary protein because soy is a high-protein food.
Menopausal symptoms (non hot-flush) (Grade: C)
Overall, evidence suggests that soy products containing isoflavones may help reduce various menopausal symptoms. More study is needed to confirm this use.
Menstrual migraine (Grade: C)
An herbal combination containing soy may help prevent menstrual migraine attacks. Further research is needed before a conclusion can be made.
Metabolic syndrome (Grade: C)
Treatment with soy protein and soy nuts was evaluated in patients with metabolic syndrome. Benefits were found in terms of decreased cholesterol levels from consuming soy. Further research is required in this field to draw conclusions.
Motility disorders (problems with digestion) (Grade: C)
In limited research, the addition of soy polysaccharide to non-regular diets improved stool consistency. It is unclear if soy polysaccharide would be superior to other fiber sources in this regard. Further research is warranted.
Osteoarthritis (Grade: C)
Osteoarthritis is a form of arthritis caused by the breakdown of cartilage and resulting in symptoms of pain and decreased range of motion of joints. Early research suggests that intake of soy protein may be associated with reduced symptoms of osteoarthritis. Further research is needed before conclusions can be made.
Physical functioning and well-being in the elderly (Grade: C)
Early evidence suggests that increased dietary intake of soy is associated with a decreased risk of physical disability in healthy older women. Further high quality research is needed for conclusions to be made.
Premenstrual syndrome (PMS) (Grade: C)
Sufficient evidence is lacking regarding the use of soy in managing symptoms of PMS. Further high-quality clinical research is needed in this area before any firm conclusions can be made.
Rheumatoid arthritis (Grade: C)
There is currently insufficient evidence regarding the use of soy as a treatment for rheumatoid arthritis. High-quality clinical research is needed in this area.
Skin aging (Grade: C)
Research shows that combination products containing soy extract have demonstrated improvements in wrinkles and skin quality. More research is needed with soy products alone before a conclusion can be made.
Skin damage caused by the sun (Grade: C)
A soy moisturizing cream may help improve signs of sun damage, including discoloration, blotchiness, dullness, fine lines, and overall texture. Because the cream contained other ingredients besides soy, more research with soy alone is needed.
Spinal cord injury (Grade: C)
Whey protein has traditionally been used as a protein source to increase body strength. Limited research investigated whether soy protein could be used to increase walking performance in patients with incomplete spinal cord injury. Further research is needed to make a conclusion.
Thyroid disorders (Grade: C)
Early research suggests that soy supplements lack an effect on thyroid function. More research is needed.
Tuberculosis (Grade: C)
According to early research, soy may improve tolerance of antimicrobial drugs that are used to treat tuberculosis. Further research is needed to make conclusions.
Weight gain (infants) (Grade: C)
In limited study, weaning infants with cow's milk allergy to soy based formula resulted in reduced weight for age as compared with formulas containing hydrolyzed (broken down) proteins. Further research is required in this field.
Weight loss (Grade: C)
Some research suggests that soy might be as effective as skim milk and more effective than a low-calorie diet alone in reducing weight. Other research has reported conflicting results. Further research is needed before a conclusion can be made.
Osteoporosis (Grade: F)
Human research shows that soy lacks an effect on bone mineral density in post-menopausal women and healthy adults. However, more research is needed.