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Soy

 

Natural Standard Monograph, Copyright © 2014 (www.naturalstandard.com). Commercial distribution prohibited. This monograph is intended for informational purposes only, and should not be interpreted as specific medical advice. You should consult with a qualified health care professional before making decisions about therapies and/or health conditions.

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.

Background

  • 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.

Evidence

 

Uses based on scientific evidence 

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 professional.

Grade* 

Dietary source of protein 

Soy products, such as tofu, are high in protein and are an acceptable source of dietary protein.

A 

High cholesterol 

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.

A 

Diarrhea (acute) in infants and young children 

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.

B 

High blood pressure 

Research in humans generally shows that soy lowers blood pressure. Further research is needed to determine the ideal soy preparation for lowering blood pressure.

B 

Menopausal symptoms (hot flush) 

Research shows that soy reduces hot flash occurrence in menopausal women. Further research is needed before a strong conclusion can be made.

B 

Allergies (prevention of food allergies) 

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.

C 

Antioxidant 

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.

C 

Bowel/intestinal disorders 

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.

C 

Cancer (prevention and treatment) 

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.

C 

Cognitive function 

It is unclear if soy supplementation in postmenopausal women can improve cognitive function. Results from studies are mixed. Further research is necessary.

C 

Crohn's disease 

From limited human research, it is unclear if soy helps with Crohn's disease. Further research is needed before a conclusion can be made.

C 

Cyclical breast pain  

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.

C 

Diabetes 

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.

C 

Exercise performance  

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.

C 

Fibromyalgia  

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.

C 

Gallstones  

There is insufficient evidence regarding the use of soy as a therapy for gallstones. Further research is needed before a conclusion can be made.

C 

Heart disease 

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.

C 

Infantile colic 

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.

C 

Inflammation  

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.

C 

Iron deficiency anemia 

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.

C 

Kidney disease  

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.

C 

Menopausal symptoms (non hot-flush) 

Overall, evidence suggests that soy products containing isoflavones may help reduce various menopausal symptoms. More study is needed to confirm this use.

C 

Menstrual migraine 

An herbal combination containing soy may help prevent menstrual migraine attacks. Further research is needed before a conclusion can be made.

C 

Metabolic syndrome 

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.

C 

Motility disorders (problems with digestion) 

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.

C 

Osteoarthritis 

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.

C 

Physical functioning and well-being in the elderly 

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.

C 

Premenstrual syndrome (PMS) 

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.

C 

Rheumatoid arthritis 

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.

C 

Skin aging 

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.

C 

Skin damage caused by the sun 

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.

C 

Spinal cord injury 

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.

C 

Thyroid disorders 

Early research suggests that soy supplements lack an effect on thyroid function. More research is needed.

C 

Tuberculosis 

According to early research, soy may improve tolerance of antimicrobial drugs that are used to treat tuberculosis. Further research is needed to make conclusions.

C 

Weight gain (infants) 

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.

C 

Weight loss 

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.

C 

Osteoporosis 

Human research shows that soy lacks an effect on bone mineral density in post-menopausal women and healthy adults. However, more research is needed.

F 

 

*Key to grades: 

A: Strong scientific evidence for this use;
B: Good scientific evidence for this use;
C: Unclear scientific evidence for this use;
D: Fair scientific evidence against this use (it may not work);
F: Strong scientific evidence against this use (it likely does not work).

For full grading rationale, click here.

Uses based on tradition or theory 

The below uses are based on tradition or scientific theories. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified health care professional

Alzheimer's disease, anorexia, anti-aging, antifungal, asthma, atherosclerosis (hardening of the arteries), ADHD, blood clots, bone fractures, breast enlargement, clogged arteries, colon inflammation, constipation, cystic fibrosis (mucus build-up in organs), diabetic nerve pain, estrogen-like activity, fall prevention, fever, growth, headache, hepatitis (liver inflammation), immune function, improving health outcomes, infertility, insect repellant, malnutrition, melasma (skin discoloration), nosebleed, polycystic ovary syndrome (cysts in ovaries), prostate enlargement (BPH), respiratory problems (cough, phlegm), vaginitis (vaginal inflammation), wound healing.


Safety

The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare professional before starting a new therapy. Consult a healthcare professional immediately if you experience side effects.

Allergies

  • Avoid with a known allergy to soy, any of its parts, or members of its plant family.
  • Soy may act as a food allergen similar to milk, eggs, peanuts, fish, and wheat. Symptoms of an allergic reaction range from a runny nose, to inflammation of the digestive tract to a sudden drop in blood pressure.

Side Effects and Warnings

  • Soy is likely safe when used in the diet in adults, children, and infants, although maximum duration is unknown. Soy protein has been safely used for up to one year. Soy formula has been safely used in full-term infants.
  • Soy may cause atopic eczema (skin problems), asthma, bad taste, bleeding, bloating, constipation, damage to pancreas, diarrhea, goiters (enlarged neck due to increased thyroid size), growth failure, fatigue, immune changes, increased heart rate, insomnia, intestinal inflammation, loose stool, menstrual changes, migraine, nausea, stomach pain, and vomiting.
  • Use cautiously in people with hormone-sensitive cancers such as breast, ovarian, or uterine cancer, or hormone-sensitive conditions such as endometriosis.
  • Soy may increase the risk of bleeding. Caution is advised in people with bleeding disorders or taking drugs that may increase the risk of bleeding. Dosing adjustments may be necessary.
  • Soy may lower blood sugar levels. Caution is advised in people with diabetes or low blood sugar, and in those taking drugs, herbs, or supplements that affect blood sugar. Blood sugar levels may need to be monitored by a qualified healthcare professional, including a pharmacist, and medication adjustments may be necessary.
  • Soy may cause high blood pressure. Caution is advised in people taking drugs or herbs and supplements that alter blood pressure.
  • Because soy contains estrogen like chemicals, the effects of other agents believed to have estrogen-like properties may be altered.
  • Soy may interfere with the way the body processes certain drugs using the liver's "cytochrome P450" enzyme system.
  • Use cautiously in people who have anemia, cystic fibrosis, or disorders of the thyroid, stomach, intestine, immune system, or heart.
  • Avoid with a known allergy to soy, any of its parts, or members of its plant family.
  • Avoid soy at levels higher than normally consumed in food if the person is pregnant or lactating, has cancer or is at risk for cancer, or is taking medications.

Pregnancy and Breastfeeding

  • Soy as a part of the regular diet is traditionally considered to be safe during pregnancy and breastfeeding, although scientific research is limited in these areas.
  • Recent study demonstrates that isoflavones are transferred through breast milk from mothers to infants. In non-human study, high doses of isoflavones resulted in tumors and reproductive changes in offspring. Avoid high doses of soy or soy isoflavones in humans.

Interactions

Most herbs and supplements have not been thoroughly tested for interactions with other herbs, supplements, drugs, or foods. The interactions listed below are based on reports in scientific publications, laboratory experiments, or traditional use. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare professional before starting a new therapy.

Interactions with Drugs

  • Soy may increase the risk of bleeding when taken with drugs that increase the risk of bleeding. Some examples include aspirin, anticoagulants ("blood thinners") such as warfarin (Coumadin®) or heparin, anti-platelet drugs such as clopidogrel (Plavix®), and non-steroidal anti-inflammatory drugs such as ibuprofen (Motrin®, Advil®) or naproxen (Naprosyn®, Aleve®).
  • Soy may lower blood sugar levels. Caution is advised when using medications that may also lower blood sugar. People taking drugs for diabetes by mouth or insulin should be monitored closely by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.
  • Soy may cause high blood pressure. Caution is advised in people taking drugs that affect blood pressure.
  • Soy may interfere with the way the body processes certain drugs using the liver's "cytochrome P450" enzyme system. As a result, the levels of these drugs may be increased in the blood, and may cause altered effects or potentially serious adverse reactions. People using any medications should check the package insert, and speak with a qualified healthcare professional, including a pharmacist, about possible interactions.
  • Because soy contains estrogen like chemicals, the effects of other agents believed to have estrogen-like properties may be altered.
  • Soy may also potentially interact with agents for the skin, agents taken for bone health, agents taken for cancer, diarrhea, high cholesterol, heart disorders, or weight loss, agents that affect the nervous or immune system, Alzheimer's agents, antibiotics, aromatase inhibitors, calcitriol, diuretics (water pills), hormonal agents, iron salts, indomethacin, insect repellants, progestins, selective estrogen receptor modifiers (SERMs), stomach or intestine agents, thyroid hormones, tibolone.

Interactions with Herbs and Dietary Supplements

  • Soy may increase the risk of bleeding when taken with herbs and supplements that are believed to increase the risk of bleeding. Multiple cases of bleeding have been reported with the use of Ginkgo biloba, and fewer cases with garlic and saw palmetto. Numerous other agents may theoretically increase the risk of bleeding, although this has not been proven in most cases.
  • Soy may lower blood sugar levels. Caution is advised when using herbs and supplements that may also lower blood sugar. People taking drugs for diabetes by mouth or insulin should be monitored closely by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.
  • Soy may cause high blood pressure. Caution is advised in people taking herbs and supplements that affect blood pressure.
  • Soy may interfere with the way the body processes certain herbs or supplements using the liver's "cytochrome P450" enzyme system. As a result, the levels of other herbs or supplements may be altered in the blood. It may also alter the effects that other herbs or supplements possibly have on the P450 system.
  • Because soy contains estrogen like chemicals, the effects of other agents believed to have estrogen-like properties may be altered.
  • Soy may also potentially interact with Alzheimer's herbs and supplements, antibacterials, antioxidants, avocado, beta-sitosterol, black cohosh, branched-chain amino acids, calcium, diuretics (increase urine volume), flaxseed, ginseng, green tea, herbs and supplements for osteoporosis, herbs and supplements for the skin, herbs and supplements taken for cancer, diarrhea, high cholesterol, heart disorders, or weight loss, herbs and supplements that affect the nervous, digestive, or immune systems, hormonal herbs and supplements, hormonal replacement therapy, insect repellants, iron, isoflavones, lecithin, lycopene, magnesium, magnolia bark extract, manganese, oats, phosphorus, phytoprogestins, plant sterols, probiotics, resveratrol, seaweed, selenium, spirulina, thyroid hormones, vitamin C and D, zinc.

Authors

Selected References

Natural Standard developed the above evidence-based information based on a 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. Anderson JW and Bush HM. Soy protein effects on serum lipoproteins: a quality assessment and meta-analysis of randomized, controlled studies. J.Am.Coll.Nutr. 2011;30(2):79-91.
  2. Beavers DP, Beavers KM, Miller M, et al. Exposure to isoflavone-containing soy products and endothelial function: a Bayesian meta-analysis of randomized controlled trials. Nutr.Metab Cardiovasc.Dis. 2012;22(3):182-191.
  3. Bruyas-Bertholon V, Lachaux A, Dubois JP, et al. [Which treatments for infantile colics?]. Presse Med. 2012;41(7-8):e404-e410.
  4. Clement YN, Onakpoya I, Hung SK, et al. Effects of herbal and dietary supplements on cognition in menopause: a systematic review. Maturitas 2011;68(3):256-263.
  5. Dong JY, Tong X, Wu ZW, et al. Effect of soya protein on blood pressure: a meta-analysis of randomised controlled trials. Br.J.Nutr. 2011;106(3):317-326.
  6. Dupont C, Chouraqui JP de, Boissieu D, et al. [Dietetic treatment of cow's milk protein allergy]. Arch.Pediatr. 2011;18(1):79-94.
  7. Huang J, Frohlich J, and Ignaszewski AP. The impact of dietary changes and dietary supplements on lipid profile. Can.J.Cardiol. 2011;27(4):488-505.
  8. Iacovou M, Ralston RA, Muir J, et al. Dietary management of infantile colic: a systematic review. Matern.Child Health J. 2012;16(6):1319-1331.
  9. Koletzko S, Niggemann B, Arato A, et al. Diagnostic approach and management of cow's-milk protein allergy in infants and children: ESPGHAN GI Committee practical guidelines. J.Pediatr.Gastroenterol.Nutr. 2012;55(2):221-229.
  10. Leonard SA and Nowak-Wegrzyn A. Food protein-induced enterocolitis syndrome: an update on natural history and review of management. Ann.Allergy Asthma Immunol. 2011;107(2):95-101.
  11. Li L, Ying XJ, Sun TT, et al. Overview of methodological quality of systematic reviews about gastric cancer risk and protective factors. Asian Pac.J.Cancer Prev. 2012;13(5):2069-2079.
  12. Liu ZM, Chen YM, and Ho SC. Effects of soy intake on glycemic control: a meta-analysis of randomized controlled trials. Am.J.Clin.Nutr. 2011;93(5):1092-1101.
  13. Sherzai A, Heim LT, Boothby C, et al. Stroke, food groups, and dietary patterns: a systematic review. Nutr.Rev. 2012;70(8):423-435.
  14. Yang B, Chen Y, Xu T, et al. Systematic review and meta-analysis of soy products consumption in patients with type 2 diabetes mellitus. Asia Pac.J.Clin.Nutr. 2011;20(4):593-602.
  15. Yang G, Shu XO, Chow WH, et al. Soy food intake and risk of lung cancer: evidence from the Shanghai Women's Health Study and a meta-analysis. Am.J.Epidemiol. 11-15-2012;176(10):846-855.
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