Soy (Glycine max)


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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 provider.

Dietary source of protein
Soy products, such as tofu, are high in protein and are an acceptable source of dietary protein. 		A
High cholesterol
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) is altered in some, but not all, studies. Some scientists have proposed that specific components of soybean, such as the isoflavones genistein and daidzein, may be responsible for the cholesterol-lowering properties of soy. However, this has not been clearly demonstrated in research and remains controversial. It is not known if products containing isolated soy isoflavones have the same effects as regular dietary intake of soy protein. Dietary soy protein has not been proven to affect long-term cardiovascular outcomes, such as heart attack or stroke. 		A
Diarrhea (acute) in infants and young children
Numerous studies report that infants and young children (2-36 months old) with diarrhea who are fed soy formulas experience fewer daily bowel movements and fewer days of diarrhea. This research suggests that soy has 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. 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
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 recommendations can be made. 		C
Bowel/intestinal disorders
The effect of soy on erosive-ulcer lesions of the alimentary tract has been examined in limited study. Overall, the effects of soy products appear beneficial. Further study is required before recommendations can be made. 		C
Cancer (prevention and treatment)
Several large population studies have asked people about their eating habits and reported that higher soy intake (such as dietary tofu) is associated with a decreased risk of developing various types of cancers, including breast, prostate, and colon cancer. However, other research suggests that soy does not have this effect. Until better research is available, it remains unclear if dietary soy or soy isoflavone supplements increase or decrease the risk of these cancers. 		C
Cardiovascular disease
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 the risk of heart problems. 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. In women with suspected cardiac ischemia, high levels of the soy isoflavone genistein have been associated with blood vessel problems. Further investigation is needed before a strong recommendation can be made. 		C
Cognitive function
It is unclear if soy isoflavone supplementation in postmenopausal women can improve cognitive function. Results from studies are mixed. 		C
Crohn's disease
Due to limited human research, there is not enough evidence to recommend for or against the use of soy as a way to prevent Crohn's disease. Further research is needed before a recommendation can be made. 		C
Cyclical breast pain
It has been theorized that the "phytoestrogens" (plant-based compounds with weak estrogen-like properties) in soy may be beneficial to premenopausal women with cyclical breast pain. However, due to limited human research, there is not enough evidence to recommend for or against the use of dietary soy protein as a therapy for this condition. 		C
Diabetes
Several small studies have examined the effects of soy products on blood sugar levels 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. 		C
Exercise performance enhancement
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 no protein but is unlikely to be superior to other sources of protein. Further research is required in this field. 		C
Gallstones (cholelithiasis)
Due to limited human research, 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 strong recommendation can be made. 		C
Gastrointestinal motility
In limited available studies, the addition of soy polysaccharide to non-regular diets increased the moisture content of stool and decreased the number of liquid stools. It is not clear if soy polysaccharide would be superior to other fiber sources in this regard. 		C
High blood pressure
There is limited human research on the effects of dietary soy on blood pressure. Some research suggests that substituting soy nuts for non-soy protein may help improve blood pressure. Further research is needed before a firm recommendation can be made. 		C
Infantile colic
There is currently a lack of scientific evidence to recommend for or against the use of soy formula for fussiness and gas in infants with cow's milk allergy over a partially hydrolyzed cow's milk protein formula. 		C
Inflammation
There is currently a lack of scientific evidence to recommend for or against the use of soy protein on inflammation associated with hemodialysis (removal of waste products from the blood). 		C
Iron deficiency anemia
There is currently a lack of sufficient evidence to recommend for or against the use of soy-based formula in the treatment of iron deficiency anemia in children. 		C
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 with their healthcare providers about the recommended amounts of dietary protein because soy is a high-protein food. 		C
Menopausal symptoms
Overall, evidence suggests that soy products containing isoflavones may help reduce menopausal symptoms, such as hot flashes. More study is needed to confirm this use. 		C
Menstrual migraine
A phytoestrogen combination may help prevent menstrual migraine attacks. Further research is needed before a strong recommendation can be made. 		C
Metabolic syndrome
Treatment with soy protein and soy nuts was evaluated in patients with metabolic syndrome and benefits were found in terms of plasma lipids in patients consuming soy nuts as part of the DASH (Dietary Approaches to Stop Hypertension) diet. Further research is required in this field in terms of soy protein supplementation. 		C
Obesity/weight reduction
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 strong recommendation can be made. 		C
Osteoarthritis
Osteoarthritis is a form of arthritis caused by the breakdown of cartilage. Early research suggests that intake of soy protein may be associated with reduced symptoms of osteoarthritis. 		C
Osteoporosis
It has been theorized that "phytoestrogens in soy" (such as isoflavones) may increase bone mineral density in post-menopausal women and reduce the risk of fractures. However, more research is needed before a conclusion can be made. 		C
Quality of life
The effect of soy on quality of life has been investigated in limited study. Further study is required before recommendations can be made. 		C
Rheumatoid arthritis
There is currently insufficient evidence to recommend for or against the use of soy as a treatment for rheumatoid arthritis. 		C
Skin aging
It is unclear if aglycones, a form of soy isoflavone, can improve aged skin in middle-aged women when it is taken by mouth. More research is needed. 		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 available study investigated whether soy protein could be used to increase ambulation performance in patients with incomplete spinal cord injury. There is currently not enough evidence to recommend for or against the use of soy as a treatment for increased endurance in individuals with spinal cord injury. 		C
Thyroid disorders
Early research suggests that soy supplements do not affect thyroid function. More research is needed. 		C
Tuberculosis
It has been suggested that soy may be beneficial for tuberculosis when taken with standard medications. According to early research, soy may improve the process of detoxification, have positive effects on the liver, reduce cell damage, and decrease inflammation. Therefore, soy supplements may allow patients to safely take higher doses of antimicrobial drugs that are used to treat tuberculosis. 		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 proteins (broken down). Further research is required in this field. 		C

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)

Grading rationale

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 healthcare provider.

Alzheimer's disease, anorexia, anti-aging, antifungal, arthritis, atherosclerosis (hardening of the arteries), attention deficit hyperactivity disorder (ADHD), benign prostate hyperplasia, bone density, bone fractures, breast enlargement, colitis, constipation, cystic fibrosis, diabetic neuropathy, fall prevention, fever, growth, headache, hepatitis (chronic), immune function, improving health outcomes (general), infertility, insect repellant, kwashiorkor, malnutrition, melasma (skin discoloration), memory enhancement, nosebleed (chronic), osteosarcoma, polycystic ovary syndrome, respiratory problems (cough, phlegm), skin conditions, thrombosis (blood clotting), vaginitis, vasoregulator, wound healing.

Dosing Related terms
NS_patient-soy Portions of this document last updated: Sept. 1, 2012

THIS EVIDENCE-BASED MONOGRAPH WAS PREPARED BY
THE NATURAL STANDARD RESEARCH COLLABORATION
(www.naturalstandard.com)

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