- What other names is Soy known by?
- What is Soy?
- Is Soy effective?
- How does Soy work?
- Are there safety concerns?
- Are there any interactions with medications?
- Dosing considerations for Soy.
Soy is used for high cholesterol, high blood pressure, and preventing diseases of the heart and blood vessels. It is also used for type 2 diabetes, asthma, lung cancer, endometrial cancer, prostate cancer, and thyroid cancer, as well as preventing weak bones (osteoporosis), and slowing the progression of kidney disease.
Other uses include treating constipation and diarrhea, as well as decreasing protein in the urine of people with kidney disease, improving memory, and treating muscle soreness caused by exercise.
Women use soy for breast pain, preventing breast cancer, preventing hot flashes after breast cancer, menopausal symptoms, and premenstrual syndrome (PMS).
In foods, soy is used as a milk substitute in infant feeding formulas, and as an alternative to cow's milk. Soybeans are eaten boiled or roasted. Soy flour is used as an ingredient in foods, beverages, and condiments.
The active ingredients in soy are called isoflavones. A study of the quality of commercially available soy supplements suggests that less than 25% of products contain within 90% of labeled isoflavone content. Paying more for a product doesn't necessarily guarantee that the content shown on the label is accurate.
In women near or after menopause, soy seems to be able to relieve hot flashes, reduce the risk of osteoporosis (weak bones), and possibly lower blood pressure.
In men, there is some evidence that soy milk might reduce the risk of developing prostate cancer.
Soy does not seem to be able to relieve hot flashes in women with breast cancer who are receiving certain anti-cancer drugs, like tamoxifen (Nolvadex), that can cause hot flashes.
There isn't enough information to know if soy is effective for the other conditions people use it for, including preventing breast and endometrial cancer.
Possibly Effective for...
- Breast cancer. Eating a high-soy diet is linked to a slightly reduced risk of developing breast cancer. Researchers think early exposure to soy may be key. Asian women who eat a traditional diet high in soy seem to be less likely to develop breast cancer. This benefit continues even when Asian women move to western cultures, where soy is less likely to be a regular part of the diet. This suggests that exposure to soy early in life (i.e., before menopause) provides the most protection against breast cancer.
- Diabetes. Most evidence suggests that taking soy products reduces blood sugar levels in people with diabetes. One study suggests that eating a whole soy diet, not just the protein from soy, reduces blood sugar in people with and without diabetes. However, there is also some evidence that suggests that soy and soy protein don't affects blood sugar in people with diabetes.
- Kidney disease in people with diabetes. Soy isoflavones might help prevent or treat kidney disease in people with diabetes.
- Diarrhea. Feeding infants formula supplemented with soy fiber, alone or together with rehydration solution, seems to reduce the duration of diarrhea compared to cow's milk formula or rehydration solution alone. However, in some studies formula supplemented with soy was no more beneficial than cow's milk formula. In adults, early evidence suggests that taking soy fiber does not decrease the incidence of diarrhea.
- Trouble digesting the sugar galactose (galactosemia). Feeding a soy-based formula to infants who have galactosemia seems to be helpful.
- Trouble digesting the sugar lactose (hereditary lactase deficiency). Feeding a soy-based formula to infants who have hereditary lactase deficiency seems to be helpful.
- Trouble digesting the sugar lactose (lactose intolerance). Feeding a soy-based formula to infants who have lactose intolerance seems to be helpful.
- High cholesterol. Eating soy protein in place of other dietary protein or using soy fiber products seems to slightly reduce total cholesterol and "bad cholesterol" (low-density lipoprotein (LDL) cholesterol levels). However, not all evidence is positive. Some studies have shown no significant benefit of soy protein on cholesterol levels.
- Kidney disease. Taking soy protein by mouth seems to reduce protein in the urine in people with kidney disease.
- Menopausal symptoms. Eating soy protein seems to help hot flashes caused by menopause. However, it does not reduce other symptoms of menopause, such as vaginal dryness or itching. Also, soy does not seem to help hot flashes in women with breast cancer.
- Osteoporosis. Most evidence suggests that soy protein can increase bone mineral density (BMD) or slow BMD loss in women near or beyond menopause. Soy might also reduce the risk of fractures in some women. Soy does not seem to affect BMD in younger women.
Possibly Ineffective for...
- Colorectal cancer. Research suggests that taking soy protein does not reduce the progression of colorectal cancer.
- Muscle soreness caused by exercise. Taking soy isoflavone extract by mouth before exercising does not seem to prevent muscle soreness.
- Fibromyalgia. Drinking a soy protein shake containing soy isoflavones does not appear to improve physical function or symptoms of depression in people with fibromyalgia.
- Rheumatoid arthritis. Early evidence suggests that consuming a liquid diet containing soy protein (Top Up) does not improve pain, stiffness, or joint swelling in people with rheumatoid arthritis.
Insufficient Evidence to Rate Effectiveness for...
- Asthma. Early evidence suggests that people with asthma who eat soy foods have increased lung function.
- Heart disease. Some evidence suggests that postmenopausal women, but not men or pre-menopausal women, who eat a lot of soy in their diet might have a reduced risk of stroke, heart attack, or heart disease-related death.
- Mental function. There is conflicting evidence about the effect of soy on mental function. Some evidence suggests that eating more soy improves short-term and long-term memory. However, other research suggests that soy does not improve mental function, including memory.
- Crohn's disease. Research suggests that taking soy by mouth, along with standard treatment, increases bowel movements and improves symptoms, such as fatigue and body weight, in people with Crohn's disease.
- Endometrial cancer. Increasing soy intake might lower the risk of endometrial cancer. Endometrial cancer is less common in Japan, China, and other Asian countries where the usual diet is low in calories and high in soy and whole grain foods, vegetables, and fruits.
- High blood pressure. Some evidence suggests that eating soy protein might reduce systolic blood pressure (the top number in a blood pressure reading) by about 4 mmHg and diastolic blood pressure (the bottom number) by about 3 mmHg in people with pre-high blood pressure or mild high blood pressure. However, this is a relatively small reduction. Also, some research suggests that soy protein does not affect blood pressure.
- Colic in infants. Early research suggests that feeding infants a soy-based formula might reduce the duration of colic symptoms in infants who have trouble digesting cow's milk. However, other research suggests that feeding infants a soy-based formula does not improve crying in infants with colic.
- Lung cancer. Research suggests that men and women who consume a higher amount of dietary phytoestrogens, such as isoflavones from soy, are less likely to develop lung cancer than people who consume smaller amounts. Soy seems to prevent lung cancer more in men than women.
- Breast pain (mastalgia). Drinking soymilk might reduce monthly breast pain in some women.
- Memory. Some research suggests that a high-soy diet might slightly improve performance on memory tests.
- Metabolic syndrome (a condition that increases risk for diabetes and heart disease). Eating a soy nut diet appears to reduce blood sugar and decrease low-density lipoprotein (LDL or "bad") cholesterol in postmenopausal women with metabolic syndrome better than a soy-protein diet or a DASH diet.
- Migraines. Research suggests that taking a combination of soy isoflavones, dong quai, and black cohosh reduces the frequency of migraines associated with menstruation.
- Muscle strength. Research suggests that taking soy protein can increase lean tissue mass in people participating in resistance training. Other research suggests that consuming a specific soy protein product (Supro) can increase body mass and strength and reduce fatigue in athletes. However, other conflicting research shows that soy protein might not improve strength.
- Osteoarthritis. Early evidence shows that taking soy protein can improve motion, pain, and quality of life in people with osteoarthritis. However, taking milk-based protein also seems to have these effects.
- Sun-damaged skin. Evidence suggests that applying a soy moisturizer to the skin can improve skin color, fine lines, and texture.
- Premenstrual syndrome (PMS). Research suggests that taking soy protein for two menstrual cycles can reduce cramps and swelling associated with PMS.
- Prostate cancer. Research regarding the effect of soy on prostate cancer risk has been conflicting. Men who eat an Asian diet, which contains 10 times more soy than the average American diet, seem to have a lower risk of prostate cancer. However, it is unclear whether it is the soy in the diet of Asian men or other factors (such as genetic differences or differences in dietary fat) that protect against prostate cancer. Some research shows that taking soy protein can reduce the risk of prostate cancer in at-risk men. However, there is conflicting evidence about whether soy can affect the progression of prostate cancer.
- Thyroid cancer. Diets that include plenty of soy seem to be linked to a reduced risk of thyroid cancer.
- Weight loss. Some evidence suggests that eating soy protein along with a low-calorie diet can reduce weight in obese and overweight people more than a low-calorie diet alone. However, other evidence suggests that consuming soy-meal replacements while following a calorie-restricted diet does not improve weight loss in overweight people.
- Wrinkled skin. Evidence suggests that consuming soy isoflavones can improve the elasticity of skin and the appearance of fine wrinkles. >
- Other conditions.
Natural Medicines Comprehensive Database rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, and Insufficient Evidence to Rate (detailed description of each of the ratings).
Next: How does Soy work?
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