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Soy

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What other names is Soy known by?

Cosse de Soja, Cosse de Soya, Daidzein, Daidzéine, Dolichos soja, Edamame, Estrogène Végétal, Fermented Soy, Fève de Soja, Fève de Soya, Fibre de Soja, Fibre de Soya, Frijol de Soya, Genestein, Genistein, Génistéine, Glycine gracilis, Glycine hispida, Glycine max, Glycine soja, Haba Soya, Haricot de Soja, Haricot de Soya, Hydrolyzed Soy Protein, Isoflavone, Isoflavone de Soja, Isoflavone de Soya, Isolated Soy Protein, Isolated Soybean Protein, Lait de Soja, Lait de Soya, Legume, Miso, Natto, Phaseolus max, Phytoestrogen, Phyto-œstrogène, Plant Estrogen, Protéine de Haricot de Soja Isolée, Protéine de Haricot de Soya Isolée, Protéine de Soja, Protéine de Soya, Protéine de Soja Isolée, Protéine de Soya Isolée, Shoyu, Soja, Soja hispida, Soja max, Sojabohne, Soy Bean, Soy Fiber, Soy Germ, Soy Isoflavone, Soy Isoflavones, Soy Milk, Soy Protein, Soy Protein Isolate, Soya, Soya Bean, Soja Fermenté, Soya Fermenté, Soybean, Soybean Curd, Soybean Isoflavone, Soybean Isoflavones, Tempeh, Texturized Vegetable Protein, Tofu, Touchi.

What is Soy?

Soy comes from soybeans. The beans can be processed into soy protein, which is a powder; soymilk, which is a beverage that may or may not be fortified with extra calcium from the soybeans; or soy fiber, which contains some of the fibrous parts of the bean.

Soy is taken by mouth for high cholesterol, high blood pressure, and preventing diseases of the heart and blood vessels. It is also used for type 2 diabetes and kidney disease associated with diabetes, asthma, as well as preventing weak bones (osteoporosis), preventing joint pain and stiffness in people with arthritis, and slowing the progression of kidney disease. Soy is also taken by mouth to prevent different kinds of cancer.

Soy is also taken by mouth for treating constipation, diarrhea, Crohn's disease, hepatitis C, metabolic syndrome, fibromyalgia, weight loss, enlarged prostate, as well as decreasing protein in the urine of people with kidney disease, improving memory and mental function, improving muscle strength, and treating muscle soreness caused by exercise.

Women take soy by mouth for breast pain, preventing hot flashes after breast cancer, menopausal symptoms, premenstrual syndrome (PMS), and migraine headaches during menstruation.

Soy is used as a milk substitute in infant feeding formulas, and as an alternative to cow's milk. It is fed to infants who are unable to process the sugar galactose, who are lactose intolerance, who have a condition called hereditary lactase deficiency, or who have infant colic.

Soy is applied to the skin to improve photo-aged skin or wrinkled skin.

Soy is applied inside the vagina to treat vaginal swelling due to decreased lubrication and thinning vaginal tissue (vaginal atrophy).

In foods, 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.

Is Soy effective?

Soy can reduce cholesterol when used in combination with a low-fat diet.

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 in some women. Asian women who eat a high-soy diet seem to have a lower risk of breast cancer than those who eat less soy. But most research shows no benefit in Western-culture women. It's possible that women of Western culture do not eat enough soy to see any benefit. The effects of soy on breast cancer risk also seem to vary depending on a woman's age and menopausal status. Women who eat a high-soy diet during adolescence seem to have a reduced risk of breast cancer. This suggests that early exposure to soy might protect against breast cancer later in life. In women already diagnosed with breast cancer, eating a high soy diet is linked to a reduced risk of breast cancer recurrence. But there is no reliable evidence that taking a soy isoflavones supplement reduces breast cancer growth.
  • Diabetes. Most evidence suggests that consuming soy products reduces blood sugar levels in people with diabetes. However, not all research shows a benefit. In general, dietary soy, soy fiber, and fermented soy seem to lower blood glucose, while processed soy products, such as isolated soy protein, may not work.
  • Kidney disease in people with diabetes. Research shows that eating soy protein in place of animal protein as part of the diet might help prevent or treat kidney disease in people with diabetes. But some early research shows that drinking soy milk doesn't help.
  • 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.
  • 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). Soy protein that contains higher amounts of an ingredient called isoflavones might work better than soy protein with little or no isoflavones. Also, soy might work better in people with high cholesterol that is more severe. Supplements containing purified soy isoflavones don't seem to work. Soy doesn't seem to lower triglycerides. Also, most research shows that soy doesn't increase "good cholesterol" (high-density lipoprotein (HDL) cholesterol).
  • Kidney disease. Taking soy protein by mouth seems to reduce protein in the urine in people with kidney disease. It also seems to reduce levels of certain nutrients and waste products, such as phosphorus and creatinine. These molecules can build up in the blood of people with long-term kidney disease.
  • Trouble digesting the sugar lactose (lactose intolerance). Feeding a soy-based formula to infants who have lactose intolerance seems to be helpful.
  • Menopausal symptoms. Eating soy protein or taking concentrated soy isoflavone extract seems to help hot flashes caused by menopause in some people. Taking soy products providing 100-200 mg of isoflavones in two or three divided doses per day might work better than taking lower or less frequent doses. In addition, using products that contain at least 15 mg of the specific isoflavone called genistein seem to work better than products that provide less genistein. Taking soy also seems to improve depression and body weight in women after menopause. It's unclear if soy reduces vaginal dryness or itching that is associated with menopause. Soy does not seem to help hot flashes in women with breast cancer.
  • Osteoporosis. Most evidence suggests that soy protein or soy extract can increase bone mineral density (BMD) or slow BMD loss in women near or beyond menopause. It appears that soy products need to contain at least 75 mg of an ingredient called isoflavones in order to work. Soy might also reduce the risk of fractures in some women. Soy does not seem to affect BMD in younger women.

Possibly Ineffective for...

  • Enlarged prostate (benign prostatic hyperplasia; BPH). Taking isoflavones isolated from soy doesn't seem to improve urination or other symptoms in people with an enlarged prostate.
  • Breast cancer-related hot flashes. Research shows that drinking a beverage containing soy or taking tablets containing soy extract does not reduce hot flashes in breast cancer survivors.
  • 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 research 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, but taking supplements containing an ingredient in soy called isoflavones doesn't appear to improve lung function or reduce asthma episodes in adults or children with poorly controlled asthma.
  • 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. Some soy formulations might work better than others.
  • 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. Eating more soy 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. However, some soy foods seem to lower the risk of endometrial cancer better than others. It's too early to know if soy supplements affect endometrial cancer risk.
  • Hepatitis C. Early research suggests that taking soy protein reduces the buildup of fat in the liver and lowers biomarkers linked with liver damage in patients with hepatitis C.
  • High blood pressure. Most research shows that eating soy protein can reduce systolic blood pressure (the top number in a blood pressure reading) by about 4-8 mmHg and diastolic blood pressure (the bottom number) by about 3-5 mmHg in people with pre-high blood pressure or slightly high blood pressure. However, this is a relatively small reduction.
  • 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, higher-quality research suggests that feeding infants a soy-based formula does not improve the duration of crying in infants with colic. Also, soy-based formula doesn't seem to improve crying compared to the drug dicyclomine.
  • Lung cancer. Men and women who consume a higher amount of dietary phytoestrogens, such as isoflavones from soy, seem to be less likely to develop lung cancer than people who consume smaller amounts. Soy seems to prevent lung cancer more in men than women. However, some research suggests that only non-smokers, not smokers, who eat soy have a lower risk of developing lung cancer.
  • 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 "bad"cholesterol (low-density lipoprotein (LDL) 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,conflicting research shows that soy protein might not improve strength.
  • Osteoarthritis. Early research 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. Research 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 is 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. Soy protein doesn't seem to reduce hot flashes in prostate cancer patients.
  • Thyroid cancer. Diets that include plenty of soy seem to be linked to a reduced risk of thyroid cancer.
  • Vaginal irritation due to decreased lubrication and thinning vaginal tissue (vaginal atrophy). Applying a vaginal gel containing soy extract seems to reduce vaginal dryness and pain and improve vaginal tissue in postmenopausal women with symptoms of vaginal atrophy.
  • Weight loss. Some research suggests that eating a soy-based, low-calorie diet can reduce weight in obese and overweight people more than a low-calorie diet alone. Eating foods containing soy fiber might also improve weight loss. Replacing meat protein with soy protein in the diet might improve weight loss in women, although conflicting data exists. Supplementing with soy-based meal replacements doesn't seem to improve weight loss or prevent weight gain. Soy protein doesn't seem to improve weight loss when eaten as part of a free-choice diet.
  • Wrinkled skin. Consuming soy isoflavones seems to improve the elasticity of skin and the appearance of fine wrinkles.
  • Other conditions.
More evidence is needed to rate soy for these uses.

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).


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