Soy

Botanicals

18/Description

About

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.

How it works

Soy contains "isoflavones" which are changed in the body to "phytoestrogens." Phytoestrogen molecules are similar in chemical structure to the hormone estrogen. In some cases, these phytoestrogens can mimic the effects of estrogen. In other cases, these phytoestrogens can block the effects of estrogen.

Effectiveness

Possibly Effective
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.

Concerns

Likely safe

Consuming foods containing soy protein or taking soy protein products is LIKELY SAFE

Possibly safe

Taking dietary supplements with soy extracts is POSSIBLY SAFE when used short-term (up to 6 months). Soy can cause some mild stomach and intestinal side effects such as constipation, bloating, and nausea. It can also cause allergic reactions involving rash and itching in some people. Some people might experience tiredness. Soy might also affect thyroid function. However, this seems to occur primarily in people who are iodine deficient

Possibly unsafe

Long-term use of high doses of soy extract is POSSIBLY UNSAFE. There is some concern that taking high doses might cause abnormal tissue growth in the uterus. However, eating large amounts of soy does not seem to have this effect.

18/Warnings

Warnings

Pregnancy and breast-feeding: Soy protein isLIKELY SAFEto be used duringpregnancyand breast-feeding when consumed in amounts normally found infood. However, soy may bePOSSIBLY UNSAFEwhen used during pregnancy in medicinal amounts. Higher doses during pregnancy might harmdevelopmentof the baby. Not enough is known about the safety of higher doses during breast-feeding. Stay on the safe side and avoid larger doses.

Children: Soy is LIKELY SAFE for children when used in amounts commonly found in food or infant formula. Using soy formula does not seem to cause health or reproductive problems later in life. However, soymilk that is not designed for infants should not be used as a substitute for infant formula. Regular soymilk could lead to nutrient deficiencies.

Soy is POSSIBLY UNSAFE when used as an alternative to cow's milk in children who are allergic to cow's milk. Although soy protein-based infant formulas are often promoted for children with milk allergy, these children are often allergic to soy as well.

Don't give children soy in amounts larger than what is found in food or formula. Researchers don't know whether soy is safe for children at higher doses.

Hay fever (allergic rhinitis): People with hay fever are more likely to be allergic to soy hulls.

Asthma: People with asthma are more likely to be allergic to soy hulls. Avoid using soy products.

Breast cancer: The effects of soy in people with breast cancer are unclear. Some research finds that soy might "feed" certain breast cancers because it can act like estrogen. Other studies have found that soy seems to protect against breast cancer. The difference in effects might have something to do with the amount taken. Because there isn't enough reliable information about the effects of soy in women with breast cancer, a history of breast cancer, or a family history of breast cancer, it's best to avoid using soy until more is known.

Cystic fibrosis: Soymilk can interfere with the way children with cystic fibrosis process protein. Don't give these children soy products.

Diabetes: Soy might increase the risk of blood sugar levels becoming too low in people with diabetes who are taking medication to control blood sugar.

Endometrial cancer: Long-term use of concentrated soy isoflavone tablets might increase the occurrence of precancerous changes in the tissue lining the uterus. However, conflicting evidence exists. Use supplements containing soy isoflavones cautiously if you are at risk for endometrial cancer. Soy foods are likely safe.

Under-active thyroid (hypothyroidism): There is a concern that taking soy might make this condition worse.

Kidney stones: There is some concern that soy products might increase the risk of kidney stones because they contain large amounts of a group of chemicals called oxalates. Oxalates are the main ingredient in kidney stones. Another concern is that people with serious kidney disease aren't able to process some of the chemicals in soy. This could lead to dangerously high levels of these chemicals. If you have a history of kidney stones, avoid taking large amounts of soy.

Milk allergy: Children who are very allergic to cow's milk might also be sensitive to soy products. Use soy products with caution.

Kidney failure: Soy contains a chemical called phytoestrogens. Very high levels of phytoestrogens can be toxic. People with kidney failure who use soy products might be at risk for blood levels of phytoestrogens becoming too high. If you have kidney failure, avoid taking large amounts of soy.

Urinary bladder cancer: Soy products might increase the chance of getting bladder cancer. Avoid soy foods if you have bladder cancer or a high risk of getting it (family history of bladder cancer).

Interactions

Always consult with your doctor.
Moderate
Antibiotic drugs

Fermented soy products such as tofu and soy sauce contain tyramine. Tyramine is an amino acid that is involved in blood pressure regulation. Tyramine is broken down by monoamine oxidase. Some medications for depression (MAOIs) can decrease the breakdown of tyramine. Consuming more than 6 mg of tyramine while taking one of these medications can increase the risk of serious side effects such as blood pressure getting too high. The amount of tyramine in fermented soy products is usually small, often less than 0.6 mg per serving; however, there can be variation depending on the specific product used, storage conditions, and length of storage. Storing one brand of tofu for a week can increase tyramine content from 0.23 mg to 4.8 mg per serving. If you take one of these medications, avoid fermented soy products that contain high amounts of tyramine.Some of these medications include phenelzine (Nardil), tranylcypromine (Parnate), and others.Antibiotics are used to reduce harmful bacteria in the body. Antibiotics can also reduce friendly bacteria in the intestines. Friendly bacteria in the intestines seem to help increase the effectiveness of soy. By reducing the number of bacteria in intestines, antibiotics might decrease the effectiveness of soy. But it is too soon to know if this interaction is a big concern.

Progesterone

Large amounts of soy might have some of the same effects as estrogen. But soy isn't as strong as estrogen pills. Taking soy along with estrogen pills might decrease the effects of estrogen pills.Some estrogen pills include conjugated equine estrogens (Premarin), ethinyl estradiol, estradiol, and others.Levothyroxine is used for low thyroid function. Soy can decrease how much levothyroxine your body absorbs. Taking soy along with levothyroxine might decrease the effectiveness of levothyroxine. The dose of levothyroxine may need to be adjusted if soy is being used regularly, such as in soy-based formulas. If soy is used occasionally, levothyroxine and soy should be taken at least 4 hours apart.Some brands that contain levothyroxine include Armour Thyroid, Eltroxin, Estre, Euthyrox, Levo-T, Levothroid, Levoxyl, Synthroid, Unithroid, and others.Soy can decrease blood sugar levels. Diabetes medications are also used to lower blood sugar. Taking soy along with diabetes medications might cause your blood sugar to be too low. Monitor your blood sugar closely. The dose of your diabetes medication might need to be changed.Some medications used for diabetes include glimepiride (Amaryl), glyburide (DiaBeta, Glynase PresTab, Micronase), insulin, metformin (Glucophage), pioglitazone (Actos), rosiglitazone (Avandia), and others.Soy protein might reduce blood pressure. Using soy with drugs that lower blood pressure might increase the effects of these drugs and may lower blood pressure too much.Some medications for high blood pressure include captopril (Capoten), enalapril (Vasotec), losartan (Cozaar), valsartan (Diovan), diltiazem (Cardizem), amlodipine (Norvasc), hydrochlorothiazide (HydroDiuril), furosemide (Lasix), and many others.Bone loss might occur in women with osteoporosis who combine progesterone with soymilk containing isoflavones.

Tamoxifen (Nolvadex)

Some types of cancer are affected by hormones in the body. Estrogen-sensitive cancers are cancers that are affected by estrogen levels in the body. Tamoxifen (Nolvadex) is used to help treat and prevent these types of cancer. Soy seems to also affect estrogen levels in the body. By affecting estrogen in the body, soy might decrease the effectiveness of tamoxifen (Nolvadex). Do not take soy if you are taking tamoxifen (Nolvadex).

Warfarin (Coumadin)

Warfarin (Coumadin) is used to slow blood clotting. Soy has been reported to decrease the effectiveness of warfarin (Coumadin). Decreasing the effectiveness of warfarin (Coumadin) might increase the risk of clotting. It is unclear why this interaction might occur. Be sure to have your blood checked regularly. The dose of your warfarin (Coumadin) might need to be changed.

Water pills (Diuretic drugs)

Early research suggests that soy can increase urine production. The effects seem to be similar to those of "water pills." Taking soy along with "water pills" might increase the risk for side effects.

The information provided on this page is for reference purposes and is not meant to be used as a medical advice, diagnosis or treatment. Always consult with a medical professional. The content on this page has been provided with thanks by RxList.com