Uses & Effectiveness

Overview

Soy (Glycine max) comes from soybeans. The beans are a legume that come from China. They can be processed into soy protein, soy milk, or soy fiber.

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.

Soy is used for high cholesterol, high blood pressure, heart disease, diabetes, symptoms of menopause, and premenstrual syndrome (PMS). It is also used for many other conditions, but there is no good scientific evidence to support many of these uses.

Did you know that soy is a fantastic source of Vitamin K? Just one cup of soybeans contains 31.3 micrograms of Vitamin K, which plays a crucial role in blood clotting and bone health. Incorporating soy into your diet can help ensure you meet your daily Vitamin K requirements!

Side Effects

When taken by mouth: Soy is commonly consumed in foods. Dietary supplements containing soy extracts are possibly safe when used for 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, itching, and breathing problems in some people.

Interactions

Major Interaction

Do not take this combination

• Medications for depression (MAOIs) interacts with SOY

  Fermented soy products such as tofu and soy sauce contain tyramine. Tyramine is a naturally occurring chemical that is involved in blood pressure regulation. MAOIs can decrease how quickly the body breaks down tyramine. Consuming more than 6 mg of tyramine while taking one of these medications can increase the risk of serious side effects, such as very high blood pressure. If you take one of these medications, avoid fermented soy products that contain high amounts of tyramine.

  Some common MAOIs include phenelzine (Nardil), selegiline (Zelapar), and tranylcypromine (Parnate).

Moderate Interaction

Be cautious with this combination

• Estrogens interacts with SOY

  Large amounts of soy might have some of the same effects as estrogen. Taking soy along with estrogen pills might decrease the effects of estrogen pills.

• tamoxifen (Nolvadex) interacts with SOY

  tamoxifen affects the activity of estrogen in the body. Soy seems to also affect estrogen activity in the body. Taking soy with tamoxifen might change the effects of tamoxifen. Speak with a healthcare provider if you are taking tamoxifen.

• Warfarin (Coumadin) interacts with SOY

  Warfarin is used to slow blood clotting. Soy has been reported to decrease the effects of warfarin. This might increase the risk of clotting. Be sure to have your blood checked regularly. The dose of your warfarin might need to be changed.

• Medications for diabetes (Antidiabetes drugs) interacts with SOY

  Soy might lower blood sugar levels. Taking soy along with diabetes medications might cause blood sugar to drop too low. Monitor your blood sugar closely.

• Medications for high blood pressure (Antihypertensive drugs) interacts with SOY

  Soy might lower blood pressure. Taking soy along with medications that lower blood pressure might cause blood pressure to go too low. Monitor your blood pressure closely.

• levothyroxine (Synthroid, others) interacts with SOY

  levothyroxine is used for low thyroid function. Soy seems to decrease how much levothyroxine is absorbed by the body in infants, but not adults. This might decrease the effects of levothyroxine in infants. The dose of levothyroxine may need to be adjusted if soy is being used regularly, such as in soy-based formulas. Otherwise, take levothyroxine and soy at least 4 hours apart.

• Progesterone interacts with SOY

  Some research shows that taking soy milk along with progesterone might increase bone loss in females with osteoporosis.

• Water pills (Diuretic drugs) interacts with SOY

  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.

• Caffeine interacts with SOY

  Soy contains the chemical genistein. Genistein might slow down how quickly the body gets rid of caffeine. This might increase the effects of caffeine.

Minor Interaction

Be watchful with this combination

• Antibiotic drugs interacts with SOY

  Antibiotics are used to reduce harmful bacteria in the body. Antibiotics can also reduce friendly bacteria in the intestines. Friendly bacteria in the intestines help to convert soy to its active form. By reducing the number of bacteria, antibiotics might decrease the effects of soy. But it is too soon to know if this interaction is a big concern.

• Medications changed by the liver (Cytochrome P450 2C9 (CYP 2C9) substrates) interacts with SOY

  Some medications are changed and broken down by the liver. Soy might change how quickly the liver breaks down these medications. This could change the effects and side effects of these medications.

Special Precautions and Warnings

Pregnancy: Soy is commonly consumed in foods. However, soy is possibly unsafe when used in the larger amounts found in medicine when pregnant. Higher doses during pregnancy might harm development of the baby.

Breast-feeding: There isn’t enough reliable information to know if soy is safe to use in the larger amounts found in medicine when breast-feeding. Stay on the safe side and stick to food amounts.

Children: Soy is commonly consumed in foods. Giving infants soy formula doesn’t seem to cause health or reproductive problems later in life. But soy milk that is not designed for infants should not be used as a substitute for infant formula. Regular soy milk 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.

Breast cancer: The effects of soy in people with breast cancer are unclear. Because there isn’t enough reliable information about the effects of soy in females with breast cancer, a history of breast cancer, or a family history of breast cancer, it’s best to avoid using soy supplements until more is known.

Allergy to peanuts and related plants: Soy might cause serious allergic reactions in people who are allergic to peanuts and other members of the Fabaceae plant family.

Under-active thyroid (hypothyroidism): Some people with this condition also have low iodine levels. Taking soy might make this condition worse in people who have low iodine levels.

Kidney failure: Soy contains a chemical called phytoestrogens. People with kidney failure who use soy products might have blood levels of phytoestrogens become too high. If you have kidney failure, avoid taking large amounts of soy.

Kidney stones: Soy products might increase the risk of kidney stones. Soy products contain large amounts of chemicals called oxalates. Oxalates are the main ingredient in kidney stones. 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.

Bladder cancer: Soy products might increase the chance of getting bladder cancer. Avoid soy foods if you have bladder cancer or are at high risk of getting it.