Report on Soy Side Effects and Usage


Natural health supplements sometimes have unexpected side effects or interactions with medication that can lead to adverse reactions that are sometimes life threatening. The following is a list of cautions that you should be aware of before using Soy (Glycine max). These are referred to as drug/herb interactions.

Warning 1 – Contraindications: Children with cystic fibrosis. Soymilk can interfere with the digestion process of protein in children with cystic fibrosis.

Warning 2 – Allergic rhinitis (Hay fever): People with hay fever are more likely to be allergic to soy hulls and soy products.

Warning 3 – Asthma: People with asthma are more likely to be allergic to soy hulls and soy products.

Warning 4 – Birth control pills: Three websites (,, and claim that, “Taking soy along with estrogen pills might decrease the effects of estrogen pills.” This may be a concern if you are taking one of the following birth control pills; Yaz (also known as Yasmin or Ocella), Tri-Sprintec, Alesse, Desogestrel, Ortho Novum, Ortho Evra Patch, Nortrel 1/35, Ortho Tri-Cyclen, and many others. NuvaRing also contains estrogen.

Warning 5 – Bladder cancer: Soy products might increase the chance of getting urinary bladder cancer. Avoid soy products if you have bladder cancer have a family history of bladder cancer.

Warning 6 – Breast cancer: Although some studies have found that soy seems to protect against getting breast cancer, other research finds that in those who have breast cancer, soy might actually “feed” the cancer because it can act like estrogen. Until more is known about how soy products affect cancer and that risk, it is best to avoid soy products in women with breast cancer, a history of breast cancer, and those with a family history of breast cancer.

Warning 7 – Endometrial cancer: Long-term use of concentrated soy isoflavone tablets might increase the occurrence of precancerous changes in tissues lining the uterus. Those with endometrial cancer are encouraged to avoid the use of concentrated soy isoflavone supplements.

Warning 8 – Hypothyroidism (under-active thyroid): There is a concern that taking soy might make this condition worse. The isoflavones in soy products can depress thyroid function and cause goiters in otherwise healthy children and adults.

Warning 9 – Kidney disease: Soy products contain large amounts of a group of chemicals called oxalates, which are the main ingredient in kidney stones. There is a concern that using soy products might increase the risk of kidney stones. Another concern is that people with serious kidney disease may not be able to process some of the chemicals in soy products. This could lead to a build up of dangerously high levels of these chemicals in the body. If you have kidney disease or a family history of kidney stones, avoid taking large amounts of soy.

Warning 10 – Migraine headaches: Tyramine has also been associated with migraine headaches. Migraine sufferers often find that a tyramine-free diet makes them headache free.

Warning 11 – Thyroid hormones: Using soy with thyroid hormones may interfere with the body’s ability to absorb the thyroid hormones. Experts recommend avoiding concurrent use.

Researchers at Cornell University Medical College said that children who got soy formula were more likely to develop thyroid disease and that twice as many diabetic children had received soy formula in infancy as compared to non-diabetic children. In fact, in other countries such as Switzerland, England, Australia and New Zealand, public health officials recommend highly restricted medically monitored use of soy for babies and for pregnant women. Dr. Mercola – “Soy formula is one of the worst foods that you could feed your child. Not only does it have profoundly adverse hormonal effects as discussed above, but it also has over 1000% more aluminum than conventional milk based formulas.”

Warning 12 – Long-term use: The use of high doses of soy dietary supplements over long periods of time is still controversial. There is concern that taking high doses might cause the growth of abnormal tissue in the uterus.

Warning 13 – Medications for depression (MAOIs): Fermented soy products such as tofu and soy sauce contain tyramine, an amino acid that is involved in blood pressure regulation. Some medications for depression (MAOIs) can decrease the breakdown of tyramine. Consuming more than 6 mg of tyramine while taking phenelzine (Nardil), tranylcypromine (Parnate), and others, can increase the risk of serious side effects such as high blood pressure and migraine headaches.

The amount of tyramine in fermented soy products is usually small but can increase over time. Storing one brand of tofu for a week can increase tyramine content from 0.23 mg to 4.8 mg per serving. Experts recommend that you avoid fermented soy products that contain high amounts of tyramine if you take MAOIs.

Warning 14 – Soymilk 1: Although soy-based infant formulas are often promoted for children who are allergic to cow’s milk, these children are often also allergic to soymilk.

Warning 15 – Soymilk 2: Soymilk that is not designed for infants should not be used as a substitute for infant formula. Using regular soymilk for infants could lead to nutrient deficiencies.

Warning 16 – Tamoxifen (Nolvadex): Some types of cancer are affected by hormone levels in the body and are said to be estrogen-sensitive. Tamoxifen (Nolvadex) is used to prevent and help treat these types of cancer. Soy seems to affect estrogen levels in the body, which might decrease the effectiveness of tamoxifen (Nolvadex). Experts recommend avoiding concurrent use of tamoxifen (Nolvadex) with soy products and soy supplements.

Warning 17 – Warfarin (Coumadin): Warfarin is used to slow blood clotting. Soy has been reported to decrease the effectiveness of warfarin. Soy contain hemagglutinin, a clot promoting substance that causes red blood cells to clump together. These clustered blood cells are unable to properly absorb oxygen for distribution to the body’s tissues. Decreasing the effectiveness of warfarin might increase the risk of clotting. Your dosage of warfarin might need to be changed if you start using soy products.

Warning 18 – Fertility: Researchers from the Harvard School of Public Health presented evidence at the 63rd annual meeting of the American Society for Reproductive Medicine showing that soy phytoestrogens can seriously lower a man’s sperm count. Dr. Chavarro and colleagues studied 100 men whose partners were having trouble getting pregnant. Semen analyses showed that the men with the highest levels of soy food intake-approximately a half serving per day-had 41 million sperm per milliliter fewer than men who did not consume any soy products.

Soy if often advertised as a natural health product however, soy protein is a highly processed food. Research to date suggests that soy may be beneficial for the following conditions.

  • Breast cancer risk. One study found that Asian women who eat a diet high in soy seem to be less likely to develop breast cancer. This benefit continued even when Asian women move to western cultures where soy is less likely to be a regular part of their diet. This suggests that exposure to soy early in life (i.e., before menopause) may provide some protection against breast cancer. (See other herbs for menopause)
  • High cholesterol. Eating soy protein seems to slightly reduce the “bad cholesterol” or low-density lipoprotein (LDL). However, some studies show no significant benefit.
  • Hot flashes caused by menopause. Note that this does benefit is not seen in women with breast cancer.
  • Osteoporosis (weak bones), especially in women who have passed menopause. Most evidence suggests that soy protein increases bone mineral density (BMD), or slow the loss of BMD in women near or beyond menopause. Note that this benefit is not seen in younger women.
  • Preventing and treating diabetic nerve problems.
  • Providing nutrition to infants who can’t digest milk sugars (controversial).
  • Reducing protein in the urine of people with kidney disease.
  • Reducing the duration of diarrhea in infants.
  • Treating diabetes type 2.
  • Treating infants who have trouble digesting lactose (galactosemia, hereditary lactose deficiency, lactose intolerance) (controversial).

In addition, those promoting soy products sometimes make claims that are not yet backed up by research. Those claims include:

  • Aid weight loss
  • Improve memory
  • Lower high blood pressure
  • Reduce breast pain
  • Reduce the risk of heart disease
  • Reduce the symptoms of Asthma
  • Reduce the symptoms of premenstrual syndrome (PMS)
  • Preventing cancer (Endometrial, Lung cancer, Prostate cancer)

Side Effects of soy products

According to those who promote soy products, for individuals who are not allergic to soy, no serious short-term or long-term side effects have been reported from eating soy foods. However, the following side effects of using soy have been reported:

  1. Blurred vision
  2. Fatigue
  3. Minor bloating
  4. Minor stomach cramps
  5. Those who have difficulty digesting soy may find themselves constantly exhausted but at the same time unable to sleep.

Other side effects may also occur when using soy products. (See form below)

As with any herb, a serious allergic reaction is possible. Seek immediate medical attention if you notice any symptoms of a serious allergic reaction. These may include a rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, or trouble breathing.

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For questions and answers about the side effects of herbs see the Herb Forum

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