Natural Products

Soy

Glycine max

Efficacy

• Indications with proven efficacy:
  None
• Indications with possible, but poorly documented efficacy - the use of this product cannot be recommended:
  Breast cancer prevention
  Hot flashes related to menopause
  Hyperlipidemia
  Hypertension
  Osteoporosis
  Prostate cancer prevention
  Proteinuria
• Also used for these other indications, but with no proof of efficacy:
  Cyclical breast pain

Security

• Risk of Drug Interactions: Low
• Adverse Effects: Not Frequent

What is it?

Soy is a legume cultivated in most parts of the world. In fact, it is one of the most cultivated plants in the world. Soy is an important source of plant protein, and plays a more and more important role in the human diet. Tofu, tempeh, soy milk and beans are some of the main dietary sources of soy. The protein content of various soy products can considerably vary.

Soy contains several active compounds: choline, lecithin and isoflavones. Soy proteins should be used preferably, because soy extracts do not appear to be very effective. One gram of soy protein contains 1 to 3 mg of isoflavones.

Warning

In 2004, Canada adopted new regulations that control the manufacturing, packaging, labeling and importing of natural health products. The new regulations also include an adverse reaction reporting system. Products that conform to the regulation's criteria are identified with a natural product number (NPN) or homeopathic medicine number (DIN-HM) and can be legally sold in Canada. This number indicates that the product meets specific criteria for safety and purity, not that it is effective for any indication.

Medicinal plants content varies naturally from plant to plant – just as fruits from the same package may vary in taste and texture. There is no standard to measure the active content of each plant. Thus, efficacy of natural products should be expected to vary from brand to brand as well as from bottle to bottle of the same brand.

For more information about the Natural Health Products Regulations, or to check if a product has been assessed, visit the Health Canada website at http://www.hc-sc.gc.ca/dhp-mps/prodnatur/index-eng.php.

Does it work?

Soy protein is used for indications where it may be of some benefit:

• Hyperlipidemia:
  Replacing animal protein by soy protein in one's diet may lower total cholesterol, "bad" cholesterol and triglyceride levels in people with hypercholesterolemia. A regular daily intake of 20 to 50 grams of soy protein is recommended.
• Breast cancer prevention:
  Eating soy protein during childhood and teenage years may lower the risk of breast cancer later in life.
• Hot flashes related to menopause:
  Eating 20 to 60 g of soy proteins (providing 34 to 76 mg of isoflavones) daily may reduce the frequency and intensity of hot flashes related to menopause.
• Hypertension:
  Soy protein is used to lower blood pressure in perimenopausal women.
• Osteoporosis:
  Daily ingestion of 40 g of isoflavone-rich (2-2,5 mg/g) soy protein may lower the risk of osteoporosis in menopausal women.
• Prostate cancer prevention:
  Men who drink large amounts of soymilk appear to less at risk of prostate cancer. The recommended amount is two glasses of soymilk daily.
• Proteinuria:
  A diet rich in soy protein may slow the progression of chronic renal insufficiency in people with proteinuria. A soy protein diet limited to 700-800 mg/kg daily is recommended.

There is insufficient reliable information to conclude that this plant is effective in any other indication.

Is it safe?

• Soy sometimes causes constipation, bloating and nausea. People with allergic rhinitis, asthma, and cow milk allergies are more at risk of being allergic to soy. Inhaling soy dust can also trigger an asthma attack. In addition, a soy-rich diet can increase the risk of kidney stones.
• Dietary amounts of soy are safe during pregnancy and while breast-feeding. However, pregnant women should not eat large amounts of soy proteins.
• Soymilk is contraindicated in children with cystic fibrosis.
• Soy can reduce the effects of tamoxifen and hormone replacement therapy. It can however increase the effects of oral anticoagulant such as Coumadin^TM. The risk of bleeding could increase. Taking soy within three hours (before or after) of taking thyroid drugs is also unadvisable because absorption would be reduced.

Clinical notes

• Seventy percent (70%) of the soy produced in the United-States was genetically modified.

References

1. Natural Medicines Comprehensive Database, 3rd edition, Therapeutic Research Faculty, 2007
2. Passeportsanté.net. Protéines et isoflavones de soya. http://www.passeportsante.net
3. Kotecha N. and Lockwood B. Soy - relieving the symptoms of menopause and fighting osteoporosis. The Pharmaceutical Journal, 15 October 2005