Soy (Glycine max)

Soy: Medical Uses

Soy is used for high cholesterol, diabetes mellitus, and menopausal symptoms and is also used for its anticancer effects and prevention of osteoporosis.

Historical Uses

In China, soy is valued highly and has been called one of the five sacred grains.


Soy is a subtropical plant that is now cultivated in temperate regions. The plant grows from 1 to 5 feet tall.

Part Used

• Seed (soybean)

Major Chemical Compounds

• Genistein, a major isoflavone in soy and a weak estrogen

• Daidzein, another isoflavone

Soy: Clinical Uses

Soy is used to treat high cholesterol (, diabetes mellitus, and menopausal symptoms and is also used for its anticancer effects and prevention of osteoporosis. Labels approved by the Food and Drug Administration state that soy may help lower cholesterol levels and reduce the risk of heart disease. Soy is approved by the German Commission E for mild hypercholesterolemia.

Soy products containing isoflavones may provide a viable alternative to hormones for maintaining bone density and protecting against cardiovascular diseases, especially for postmenopausal women who choose to not take hormone replacement therapy. Japanese people consume an average of 7 to 10 grams of soy protein daily and about 30 to 50 mg of isoflavones daily. Soy may have implications for breast cancer prevention.

Mechanism of Action

The mechanism of action is unknown at this time, although we know that soy may have anticancer properties. It may protect against breast cancer by interfering with estradiol (acting as an anti-estrogen). Phytoestrogens, like isoflavones, have both estrogenic and anti-estrogenic effects. If phytoestrogens compete with natural estrogen to bind with body’s estrogen receptors, they may decrease the receptors’ ability to pick up estradiol in premenopausal women. In post-menopausal women, who have little of their own estradiol, phytoestrogens could have a small estrogenic effect.

Isofiavones enhance bone formation. The mechanism of action of isofiavones is different from that of human estrogen. The degree to which soy consumption decreases low-density lipoprotein levels is similar to that seen with hormone replacement therapy.

Soy: Dosage

It is estimated that 200 mg of isofiavones are equal to about 0.3 mg of Premarin. The average dosage of Premarin is 0.625 mg daily.

Isofiavones or soy protein: 40 to 100 mg of isofiavones or 30 to 50 grams of soy protein daily. Cholesterol-lowering benefits may occur with 25 grams (or 2 to 4 servings of soy foods) daily. For relief of hot flashes and maintenance of bone density, 40 to 60 grams daily maybe needed (Natural Medicines, 2000). Do not exceed 100 mg per day of isoflavone supplements because the effect of large supplemental doses over long periods is unknown. For soy to be absorbed properly, healthy bacteria (acidophilus) are needed in the digestive tract.

Food sources: The more processed the soybean, the lower its nutritional value. Soybeans contain the most isofiavones (and about 80 mg of calcium per ½ cup), whereas soy oil and soy sauce have virtually none.

Soy milk: Soy milk contains the same amount of protein as cow’s milk, one-third the fat of cow’s milk, fewer calories than cow’s milk, no cholesterol, many B vitamins, and 15 times as much iron, although cow’s milk is higher in calcium. It can be drunk by the glass and used in Recipes as a substitute for cow’s milk. Soy milk contains about 10 grams of protein, 20 mg of isofiavones, and 250 to 300 mg of calcium (fortified) per cup. It is made by grinding soybeans, mixing them with water, boiling and filtering the liquid, and sweetening it with vanilla, chocolate, or carob.

Tofu: Tofu is curdled soy milk that is drained and pressed. Its firmness depends on the amount of whey it contains. Extra-firm tofu has the most protein and is great in stir-fry dishes. Firm tofu can be used in lasagnas. Soft tofu can be used for desserts or puddings. Tofu contains 15 grams of protein, 40 mg of isofiavones, and about 130 mg of calcium per ½ cup.

Textured soy protein: This form of soy is similar to ground beef or turkey and can be used in chili, lasagna, or tacos. It contains about 22 grams of protein and 170 mg of calcium per cup.

Tempeh: This form of soy is like a soybean cake. It can be baked, grilled, or microwaved. It is high in fiber and contains no cholesterol. It contains about 15 grams of protein, 60 mg of isofiavones, and 77 mg of calcium per ½ cup.

Soy powder: This form of soy is high in protein, B vitamins, and iron. It can be added to fruit shakes or milkshakes.

Side Effects

Soy, especially soy protein powder, may cause bloating, nausea, and constipation.


• Soy is contraindicated in patients who are allergic to it.

• Soybeans should not be eaten raw.

Herb-Drug Interactions

None are known.

Pregnancy and Breast-Feeding

No restrictions are known if soy is consumed as a food. Isonavone supplements are not recommended during pregnancy.

Pediatric Patients

Isonavone supplements are not recommended in children().

Summary of Studies

The National Institutes of Health are currently studying soy isoflavones and their effects in preventing breast, prostate, colon, and lung cancer.

Potter et al. (1998). This double-blind study of postmenopausal women looked at the effects of soy isoflavones on bone density over a 6-month period. One group of women consumed 40 grams of non-soy protein daily; the other consumed soy-based protein with high levels of isoflavones (2.25 mg of isoflavones per gram of protein). Results: Spinal bone density increased in the group that consumed high levels of isoflavones.

Anderson et al. (1995). This meta-analysis included 38 controlled trials of soy and serum lipids. Results: Soy protein at about 47 grams daily decreased total cholesterol levels by 9.3 percent, low-density lipoprotein levels by 12.9 percent, and triglyceride levels by 10.5 percent.

Ho et al. (2001). In this longitudinal study, 132 women aged 30 to 40 years were followed for 3 years. Soy intake had a significant effect on the maintenance of spinal bone mineral density in this age group.

Soy: Warnings

  • • Don’t eat raw soybeans.
  • • Soy may cause allergic reactions.
  • • Soy, especially soy protein powder, may cause bloating, nausea, and constipation.
  • • No restrictions are known for pregnant and breast-feeding women if soy is consumed as a food.
  • • Isofiavone supplements aren’t recommended for children or pregnant women.