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Fermented Soybeans (dan dou chi)

What is fermented soybeans? What is it used for?

Soybeans have a long use as a condiment and a type of medicine in Chinese culture; according to some sources, the cultivation of soybeans dates back more than 3,000 years.

For centuries, soybeans have been used as a source of protein and a healthy alternative to meat and fish. While salted black soybeans are used as a food source, tasteless black soybeans are used in herbal medicine. They are processed by being press-steamed, then fermented. Once the fermentation process is complete, the beans are dried in the sun and used raw. The soybeans must be fermented to be useful as an herbal medicine.

As a food source, soybeans provide a wealth of important nutrients, including protein, several amino acids and isoflavones. The isoflavones are believed to reduce the risk of some types of cancers, such as breast cancer and prostate cancer. Other compounds in soybeans help improve the immune system and can lower cholesterol levels in the blood. The German Commission E has approved the use of soy for lowering blood lipid levels.

In traditional Chinese medicine, fermented soybeans have pungent, sweet and slightly bitter properties, and are affiliated with the Lung and Stomach meridians. The main functions of fermented soybean are to release exterior hot and exterior cold caused by yin deficiency. They are often used to treat conditions such as restlessness and irritability, and help improve sleep patterns. Many practitioners use fermented soybeans to reduce fever and relieve stuffiness and congestion in the chest. Fermented soybeans are often used with other herbs such as cape jasmine and honeysuckle in larger formulas.

How much fermented soybean should I take?

The typical dosage of fermented soybean is between 10 and 15 grams, boiled in water as part of a decoction or tea. Some practitioners also offer soybean pastes and powders.

What forms of fermented soybean are available?

Whole fermented soybeans are widely available at Asian markets, specialty stores and some supermarkets. Some vendors also sell fermented soybean pastes and powders.

What can happen if I take too much fermented soybean? Are there any interactions I should be aware of? What precautions should I take?

Because fermented soybean is believed to inhibit lactation, it should not be taken by women who are pregnant or breastfeeding. Excessive intake of fermented soybeans may cause some minor side-effects such as stomach pain, loose stools and diarrhea. As always, make sure to consult with a licensed health care provider before taking fermented soybeans or any other herbal remedy or dietary supplement.


  • Blumenthal M, Busse WR, Goldberg A, et al. (eds.) The Complete German Commission E Monographs. Therapeutic Guide to Herbal Medicines. Boston: Integrative Medicine Communications, 1998, pp. 210-213.
  • Blumenthal M, Goldberg A, Brinckman J (eds.) Herbal Medicine. Expanded Commission E Monographs. Newton, MA: Integrative Medicine Communications, 2000, pp. 354-358.
  • Gruenwald J, Brendler T, Jaenicke C (eds.) PDR for Herbal Medicines. Montvale, NJ: Medical Economics Company, 2000, pp. 707-708.
  • Iwai K, Nakaya N, Kawasaki Y, Matsue H: Antioxidative functions of natto, a kind of fermented soybeans: Effect on LDL oxidation and lipid metabolism in cholesterol-fed rats. Journal of Agriculture and Food Chemistry 2002;50:3597-3601
  • Tsukamoto Y, Ichise H, Kakuda H, et al. Intake of fermented soybean (natto) increases circulating vitamin K2 (menaquinone-7) and gamma-carboxylated osteocalcin concentration in normal individuals. Journal of Bone and Mineral Metabolism 2000;18(4):216-222.
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