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Nutrient - Fermented soy proves more bioavailable

By Holly Taylor BSc (Hons) DipCNM MBANT NTCC

Despite numerous studies reporting the potential health benefits of soy, controversy and contradiction still exists, particularly in terms of how easily soy isoflavones are absorbed and used by the body.

Soy isoflavones are well-known phytoestrogens – active substances derived from plants that have an oestrogen-balancing effect in the body. They have been most extensively studied for their role in cancer prevention and menopause management.

In unfermented soya, 98% of these isoflavones are present in their glycoside form, but in Japan and other Eastern countries, soy is traditionally eaten as fermented whole foods, such as miso, tempeh and natto. This fermentation converts the isoflavones glycosides into their activated aglycone form.

In a new study from Japan, scientists carried out a randomised, double-blind, crossover trial to compare the absorption of fermented and non-fermented soya in a group of postmenopausal women. The women were each given a single dose of fermented or non-fermented soy powder dissolved in hot water. Blood and urine samples were then taken at regular intervals to measure how well the soy isoflavones were absorbed by the women’s bodies.

The results showed that the fermented soy powder was absorbed “faster and in greater amounts”, compared to the non-fermented forms. In fact, 25% more isoflavone was absorbed from the fermented soy powder at a rate five times faster than for the unfermented powder. 

Editor’s note – this new research further supports the findings on fermented soy reported in last month’s Nutrition News.

Article References

Okabe Y. Higher bioavailability of isoflavones after a single ingestion of aglycone-rich fermented soybeans compared with glucoside-rich non-fermented soybeans in Japanese postmenopausal women. J Sci Food Agric 2010 [Epub ahead of print].

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