Soy isoflavone bioavailability test shows which forms are best: Study

By Stephen Daniells

- Last updated on GMT

Related tags: Soybean

Isoflavones in the aglycone form – as found naturally in fermented soy foods – are more bioavailable than the glucoside-form from non-fermented soy, says a new study from Japan.

Consumption of both types of isoflavone forms by healthy postmenopausal Japanese women showed that the aglycone-form was absorbed “faster and in greater amounts”, ​compared to the glucoside forms, according to findings published in the Journal of the Science of Food and Agriculture​.

Twenty-five percent more isoflavone was absorbed in the aglycone-form and this was absorbed five times faster than the glucoside forms, reported researchers from Ajinomoto Co., Ltd.

The issue

Soy isoflavones are well known phytoestrogens - active substances derived from plants that have a weak estrogen-like action. They have been studied for their role in cancer prevention and slowing down the ageing process in peri-menopausal women, and have proved to be a popular alternative to hormone replacement therapy for those wishing to control menopause symptoms without resorting to drugs.

Despite numerous studies reporting the potential health benefits of soy, controversy and contradiction still exists, particularly in terms of how bioavailable the isoflavone forms (glycoside versus aglycone) are.

Some studies have reported no difference between bioavailability of the isoflavone type, whereas others have reported higher bioavailability for aglycones (for example, Journal of Nutritional Biochemistry​, Volume 20, Pages 227-234).

The new study adds to this body of science, and involved 11 healthy postmenopausal Japanese women aged between 49 and 65. The randomised, double-blind, crossover trial involved giving the women a single dose of fermented or non-fermented soy powder dissolved in hot water. Both interventions provided 95 micromoles of isoflavones per 23 gram serving.

The fermented version contained 90.6 micromoles of aglycones while the nonfermented powder contained 81.9 micromoles of isoflavones were in the glucoside form.

Findings

Results showed that the aglycone form reached a maximum blood value much quicker than the glucoside form: one versus five hours, and that the levels were approximately 25 percent greater following consumption of the aglycone form.

“The food matrix affects the time and way of food passage through the intestine,”​ explained the researchers, led by Ajinomoto’s Yuki Okabe. “Further studies are examining the difference between supplements and foods containing isoflavones. No consensus has been established yet, and studies with appropriate design and precise consideration of various factors are needed.”

Source: Journal of the Science of Food and Agriculture
Published online ahead of print, doi: 10.1002/jsfa.4228
“Higher bioavailability of isoflavones after a single ingestion of aglycone-rich fermented soybeans compared with glucoside-rich non-fermented soybeans in Japanese postmenopausal women”
Authors: Y. Okabe, T. Shimazu, H. Tanimoto

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