Bioavailabilty of isoflavones tested with Thai women.

Isoflavones research

Pharmacokinetics of isoflavones, daidzein and genistein, after ingestion of soy beverage compared with soy extract capsules in postmenopausal Thai women.

Author: E. Anupongsanugool, S. Teekachunhatean, N. Rojanasthien, S. Pongsatha, and C. Sangdee.
Publication: BMC Clin Pharmacol. 2005 Mar 3;5(1):2.

Estrogen deficiency during menopause causes symptoms such as accelerated bone loss and hearth diseases. Hormone replacement therapy is often used to ease menopausal symptoms. However, the Women's Health Initiative found that estrogen significantly increases the risk of stroke and could increase the incidence of endometrial cancer. Natural therapies, which do not have these side effects, would offer an attractive alternative. Isoflavones offer an attractive alternative because they seem to protect against breast and endometrial cancer. Isoflavones have fewer side effects and offer additional health benefits. Many commercial isoflavones rich soy capsules extract are now available and offer an alternative to soy foods.
There has been no study that compares bioavailability of isoflavones from soy extract and natural soy foods. The purpose of this study was to compare the bioavailability of isoflavones from soy beverage and from a commercial isoflavones rich soy extract. The study was conducted on postmenopausal Thai women.

A total of 12 postmenopausal Thai women, aged between 46 and 61 years participated in this study. The same women received two different isoflavones sources:

Group 1: received soy extract capsules containg 7.79 mg daidzin and 22.57 mg genistin.
Group 2 received a soy beverage made from 15 g of soy flour, containing 9.27 mg daidzin and 10.5 mg genistin.

Blood samples of the women were taken during a period of 32 hours and analyzed for plasma daidzein and genistein concentrations.

The study found that the bioavailability of daidzein, following an oral administration of soy beverage was slightly (but significantly) less than that of soy extract capsules. The bioavailability of genistein was comparable for both groups.