Bioavailability of soybean isoflavones from aglycone and glucoside forms in American women.
BACKGROUND
Test results on the bioavailability of isoflavones in the aglycone or glucoside form in Eastern and Western human subjects are contradictory.


OBJECTIVE
The objective was to investigate the bioavailability of the soy isoflavones daidzein and genistein in American women with typical American dietary habits after ingestion of the aglycone or glucoside form of isoflavones.


METHODS
Fifteen American women aged 46 +/- 6 y participated in a randomized, double-blind study. Blood samples were collected 0, 1, 2, 4, 8, 12, 24, and 48 h after consumption of aglycone or glucoside tablets with breakfast. The plasma curves for daidzein, genistein, and equol were constructed and the postprandial maximum concentration (C(max)), time to the maximum concentration (t(max)), and area under the curve (AUC) were determined.


RESULTS
Isoflavone concentrations peaked early (1-2 h) in plasma and peaked again at 4-8 h. Mean C(max), t(max), and AUC values for genistein were not significantly different after ingestion of aglycone or glucoside. However, C(max) and AUC values, but not t(max), were significantly higher for daidzein after aglycone ingestion, which was partly due to its higher content in the aglycone tablets. Equol appeared after 4 h and remained elevated after 48 h. Despite a higher content of daidzein in the aglycone tablets, the AUC for equol was significantly higher after ingestion of the glucoside tablets, probably because of the metabolic action of intestinal bacteria during the long intestinal transit time of glucoside.


CONCLUSIONS
The apparent bioavailability of genistein and daidzein is not different when consumed as either aglycone or glucoside by American women.
Zubik
Ligia
L
Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111, USA.
Meydani
Mohsen
M
D000328:Adult; D019540:Area Under Curve; D001682:Biological Availability; D002839:Chromans / Q000493:pharmacokinetics; D004311:Double-Blind Method; D060754:Equol; D005260:Female; D019833:Genistein / Q000493:pharmacokinetics*; D006801:Humans; D007529:Isoflavones / Q000493:pharmacokinetics*; D008875:Middle Aged; D013025:Glycine max / Q000737:chemistry; D013997:Time Factors; D014481:United States
C007610:4',7-dihydroxy-3,4-dihydroisoflavone; D002839:Chromans; D007529:Isoflavones; D060754:Equol; C004742:daidzein; D019833:Genistein