Bioavailability of soybean isoflavones from aglycone and glucoside forms in American women1234

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ABSTRACT

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.

Design:

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 (Cmax), time to the maximum concentration (tmax), 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 Cmax, tmax, and AUC values for genistein were not significantly different after ingestion of aglycone or glucoside. However, Cmax and AUC values, but not tmax, 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.

Conclusion:

The apparent bioavailability of genistein and daidzein is not different when consumed as either aglycone or glucoside by American women.

KEY WORDS

Isoflavones
daidzein
genistein
equol
glucoside
aglycone

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1

From the Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston.

2

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not reflect the views or policies of the US Department of Agriculture. Mention of trade names, commercial products, or organizations does not imply endorsement by the US government.

3

Supported by the US Department of Agriculture agreement no. 58-1950-9-001. The soy isoflavone tablets used were a gift from Kikkoman Corp, Noda, Japan.

4

Reprints not available. Address correspondence to M Meydani, Vascular Biology Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, 711 Washington Street, Boston, MA 02111. E-mail: [email protected].