Elsevier

The Journal of Nutrition

Volume 133, Issue 10, October 2003, Pages 3110-3116
The Journal of Nutrition

Rapid Gut Transit Time and Slow Fecal Isoflavone Disappearance Phenotype Are Associated with Greater Genistein Bioavailability in Women1,2

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The bioavailability of soybean isoflavones varies widely among individuals due to many factors, including activities of gut microflora. To characterize factors that affect fecal isoflavone disappearance phenotype and isoflavone bioavailability in women, 35 Asian and 33 Caucasian women, 18–43 y of age, provided fecal samples for anaerobic incubation with isoflavones in vitro at two times 5 mo apart (Phases I and II). Diet, physical activity and health history were investigated at these times. A single dose of soymilk powder [1.2 mg (4.57 μmol) total isoflavone/kg body] was given to all subjects with breakfast in phase II. Daidzein and genistein from fecal incubations, urine and fecal samples were measured by reverse-phase HPLC. Three significantly different daidzein and two genistein disappearance phenotypes were identified from fecal isoflavone incubations. More Asians than Caucasians were identified within the high daidzein disappearance phenotype. Caucasians and Asians differed significantly in daily intake of red meat (0.3 ± 0.1 vs. 1.0 ± 0.1 servings/d), dairy foods (2.9 ± 0.2 vs. 1.2 ± 0.2 servings/d) and insoluble dietary fiber (3.6 ± 0.3 vs. 1.4 ± 0.3 g). BMI, maximal oxygen uptake (VO2 max) and physical activity level were significantly greater in Caucasians than in Asians. Asian subjects of the low genistein disappearance phenotype had more rapid gut transit time (GTT) and greater isoflavone bioavailability as reflected in urinary genistein excretion than did Asians of the high genistein disappearance phenotype (GTT, 40 ± 8 vs. 63 ± 5 h; 11.0 ± 2.7 vs. 4.0 ± 1.7% of ingested genistein excreted in urine). Caucasians of both genistein disappearance phenotypes had longer GTT than did Asian subjects (84 ± 5 vs. 56 ± 6 h) and resembled Asians of the high genistein disappearance phenotype in genistein bioavailability. Relatively rapid GTT coupled with a low fecal isoflavone disappearance phenotype as occurred in Asian but not Caucasian subjects produced greater genistein bioavailability, as reflected in urinary genistein excretion.

Key words:

isoflavone
genistein
degradation
gut transit time
ethnicity

Abbreviations:

BHI
brain heart infusion
DD H2O
distilled deionized water
Dk
daidzein disappearance rate constant
Gk
genistein disappearance rate constant
GTT
gut transit time
THB
2,4,4′-trihydroxybenzoin
VO2 max
maximal oxygen uptake

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1

Presented in part at Experimental Biology, April 2000, San Diego, CA [Zheng, Y., Lebepe, S., Hu, J., Zhang, Y., Murphy, P. A., Alekel, L., Franke, W. & Hendrich, S. (2000) Ethnicity and gut transit time influence bioavailability of soybean isoflavone in women. FASEB J. 14: LB183].

2

Journal paper No. J-17673 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA. This work was supported in part by USDA Fund for Rural America, grant No. 97–362155190 and by the Iowa Agriculture & Home Economics Experiment Station, Project No.3302.