Altered Time Course of Urinary Daidzein and Genistein Excretion During Chronic Soya Diet in Healthy Male Subjects

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Abstract

Soybean consumption is associated with reduced rates of prostate and other cancers, possibly due in part to the presence of isoflavones. The metabolism and disposition of these soya-derived phytoestrogens after chronic soya exposure were studied on a metabolic unit in six healthy males (21–35 yrs of age) who consumed an unrestricted hospital diet and a 12-oz portion of soymilk with each meal for one month. The daily isoflavone intake was about 100 mg of daidzein (mostly asdaidzin) and about 100 ofmg ofgenistein (mostly as genistin). At two-week intervals, excretion of isoflavones in urine was studied, during which time the subjects consumed a constant basal diet for three to four days, ingested the full daily 36-oz portion of soymilk within 30 minutes each day for one to two days, and collected urine continuously. The urinary recovery of ingested daidzin plus daidzein (46.9 ± 15.2%, mean ± SD) and genistin plus genistein (14.6 ± 9.2%) did not change with prolonged soya ingestion. The absorption half-lives (tV2) far daidzein and genistein and the appearance t1/2for equol (1 subject) were initially 1.5 ± 0.4,1.9 ± 0.6, and2.2 hours, respectively, and2.5 ± 1.1 (p = 0.06 compared with baseline), 1.4 ±0.9 (p -0.03 compared with baseline), and 4.2 hours, respectively, during one month of soymilk ingestion. The excretion tmfar daidzein, genistein, and equal were initially 2.9 ±0.5, 3.8 ± 0.7, and 5.2 hours, respectively, and 3.9 ±1.2 (p = 0.03), 5.5 ± 1.6 (p = 0.02), and 9.7 hours, respectively, during one month of soymilk ingestion. These results indicate that chronic soya exposure did not induce significant changes in the metabolic pathways of isoflavones but altered the time courses of daidzein and genistein excretion. Thus chronic exposure to soya might prolong the tissue exposure to the presumed biologically active free and unconiugated forms of these isoflavones and thereby enhance their oncovrotective effects.

Original languageEnglish (US)
Pages (from-to)311-323
Number of pages13
JournalNutrition and Cancer
Volume24
Issue number3
DOIs
StatePublished - Jan 1 1995

ASJC Scopus subject areas

  • Medicine (miscellaneous)
  • Oncology
  • Nutrition and Dietetics
  • Cancer Research

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