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Human Nutrition and Metabolism

Long-Term Dietary Habits Affect Soy Isoflavone Metabolism and Accumulation in Prostatic Fluid in Caucasian Men^1,2

Tammy E. Hedlund³, Paul D. Maroni^*, Paul G. Ferucci^*, Robert Dayton, Stephen Barnes, Kenneth Jones, Ray Moore, Lorraine G. Ogden^**, Kristiina Wähälä, Holly M. Sackett^** and Karen J. Gray

School of Medicine, Department of Pathology, ^* Department of Surgery, Division of Urology, ^** Department of Preventive Medicine and Biometrics, and The University of Colorado Cancer Center, The University of Colorado Health Sciences Center, Denver, CO; Department of Pharmacology & Toxicology, The University of Alabama at Birmingham, Birmingham, AL; and Department of Chemistry, The University of Helsinki, Helsinki, Finland

³To whom correspondence should be addressed. E-mail: Tammy.Hedlund{at}UCHSC.edu.

The soy isoflavones daidzein and genistein are believed to reduce prostate cancer risk in soy consumers. However, daidzein can be metabolized by the intestinal flora to form a variety of compounds with different bioactivities. In the current study, we investigated the influence of long-term dietary habits on daidzein metabolism in healthy Caucasian men (19–65 y old). A secondary goal was to compare plasma and prostatic fluid concentrations of 5 isoflavonoids: genistein, daidzein, equol, dihydrodaidzein, and O-desmethylangolensin. Baseline plasma levels of isoflavonoids were quantitated in 45 men by HPLC-electrospray ionization-MS. Participants then consumed a soy beverage daily for 1 wk, and post-soy isoflavonoid levels were quantitated in plasma and prostatic fluid. Equol was the only metabolite that appeared to be influenced by routine dietary habits. Stratified analyses revealed that men who had consumed 30 mg soy isoflavones/d for at least 2 y had 5.3-times the probability of producing equol than men who had consumed 5 mg/d (P = 0.014). Additionally, those men who consumed animal meat regularly had 4.7-times the probability of producing equol than men who did not consume meat (P = 0.023). Equol production was not linked to age, BMI, or the consumption of yogurt, dairy, fruit, or American-style fast food. Daidzein and its metabolites (but not genistein) were typically present at higher levels in prostate fluid than plasma (median = 4–13 times that in plasma). In conclusion, our data suggest that the ability of Caucasian men to produce equol is favorably influenced by the long-term consumption of high amounts of soy and the consumption of meat. Last, the high concentrations of isoflavonoids in prostatic fluid increases the potential for these compounds to have direct effects in the prostate.

KEY WORDS: • soy isoflavones • Seventh Day Adventist • prostate cancer

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