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

Abstract

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 > or =30 mg soy isoflavones/d for at least 2 y had 5.3-times the probability of producing equol than men who had consumed < or =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.

Severe &amp; Moderate BPH Symptoms in Mid-Aged Men Improve with Isoflavonoid-Equol Treatment: Pilot Intervention Study

“…Previous laboratories, including ours, have shown that isoflavones binding to ER-β in the prostate can down regulate the AR and thus decrease negative androgen hormone actions [28]. Moreover, this may explain how isoflavonoid molecules accumulate in prostate tissue and prostatic fluid after oral supplementation [29,30]. Equol's SERMlike binding to ER-β within the prostate has positive implications in decreasing proliferation, inflammation and carcinogenesis [4,25] and down regulating ER-α which has a negative impact on prostate health [4].…”

Isoflavone metabolism in domestic cats (Felis catus): Comparison of plasma metabolites detected after ingestion of two different dietary forms of genistein and daidzein1

“…It has been suggested that chronic exposure to daidzein may increase the equol-producing capacity of the gut microbiota of mammals (Hedlund et al, 2005). Certain gastrointestinal bacteria are known to be stimulated by exposure to isofl avones (De Boever et al, 2000;Clavel et al, 2005), such that prolonged intake has been associated with altered isofl avone metabolism or absorption, or both, compared with single bolus doses (Lu and Anderson, 1998;Hedlund et al, 2005).…”

Serum prostate-specific antigen but not testosterone levels decrease in a randomized soy intervention among men

“…Some studies have suggested that soy may also affect other sex hormones, such as DHT, estrone and estradiol (Habito et al, 2000;Nagata et al, 2000;Dillingham et al, 2005). Moreover, isoflavones may protect against prostate cancer through non-hormonal mechanisms (Wang et al, 2003;Hedlund et al, 2005). For example, in vitro effects against insulin-like growth factor-1 and subsequent prostate cancer cell growth have been observed (Wang et al, 2003).…”

“…For example, in vitro effects against insulin-like growth factor-1 and subsequent prostate cancer cell growth have been observed (Wang et al, 2003). As soy isoflavones have been detected in much higher concentrations in prostatic fluid than in the serum, they may also act locally (Hedlund et al, 2005). The small (14%) decline in mean serum PSA level on the high soy diet is consistent with an intervention using a soy protein supplement among prostate cancer patients that showed nonsignificant declines in serum PSA and free testosterone in the soy isoflavone supplemented group (Kumar et al, 2004).…”