Re: effect of soy protein isolate supplementation on biochemical recurrence of prostate cancer after radical prostatectomy: a randomized trial.

available at http://jurology.com/ Editorial Comment: Soy protein has long been postulated to carry beneficial effects in men with prostate cancer and women with breast cancer, largely due to a high content of isoflavones, a group of naturally occurring estrogens. In particular an isoflavone called genistein is known to bind to estrogen receptor-beta and exert an antiproliferative effect on prostate cancer cells. In this prospective randomized trial men at high risk for recurrence following radical prostatectomy were randomized to receive a soy protein supplement or placebo daily for up to 20 months. No decrease in the rate of biochemical recurrence was observed among men receiving soy protein. Broad interpretation of trials such as this is difficult owing to a lack of dosing studies with dietary supplements and a wide variety of available soy products with differing concentrations. It is difficult to know if soy supplementation is of no benefit or if the study design explains the result.