Sharma, P., Wisniewski, A., Braga-Basaria, M., Xu, X., Yep, M., Denmeade, S., … Basaria, S. (2009). Lack of an effect of high dose isoflavones in men with prostate cancer undergoing androgen deprivation therapy. Journal of Urology, 182, 2265–2272.

The study evaluated the effects of high dose isoflavones, equivalent to that consumed by Asian populations, on the consequences of androgen deprivation therapy (ADT) for prostate cancer, such as sexual dysfunction, poor QOL, vasomotor symptoms, and altered cognition.

The intervention contained 20 gm Revival® (Physicians Laboratories) soy protein consisting of 160 mg total isoflavones as powder to be mixed with beverages. Placebo contained 20 gm whole milk protein and similar nutrients as the intervention except for isoflavones. Active and placebo powders appeared and tasted similar. Supplements were ingested once daily for 12 weeks, and dispensed at the baseline and 6-week visits. Data were gathered at study baseline, and weeks 6 and 12. Men tolerated the compound well with only one withdrawing from study because he disliked its taste. Overall compliance was high at approximately 80%. Compliance was based on the number of sachets returned by each patient at treatment weeks 6 and 12. 

This was a 12-week pilot trial of high-dose isoflavones ingested by 39 men with prostate cancer undergoing ADT. Participants were randomly assigned to receive 20 gm soy protein containing 160 mg total isoflavones (17) versus taste-matched placebo (20 gm whole milk protein).  After enrollment, men were instructed to refrain from ingesting any kind of soy product during the 12-week study period. Thirty-three (33) completed the study.

• Inclusion criteria: Men 21 years old or older undergoing medical or surgical ADT for at least three months.
• Exclusion criteria: Hepatic, renal, thyroid or neurologic disease, active psychiatric disorder, current chemotherapy or glucocorticoids, appetite or weight promoting agents, substance abuse, triglycerides greater than 500 mg/dl, or allergy to soy protein or cow milk.

Men already on soy supplements were washed out for at least three months before entry.

Study was a randomized, double-blind, placebo-controlled trial.

Men were not well matched for hot flashes, with the isoflavones group reporting higher scores (increased distress) than men on placebo at baseline and at study end. However, within-group analysis showed no significant changes in the vasomotor distress score in either group. Using the Kupperman scale, men on isoflavones did not show any significant improvement in hot flashes compared to those on placebo. At 12 weeks, there were no significant differences between the two groups in any outcome measure. No safety issues were found during the study.

This pilot study of high-dose isoflavones in androgen deprived men showed no significant improvement in cognition, vasomotor symptoms, or any other aspect of QOL measures compared to placebo.

This pilot study had a small sample size and short treatment duration. Future studies should use variable doses of isoflavones for a longer period before ruling out beneficial isoflavone effects in this population.