Randomized, Placebo-Controlled Six-Month Intervention Study of Soy Protein Isolate in Men with Biochemical Recurrence after Radical Prostatectomy: A Pilot Study

Abstract

There is evidence to suggest that soy may be beneficial for prostate cancer patients, but few randomized trials have addressed this. We examined the effect of 6–8 mo soy protein supplementation on prostate specific antigen (PSA) serum levels in men who recurred (PSA > 0.1 ng/ml) within three years of prostatectomy. Sixteen men were randomized to 20 g soy protein (∼24–26/day genistein; ∼40–43/day total isoflavones) or casein placebo. PSA was measured at base line and at 1, 2, 4, and 6–8 mo. Serum genistein levels greatly increased from baseline and cholesterol decreased in the soy group. In both treatment arms PSA increased similarly and PSA doubling times were not different over the 6–8 mo study duration. Two subjects in each group had stable PSA. A literature search for clinical studies of soy, isoflavones, and PSA revealed that supplementation with soy or isoflavones did not affect PSA in virtually all clinical studies identified. Although this study is too small to draw a definitive conclusion on the effect of soy protein on PSA in men with biochemical failure, the null finding in this study is consistent with the results of virtually all reports of soy and soy isoflavones in the literature.

Acknowledgments

Solae LLC generously donated the intervention materials. The authors are grateful to Drs. Herbert Lepor and Samir Taneja (NYU), and Pablo Torre (VA) for their help in recruiting subjects to this study. We also acknowledge Dr. Anne Zeleniuch-Jacquotte for help with study design. And we would not have been able to conduct this study without the generous participation of the men who were willing to be study subjects.

Disclosure Statement

No potential conflict of interest was reported by the authors. Neither the funding agency nor Solae had any influence on the design of the study nor on the analyses, interpretation, or implementation of the data.

Additional information

Funding

This work was supported in part by the National Institutes of Health under grants U01 CA072290 and P50 CA16087.