Impact of 18-Month Soy Protein Supplementation on Steroid Hormones and Serum Biomarkers of Angiogenesis, Apoptosis, and the Growth Hormone/IGF-1 Axis: Results of a Randomized, Placebo-Controlled Trial in Males Following Prostatectomy

Abstract

Many studies have addressed the effects of dietary supplementation with soy protein on cancer risk and mortality, but there are only few randomized studies with soy in males. We used serum samples from a two-year trial of soy protein isolate supplementation in middle-aged to older males at risk of recurrence of prostate cancer after radical prostatectomy to determine soy effects on steroid hormones involved in prostate cancer (testosterone, SHBG, and estradiol) and explore the effects on biomarkers of the growth hormone/IGF-1 axis, apoptosis, and angiogenesis. Compared with a casein-based placebo, 18 mo, of consumption of 19.2 g/day of whole soy protein isolate containing 24 mg genistein-reduced circulating testosterone and SHBG, but not free testosterone, and did not affect serum concentrations of estradiol, VEGF, IGF-1, IGFBP-3, IGF-1/IGFBP-3 ratio, soluble Fas, Fas-ligand, and sFas/Fas-ligand ratio. Thus, soy protein supplementation for 18 mo, affected the androgen axis, but the effects on other cancer biomarkers remain to be more definitively determined. The study was registered at clinicaltrials.gov (NCT00765479).

Acknowledgments

The authors acknowledge the contributions of Dr. Anne Zeleniuch-Jacquotte, a senior investigator of the parent clinical trial. The authors are grateful to Drs. Herbert Lepor and Samir Taneja (NYU) for their help in recruiting subjects to this study. We also acknowledge Dr. Nikola Baumann for help with assay validation. And we would not have been able to conduct this study without the generous participation of all men who were willing to be study subjects.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported in part by the National Institutes of Health under grants U01 CA072290 and R01 CA166195 to MCB, as well as under grants P50 CA16087 and UL1 TR000050, with minor support from the Prevent Cancer Foundation and the United Soybean Board. JHH was supported by a Craig Medical Student Summer Research Fellowship from the UIC College of Medicine. Solae LLC provided the intervention materials. None of the funding agencies or Solae had any influence on the design of the study nor on the analyses, interpretation, or implementation of the data.