The effect of isolated soy protein on plasma biomarkers in elderly men with elevated serum prostate specific antigen

J Urol. 2001 Jan;165(1):294-300. doi: 10.1097/00005392-200101000-00082.


Purpose: We performed a randomized double-blind crossover pilot study in elderly men with elevated prostate specific antigen (PSA) on the effects of the daily consumption of 2 soy beverages, each containing 20 gm. of isolated soy protein, on the isoflavone concentration in blood and urine, and on the 3 serum biomarkers cholesterol, PSA and the soluble p105 component of the p185erbB-2 proto-oncogene.

Materials and methods: A total of 34 men supplemented their diet by consuming 1 of 2 soy protein beverages assigned randomly twice daily for a 6-week period. In a second 6-week period they consumed the other soy protein beverage. The beverage ISP+ provided 42 mg. of genistein and 27 mg. of daidzein daily, whereas the other beverage, ISP-, provided only 2.1 and 1.3 mg. of these isoflavones daily, respectively. Blood and 24-hour urine samples were obtained before the study, at 2-week intervals during the study and 2 weeks after study completion.

Results: ISP+ and to a lesser extent ISP- substantially increased the serum concentration and urinary output of the isoflavones and their metabolites. Serum cholesterol was significantly decreased by ISP+ irrespective of the order in which the 2 soy beverages were administered and in apparent correlation with the total isoflavone concentration. There was no significant effect of the soy beverages on serum PSA and p105erbB-2 values.

Conclusions: This study reveals that short-term exposure of elderly men with elevated serum PSA values to soy protein containing isoflavones decreases serum cholesterol but not the serum biomarkers PSA and p105erbB-2.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Aged
  • Biomarkers / blood
  • Cholesterol / blood
  • Cross-Over Studies
  • Double-Blind Method
  • Humans
  • Isoflavones / metabolism
  • Isoflavones / pharmacology
  • Male
  • Middle Aged
  • Pilot Projects
  • Prostate-Specific Antigen / blood*
  • Proto-Oncogene Mas
  • Receptor, ErbB-2 / blood
  • Soybean Proteins / pharmacology*
  • Time Factors


  • Biomarkers
  • Isoflavones
  • MAS1 protein, human
  • Proto-Oncogene Mas
  • Soybean Proteins
  • Cholesterol
  • Receptor, ErbB-2
  • Prostate-Specific Antigen