Abstract
Purpose: To determine if a commonly used soy protein supplement exhibits biological activity in vivo and in vitro, we evaluated an over-the-counter soy protein powder supplement using blood from healthy male volunteers and in an estrogen receptor in vitro assay.
Subjects and Methods: We recruited healthy male volunteers 18 years of age or older that were in good health. Treatment consisted of consuming two scoops (56 g) of pure soy protein powder (Puritan's Pride, Oakdale, NY) daily for 28 days. Serum testosterone and luteinizing hormone (LH) levels were collected on days −7, 0, 14, and 28 of therapy, and day 42. A reporter estrogen receptor (ER) assay was used to determine the effect on ER-β and ER-α in vitro.
Results: Twelve subjects were enrolled with a mean age of 32.25 years (range 25 to 47). Serum testosterone decreased 19%(±22%) during the 4-week use of soy protein powder (P = 0.021) and increased within 2 weeks after we discontinued soy protein powder. Serum LH concentrations decreased during the 4-week use of soy protein powder then increased within 2 weeks after we stopped the soy protein powder, but the changes did not reach statistical significance (P = 0.20). Soy protein powder was found to induce agonist activity to ER-β using a reporter estrogen receptor assay in yeast.
Conclusion: Soy protein powder decreases serum testosterone levels in healthy men and acts as an ER-β agonist; the significance of this biological effect with respect to cancer prevention needs further study. (Cancer Epidemiol Biomarkers Prev 2007;16(4):829–33)
- soy protein powder
- Genitourinary cancers: prostate
- Natural products
- Steroid hormones and receptors
Footnotes
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Grant support: P30 CA72720-01-03 and National Cancer Institute–Complementary and Alternative Medicine 562068.
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
- Accepted January 23, 2007.
- Received October 20, 2006.
- Revision received January 2, 2007.
Volume 16, Issue 4
