Clinical and biological activity of soy protein powder supplementation in healthy male volunteers.
OBJECTIVE
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.


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-beta and ER-alpha 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-beta using a reporter estrogen receptor assay in yeast.


CONCLUSIONS
Soy protein powder decreases serum testosterone levels in healthy men and acts as an ER-beta agonist; the significance of this biological effect with respect to cancer prevention needs further study.
Goodin
Susan
S
Department of Medicine, University of Medicine and Dentistry of New Jersey/Robert Wood Johnson Medical School, New Brunswick, NJ 08903-2681, USA. goodin@umdnj.edu
Shen
Francisco
F
Shih
Weichung J
WJ
Dave
Nisha
N
Kane
Michael P
MP
Medina
Patrick
P
Lambert
George H
GH
Aisner
Joseph
J
Gallo
Michael
M
DiPaola
Robert S
RS
D000328:Adult; D006801:Humans; D007986:Luteinizing Hormone / Q000097:blood*; D008297:Male; D008875:Middle Aged; D030262:Soybean Proteins / Q000494:pharmacology*; D018709:Statistics, Nonparametric; D013739:Testosterone / Q000097:blood*
D030262:Soybean Proteins; D013739:Testosterone; D007986:Luteinizing Hormone