Soy consumption and phytoestrogens: effect on serum prostate specific antigen when blood lipids and oxidized low-density lipoprotein are reduced in hyperlipidemic men.
OBJECTIVE
Herbal remedies high in phytoestrogens have been shown to reduce serum prostate specific antigen (PSA) and have been proposed as a treatment for prostate cancer. Soy proteins used to lower serum cholesterol are rich sources of phytoestrogens. Therefore, we assessed the effect of soy consumption on serum PSA in men who had participated in cholesterol lowering studies.


METHODS
For 3 to 4 weeks 46 healthy middle-aged men with a range of starting PSA values took soy (mean 44 gm. soy protein daily, 116 mg. isoflavones daily) or control foods, and a subgroup of men took a lower level of soy supplements for 3 months. PSA was measured at the start and end of each treatment.


RESULTS
Soy had no significant effect on serum total or free PSA, independent of PSA starting value or isoflavone intake. The lack of effect on PSA was seen, although soy intake was sufficient to reduce low-density lipoprotein cholesterol (5.8 +/- 2.2%, p = 0.012), the estimated coronary heart disease risk (6.1 +/- 2.8% for 10 years, p = 0.032) and the serum concentration of oxidized low-density lipoprotein measured as conjugated dienes (9.5 +/- 3.4%, p = 0.008) in the 3 to 4-week study. In addition, the lack of effect of soy on PSA persisted for the 3 months of the extended study.


CONCLUSIONS
At levels of soy intake which reduce low-density lipoprotein cholesterol any potential benefits of soy consumption on prostate cancer are likely to occur for reasons other than alterations in hormone activity.
Jenkins
David J A
DJ
Clinical Nutrition and Risk Factor Modification Center, St. Michael's Hospital, 61 Queen St. East, Toronto, Ontario, Canada M5C 2T2.
Kendall
Cyril W C
CW
D'Costa
Mario A
MA
Jackson
Chung-Ja
CJ
Vidgen
Edward
E
Singer
William
W
Silverman
Jason A
JA
Koumbridis
George
G
Honey
John
J
Rao
A Venket
AV
Fleshner
Neil
N
Klotz
Laurence
L
D000328:Adult; D000368:Aged; D002784:Cholesterol / Q000097:blood*; D004968:Estrogens, Non-Steroidal / Q000494:pharmacology*; D006801:Humans; D006949:Hyperlipidemias / Q000097:blood*; D007529:Isoflavones / Q000494:pharmacology*; D008077:Lipoproteins, LDL / Q000097:blood* / Q000187:drug effects; D008297:Male; D008875:Middle Aged; D010084:Oxidation-Reduction; D048789:Phytoestrogens; D028321:Plant Preparations; D017430:Prostate-Specific Antigen / Q000097:blood* / Q000187:drug effects; D030262:Soybean Proteins / Q000494:pharmacology*
D004968:Estrogens, Non-Steroidal; D007529:Isoflavones; D008077:Lipoproteins, LDL; D048789:Phytoestrogens; D028321:Plant Preparations; D030262:Soybean Proteins; D002784:Cholesterol; D017430:Prostate-Specific Antigen