The effect of soy protein with or without isoflavones relative to milk protein on plasma lipids in hypercholesterolemic postmenopausal women.
BACKGROUND
Clinical trial data and the results of a meta-analysis suggest a hypocholesterolemic effect of soy protein. The effect may be partially attributable to the isoflavones in soy. Few studies have examined the separate effects of soy protein and isoflavones.


OBJECTIVE
The objective of this study was to determine the effect of soy protein and isoflavones on plasma lipid concentrations in postmenopausal, moderately hypercholesterolemic women.


METHODS
This was a randomized, double-blind, placebo-controlled clinical trial with 3 treatment groups. After a 4-wk run-in phase during which the women consumed a milk protein supplement, the subjects were randomly assigned to 12 wk of dietary protein supplementation (42 g/d) with either a milk protein (Milk group) or 1 of 2 soy proteins containing either trace amounts of isoflavones (Soy- group) or 80 mg aglycone isoflavones (Soy+ group).


RESULTS
LDL-cholesterol concentrations decreased more in the Soy+ group (n = 31) than in the Soy- group (n = 33) (0.38 compared with 0.09 mmol/L; P = 0.005), but neither of these changes was significantly different from the 0.26-mmol/L decrease observed in the Milk group (n = 30). The results for total cholesterol were similar to those for LDL cholesterol. There were no significant differences in HDL-cholesterol or triacylglycerol concentrations between the 3 groups.


CONCLUSIONS
The difference in total- and LDL-cholesterol lowering between the 2 soy-protein supplements suggests an effect attributable to the isoflavone-containing fraction. However, the unexpected LDL-cholesterol lowering observed in the Milk group, and the fact that there was no significant difference between either soy group and the Milk group, suggests that changes may have been due to other factors related to participation in the study.
Stanford Center for Research in Disease Prevention and the Department of Medicine, Stanford University Medical School, Stanford, CA, USA. cgardner@stanford.edu
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Gardner
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Newell
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Cherin
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Haskell
D000368:Aged; D000818:Animals; D001835:Body Weight; D008076:Cholesterol, HDL / Q000097:blood / Q000187:drug effects; D008078:Cholesterol, LDL / Q000097:blood / Q000187:drug effects; D019587:Dietary Supplements; D004311:Double-Blind Method; D015444:Exercise; D005260:Female; D006728:Hormones / Q000097:blood; D006801:Humans; D006937:Hypercholesterolemia / Q000178:diet therapy*; D007529:Isoflavones / Q000494:pharmacology* / Q000627:therapeutic use; D008055:Lipids / Q000097:blood*; D008875:Middle Aged; D008894:Milk Proteins / Q000494:pharmacology* / Q000627:therapeutic use; D017698:Postmenopause; D030262:Soybean Proteins / Q000494:pharmacology* / Q000627:therapeutic use; D014280:Triglycerides / Q000097:blood
D008076:Cholesterol, HDL; D008078:Cholesterol, LDL; D006728:Hormones; D007529:Isoflavones; D008055:Lipids; D008894:Milk Proteins; D030262:Soybean Proteins; D014280:Triglycerides