Positive Health Online

Abstract

GARDNER and colleagues, Stanford Center for Research in Disease Prevention and the Department of Medicine, Stanford University Medical School, Stanford, CA, USA, cgardner@stanford.edu investigated the effects of soy protein and isoflavones on plasma lipid concentrations in postmenopausal moderately hypercholesterolaemic women.

Background

Evidence exists that soy protein may have a hypocholesterolaemic effect. Isoflavones in soy may be partly responsible for this effect, but few studies have looked at the separate effects of soy protein and isoflavones.

Methodology

This randomized, double-blind, placebo-controlled clinical trial involved 94 postmenopausal women with moderate hypercholesterolaemia . The women completed a 4-week run-in phase when they consumed a milk protein supplement. Subjects were then randomly assigned to 12 weeks of dietary protein supplementation (42 grams/day) with: 1) a milk protein (Milk group); 2) a soy protei n containing trace amounts of isoflavones (Soy- group); or 3) a soy protein containing 80 mg aglycone isoflavones (Soy+ group).

Results

LDL-cholesterol levels decreased more in the Soy+ than in the Soy- group (0.38 versus 0.09 mmol/l; p=0.005), but neither of these changes was significantly different from the 0.26 mmol/l decrease seen in the Milk group. Similar findings were obtained for total cholesterol levels. There were no significant differences in HDL-cholesterol or triacylglycerol levels between the 3 treatment groups.

Conclusion

The results suggest total and LDL-cholesterol lowering effects attributable to the isoflavone-containing fraction . However, the lowered LDL-cholesterol in the Milk group and the lack of significant difference between either Soy group and the Milk group suggest that the observed changes may have been due to other factors related to participation in the study.

References

Gardner CD et al. The effect of soy protein with or without isoflavones relative to milk protein on plasma lipids in hypercholesterolemic postmenopausal women. The American Journal of Clinical Nutrition 73 (4): 728-35. Apr 2001.

Comment

Readers following the ongoing soy debate will be especially interested in the above results, which appear to raise yet more questions about what are the factor(s) responsible for the total and LDL-cholesterol lowering effects.