Research: CROUSE and colleagues,

Listed in Issue 28

Abstract

CROUSE and colleagues, Department of Medicine, Wake Forest University School of Medicine, Winston-Salem, NC 27157 USA jrcrouse@wfubmc.edu  write that isolated soy protein reduces plasma concentrations of total and low-density lipoprotein (LDL) cholesterol. The authors set out to identify the agent(s) responsible for the cholesterol-lowering effect of soy in mildly hypercholesterolaemic people, using isoflavones isolated together with soy protein or soy protein itself.

Background

Methodology

The authors conducted a double-blind randomised parallel, single-centre trial. 156 healthy men and women with LDL cholesterol levels between 3.62 mmol/L (140 mg/dl) and 5.17 mmol/L (100 mg/dl) were recruited by advertisement from the community and provided instruction in the National Cholesterol Education Programme Step I diet. The intervention consisted of one of 5 daily diets: 25 g of casein for isoflavone-free comparison, or 25 g of isolated soy protein containing 3, 27, 37, or 62 mg isoflavones. The main outcome measures were change and percent change from baseline in plasma concentrations of triglycerides and total, LDL, and high-density lipoprotein cholesterol following 9 weeks.

Results

Compared with casein, isolated soy protein with 62 mg isoflavones lowered total and LDL cholesterol levels by 4% respectively. Patients with LDL cholesterol levels in the top half of the population experienced comparable reductions of 9% and 10% respectively. In this group, isolated soy protein with 37 mg of isoflavones reduced total and LDL cholesterol levels by 8%; there was a dose-response effect of increasing amounts of isoflavones upon total and LDL cholesterol. Plasma concentrations of triglycerides and high-density lipoprotein cholesterol were unaffected. Ethanol-extracted isolated soy protein with 3 mg isoflavones did not significantly reduce plasma concentrations of total or LDL cholesterol.

Conclusion

Naturally occurring isoflavones isolated with soy protein reduced plasma concentrations of total and LDL cholesterol without affecting triglyceride concentrations or high-density lipoprotein cholesterol in mildly hypercholesterolaemic volunteers following a National Cholesterol Education Programme Step I diet. Isolated, ethanol-extracted soy protein did not significantly reduce plasma concentrations of total or LDL cholesterol.

References

Crouse JR 3rd et al. A randomized trial comparing the effect of casein with that of soy protein containing varying amounts of isoflavones on plasma concentrations of lipids and lipoproteins. Archives of Internal Medicine 159(17): 2070-6. 27 Sep 1999.

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