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Arch Intern Med. 1999 Sep 27;159(17):2070-6.

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.

Author information

  • 1Department of Medicine, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA. jrcrouse@wfubmc.edu

Abstract

CONTEXT:

Isolated soy protein reduces plasma concentrations of total and low-density lipoprotein (LDL) cholesterol.

OBJECTIVE:

To identify the agent(s) responsible for the cholesterol-lowering effect of soy in mildly hypercholesterolemic volunteers: isoflavones isolated together with soy protein or soy protein itself.

DESIGN:

Double-blind randomized parallel trial.

SETTING:

Single-center study.

PARTICIPANTS:

A total of 156 healthy men and women with LDL cholesterol levels between 3.62 mmol/L (140 mg/dL) and 5.17 mmol/L (200 mg/dL) after instruction in a National Cholesterol Education Program Step I diet and recruited by advertisement from the community.

INTERVENTION:

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 of isoflavones).

MAIN OUTCOME MEASURES:

Change and percent change from baseline in plasma concentrations of triglycerides and total, LDL, and high-density lipoprotein cholesterol after 9 weeks.

RESULTS:

Compared with casein, isolated soy protein with 62 mg of isoflavones lowered total and LDL cholesterol levels by 4% (P = .04) and 6% (P = .01), respectively. In patients with LDL cholesterol levels in the top half of the population studied (>4.24 mmol/L [>164 mg/dL]), comparable reductions were 9% (P<.001) and 10% (P = 001), respectively; in this group, isolated soy protein with 37 mg of isoflavones reduced total (P = .007) and LDL (P = .02) cholesterol levels by 8%, and there was a dose-response effect of increasing amounts of isoflavones on total and LDL cholesterol levels. Plasma concentrations of triglycerides and high-density lipoprotein cholesterol were unaffected. Ethanol-extracted isolated soy protein containing 3 mg of isoflavones did not significantly reduce plasma concentrations of total or LDL cholesterol.

CONCLUSIONS:

Naturally occurring isoflavones isolated with soy protein reduce the plasma concentrations of total and LDL cholesterol without affecting concentrations of triglycerides or high-density lipoprotein cholesterol in mildly hypercholesterolemic volunteers consuming a National Cholesterol Education Program Step I diet. Ethanol-extracted isolated soy protein did not significantly reduce plasma concentrations of total or LDL cholesterol.

PMID:
10510993
[PubMed - indexed for MEDLINE]
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