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SECOND INTERNATIONAL SYMPOSIUM
ON THE ROLE OF SOY
IN PREVENTING AND TREATING CHRONIC DISEASESeptember 15-18, 1996
Brussells, Belgium
SCIENTIFIC PROGRAM
(Oral Abstracts)Soy and Heart Disease : Hypercholesterolemic Effects of Soy :
Potential MechanismsEffects of Soy Isoflavones on Atherosclerosis: Potential Mechanisms
Mary S. Anthony, Thomas B. Clarkson, J. Koudy Williams
Bowman Gray School of Medicine of Wake Forest University, Winston-Salem, NC.It has long been recognized that diets rich in soy protein reduce atherosclerosis. This effect seems largely explained by soy protein's favorable effects on plasma lipoprotein concentrations; however, the mechanisms responsible are unclear. Several lines of evidence have suggested that the components of soy protein that result in lipid lowering are alcohol extractable. Potter's group found that addition of an alcohol extract of soy protein to a casein-based diet lowered low density lipoprotein (LDL) cholesterol in rats. Lovati and colleagues found that alcohol extract of texturized soy protein increased LDL receptor activity in vitro.
To evaluate the relative contribution of the protein versus the alcohol-extractable components of soy on cardiovascular disease and its risk factors, we fed young cynomolgus males and females diets that differed only with respect to the protein. The diets contained casein/lactalbumin as the source of protein [Casein], alcohol-extracted soy protein isolate [Soy(-)], or unextracted soy protein [Soy(+)]. Plasma lipoproteins were evaluated over 14 months; at the end, eleven males from each group were terminated and atherosclerosis evaluated. Males and females did not differ in their response to the diets.
The Soy(+) group had significantly improved cardiovascular risk factors (i.e. lowered total plasma cholesterol and LDL cholesterol and increased high density lipoprotein [HDL] cholesterol) compared to the other groups. The Soy(-) group had significantly higher HDL cholesterol compared to the Casein group, but other lipoprotein concentrations did not differ. The Casein group had the most atherosclerosis, the Soy(+) group had the least, and the Soy(-) group was intermediate but did not differ significantly from the Casein group. In another study, we found that Soy(+) fed chronically and genistein administered acutely improved coronary artery reactivity compared to Soy (-), having additional implications for coronary heart disease prevention. In summary, alcohol-extractable components of soy protein, likely genistein, appear to be responsible for much of soy's cardiovascular benefits.
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