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SECOND INTERNATIONAL SYMPOSIUM
ON THE ROLE OF SOY
IN PREVENTING AND TREATING CHRONIC DISEASESeptember 15-18, 1996
Brussells, Belgium
POSTER ABSTRACTSInteractions between soy protein and soy fiber on lipid metabolism in the rat.
Moundras, C. Rémésy, M-A. Levrat, S.R. Behr & C. Demigné.
Laboratoire des Maladies Métaboliques et Micronutri-ments, I.N.R.A. de Clermont Ferrand/Theix, 63122 St-Genès-Champanelle, France and Ross Products Division, Abbott Laboratories, Columbus, OH 43216, USA.
To investigate the mechanisms by which soy products exert their cholesterol-lowering effects, rats were adapted to semi-purified diets which differed with respect to dietary protein (casein or soy protein, 16% in the diet) and polysaccharides (digestible starch alone or digestible starch/soy fiber). Although a similar stimulation of the fecal excretion of bile acids was obtained in rats fed soy protein of soy fiber diets, cholesterolemia or liver HMG CoA reductase; with soy fiber, HMG CoA reductase induction was marginal and there was the cholesterol-effect classicaly observed with this type of fiber. In the present model, soy protein tended to enhance LDL and HDL1 cholesterol, whilst soy fiber appeared effective to lower cholesterol in LDL and HDL fractions. When both soy products were present in the diet, there was a maximal excretion of bile acids in feces and cholesterolemia was depressed compared to fiber-free conditions, but a high degree of HMG CoA reductase induction was still present. A potent triglyceride-lowering effect was observed with soy protein or soy fiber, in parallel to a reduced activity of liver FAS as well as to a lowerd insulin/glucagon ratio. In rats fed soy protein at marginally deficient level, imbalanced amino acid supply may significantly alter lipid metabolism. Soy fiber interferes with these effects of soy protein: by counteracting its effects on cholesterolemia (although HMG CoA reductase induction was not affected), or by reinforcing its triglyceride-lowering effect. In fact, in well-balanced diets where the methionine deficiency of soy protein is compensated for by other types of proteins, complex soy products are certainly effective as lipid lowering compounds but other parameters (e.g. lipoprotein susceptibility to peroxidation) have also to be considered.
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