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Soy protein enhances cholesterol-lowering effect of plant sterol esters

High plasma cholesterol has been linked to increased risk of coronary heart diseases. This cholesterol can be reduced through dietary components, such as plant sterols (which have a structure similar to that of cholesterol) and soy protein. Plant sterols lower serum cholesterol by competing with cholesterol for incorporation in micelles. The exact mechanism by which soy protein lowers cholesterol is still unknown, but it could reduce the intestinal absorption of cholesterol, stimulate removal of cholesterol from the plasma or change the cholesterol metabolism in the liver. This study aimed to investigate whether the combined effect of plant sterol esters and soy protein or soy isoflavones may have extra cholesterol lowering effects.
Male hamsters were divided in 6 groups, receiving different diets containing either casein (control), plant sterol esters, intact soy protein, soy isoflavones, plant sterol esters and soy protein or plant sterol esters and soy isoflavones. All diets contained same amount of cholesterol (0.08 g cholesterol/100 g food). Compared with the control diet, the plant sterol ester diet and soy protein diet significantly lowered the plasma total cholesterol concentration by 13% and 9%, respectively, whereas the isoflavone diet had no effect. These results indicate that soy protein itself and not isoflavones are responsible for cholesterol lowering action of soy protein. The combination of plant sterol esters and soy protein decreased plasma total cholesterol by as much as 26%. The decrease in plasma cholesterol concentration was mainly in the non-HDL fraction. In addition, plant sterol esters and soy protein significantly decreased plasma triacylglycerol concentration by 37% and reduced cholesterol accumulation in the liver. Plant sterol esters selectively increased faecal excretion of neutral sterols by 190%, whereas soy protein increased faecal excretion of neutral sterols and bile acids by 66% and 130%, respectively. The combination of plant sterol esters and soy protein increased the faecal excretion of neutral sterols and bile acids compared with plant sterol esters and soy protein alone.

The study concluded that a combined treatment with plant sterol esters and soy protein lowers plasma lipids and non-HDL cholesterol more than the individual ingredients.

Source: Soy protein enhances the cholesterol-lowering effect of plant sterol esters in cholesterol-fed hamsters. J Nutr. 2004 Jan;134(1):143-8.

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