Effects of protein source and amino acid supplementation on plasma cholesterol in guinea pigs

The effects of three dietary protein treatments were compared on cholesterol content of plasma lipoprotein fractions and oxidative status of liver lipids in adult guinea pigs. All diets were adequate in soluble dietary fiber and well-balanced in fatty acids providing 30% of total energy. After seven weeks dietary treatments, casein compared to soy protein increased cholesterol in a sub-fraction of LDL (low density lipoprotein) with larger molecular weight and in a combination of this sub-fraction of LDL plus VLDL (very low density lipoprotein) taken together. Supplementation of casein diet with glycine, alanine, arginine and cystine tended to decrease cholesterol in the sub-fraction of LDL with larger molecular weight. There was no effect of dietary treatments on thiobarbituric acid reactive substances in lipids extracted from guinea pig liver likely due to the very high vitamin E and C content of the diets. In addition to counteracting the serum cholesterol elevating effects of dietary cholesterol soy protein also appears to attenuate the hypercholesterolemic effects of dietary saturated fatty acids.