COMPARATIVE EFFECTS OF PURIFIED AND HUMAN-TYPE DIETS ON CHOLESTEROL-METABOLISM IN THE RAT

Purified diets and others composed of foods commonly eaten by humans either low or 0.5% in cholesterol and low in fiber or containing plant or animal acid polysaccharides and 0.5% cholesterol were fed to adult female Sprague-Dawley rats for 10 weeks. All eight diets contained 28% beef fat and were comparable with respect to total calories as well as the relative amounts of fat, carbohydrate, and protein. The average serum cholesterol level of the rats which consumed the high cholesterol diet without added acid polysaccharides was 187 mg/dl. Without added cholesterol it was significantly lower (95 mg/dl). Average serum cholesterol level of rats fed high cholesterol purified diets with pectin (a plant acid polysaccharide) or with chondroitin sulfate isomers (an animal acid polysaccharide) were similar and intermediate (118 mg/dl and 126 mg/dl, respectively), but were not significantly different (P > 0.05) from serum cholesterol levels of rats fed the low cholesterol purified diet or the human-type diets. There was no difference in average serum cholesterol levels among the four groups of rats ingesting the human-type diets, they being equal to that of rats fed the low cholesterol, low fiber purified diet. The homeostatic effect of the human-type diets could not be explained on the basis of enhanced fecal excretion of neutral sterols or bile acids nor increased activity of cholesterol 7α-hydroxylase. The specific activity of hepatic 3-hydroxy-3-methylglutaryl coenzyme-A reductase tended to be lower in rats fed the human-type diets.