EFFECTS OF DIETS RICH IN FERMENTABLE CARBOHYDRATES ON PLASMA-LIPOPROTEIN LEVELS AND ON LIPOPROTEIN CATABOLISM IN RATS

This study was conducted to examine the effects of a combination of several dietary fibers (5% guar gum, 5% apple pectin, 15% wheat bran, 22% soybean fiber) and crude potato starch (23%) on plasma lipids and lipoproteins and on liver lipid concentration in rats fed a diet containing either 15% lard or 5% oil with or without dietary cholesterol/cholic acid. Male Wistar rats ate the test diets for 3 wk. The incorporation of fiber and crude potato starch into the diet resulted in a significant enlargement of the cecum; it also increased the concentration of volatile fatty acids and the pool of acetate, propionate and butyrate. Feeding this fermentable carbohydrate decreased plasma cholesterol and triglyceride levels in rats given a low fat diet and prevented the expected rise in plasma cholesterol and triglycerides in rats fed cholesterol/cholic acid or lard. Further studies of high density lipoprotein (HDL) composition, 3-hydroxy-3-methyl-glutaryl coenzyme A reductase (HMG-CoA reductase) activity and 125I-labeled human low density lipoprotein (LDL) turnover were done in the group fed the low fat diet without added cholesterol/cholic acid. The study of the HDL fraction in rats fed a diet rich in fermentable carbohydrates demonstrated a decrease in the HDL1 subpopulation and in the proportion of apolipoprotein E. Plasma clearance of intravenously injected 125I-labeled LDL was faster in rats fed this diet than in rats fed the fiber-free diet. In the liver, cholesterol and triglyceride levels were depressed whereas the activity of HMG-CoA reductase was increased. In short, this study suggests that a complex fermentable carbohydrate formulation has a very efficient cholesterol-lowering action and affects various mechanisms of cholesterol homeostasis.