Title

Mechanisms by which pectin and psyllium reverse the hyperlipidemia induced by high fat/sucrose diets in guinea pigs

Date of Completion

January 1998

Keywords

Agriculture, Food Science and Technology|Biology, Animal Physiology|Health Sciences, Nutrition

Degree

Ph.D.

Abstract

Dietary components such as high fat, simple carbohydrates and cholesterol have been linked to hyperlipidemia. In contrast, pectin (PE) and psyllium (PSY), two sources of soluble fiber have been shown to reduce plasma LDL cholesterol concentrations.^ These studies were undertaken to determine whether PE or PSY would reverse the hyperlipidemia induced by high fat and simple carbohydrate intake, and to assess some of the primary and secondary mechanisms involved. Due to similarities to humans in lipoprotein profile and responses to dietary factors, guinea pigs were chosen as the animal model.^ When given with low or high fat diets, PE and PSY intake resulted in lower plasma and hepatic cholesterol concentrations compared to guinea pigs fed cellulose (control group). Higher number of hepatic apo B/E receptors in the PE and PSY groups were associated with lowering of LDL cholesterol. In addition, with high fat diets, plasma and hepatic triacylglycerol concentrations were lower in PE and PSY groups compared to control.^ The mechanisms of plasma lipid lowering were further explored in the high fat group. VLDL apo B secretion rates were slower and LDL fractional catabolic rates faster in guinea pigs fed PE or PSY compared to control animals. LDL particles isolated from guinea pigs fed PE or PSY were cholesteryl ester depleted, $\alpha$-tocopherol enriched and more resistant to oxidation than LDL isolated from the control group.^ Higher fecal bile acid concentrations which correlated with higher hepatic cholesterol 7 $\alpha$-hydroxylase activity, the regulatory enzyme of bile acid synthesis, were observed in guinea pigs fed PE, PSY and cholestyramine, a bile acid binding resin used as a positive control. Guinea pigs fed PE had higher concentrations of fecal neutral sterols than the control group. These results suggest that while the primary mechanisms of PE and PSY in the intestinal lumen appear to be related to interruption of the entero-hepatic circulation of bile acids, PE may also reduce cholesterol absorption.^ These studies demonstrated that PE and PSY not only reverse the hyperlipidemia induced by high fat/sucrose diets but they also decrease the susceptibility of LDL to oxidation, both factors associated with decreased risk of coronary heart disease. ^