Dietary fibers III. Effects of chronic intake on cholesterol absorption and metabolism in the rat

Abstract

Rats were fed for 6 weeks on defined diets containing 15% levels of wheat bran, alfalfa meal, a yeast cell wall glycan, cellulose and pectin, or 2% cholestyramine. Intestinal transit times were determined on all animals after 5 weeks on diet. Lymphatic absorption of a test dose of labeled cholesterol and triglyceride, introduced intraduodenally, was determined on all animals. Additional analyses included plasma triglycerides and cholesterol, hepatic triglycerides, cholesterol and phospholipids, and hepatic 7α-hydrolylase activities. Binding of bile salts and cholesterol by each of the test materials (except pectin) was determined in vitro. Of the various test materials studied, cholestyramine, pectin, alfalfa, and cellulose feeding all resulted in significant reductions of lymphatic absorption of both cholesterol and triglycerides, while the effect of wheat bran was marginal and the yeast glycan was without effect. Only wheat bran and cellulose diets significantly reduced transit times, and neither dietary component was effective in bile acid sequestration. In contrast, cholestyramine and alfalfa showed bile acid binding activity but no effects on transit time. Since the basic diet did not induce elevations in plasma lipids, none of the test materials had significant effects on either plasma cholesterol or triglycerides. However, those test materials that were effective in interfering with intestinal lipid absorption also resulted in significant depressions of hepatic triglycerides and increases in hepatic phospholipids. The present results suggest a direct effect of certain dietary fibers or fiber components on intestinal absorption of lipids by mechanisms involving either binding of intraluminal bile salts or by interference in bulk phase diffusion of the lipids. In addition, indirect effects of these same test materials are also evident in terms of alterations of hepatic lipids and/or lipoprotein metabolism.