The cholesterol-lowering effect of guar gum in rats is not accompanied by an interruption of bile acid cycling

A viscous hydrocolloid (guar gum, GC; 2.5% of the diet) or a steroid sequestrant (cholestyramine; 0.5% of the diet) was included in semipurified diets containing 0.2% cholesterol to compare the cholesterol-lowering effects of each agent in rats. In the present model, CC significantly lowered plasma cholesterol (-25%), especially in the density <1.040;kg/L fraction, whereas cholestyramine was less potent. Bile acid fecal excretion significantly increased only in rats fed cholestyramine, similar to the cecal bile acid pool; the biliary bile acid secretion was accelerated by GG, but not their fecal excretion, whereas GC effectively enhanced neutral sterol excretion. As a result, the total steroid balance (+13 mu mol/d in the control) was shifted toward negative values in rats fed the CG or cholestyramine diets (-27 or -50 mu mol/d, respectively). Both agents induced liver 3-hydroxy-3-methylglutaryl-CoA reductase, but cholestyramine was more potent than CC in this respect. The present data suggest that, at a relative low dose in the diet, GC may be more effective than cholestyramine in lowering plasma cholesterol by impairing cholesterol absorption and by accelerating the small intestine/liver cycling of bile acids, which is interestingly, accompanied by reduction of bile acid concentration in the large intestine.