The effects of guar gum and its enzyme hydrolysate as well as fructooligosaccharide on lipid metabolism were compared in rats fed high-fat diets employing lard or palm oil as dietary fat (25% in the diets). Guar gum and the enzyme hydrolysate greatly increased cecal volatile fatty acid contents to a similar extent. Fructooligosaccharide also increased the variable but to a lesser extent. Not only guar gum but also the hydrolysate and the oligosaccharide reduced serum cholesterol levels irrespective of dietary fat sources but to a lesser extent. The triglyceride-lowering effects of the hydrolysate and the oligosaccharide were comparable to that of guar gum. Although guar gum enzyme hydrolysate and fructooligosaccharide doubled the biliary bile acid excretion, these materials only slightly increased the activities of hepatic enzymes of cholesterol and bile acid synthesis. Guar gum and its hydrolysate suppressed 3-hydroxy-3-methylglutaryl-coenzyme A reductase activities in the ileum to one half the control value in the experiment where dietary fat was lard. The highly polymeric structure does not appear to be a prerequisite for nonabsorbable carbohydrate to alter lipid metabolism at least in rats fed high-fat diets.