INFLUENCE OF DIETARY RETROGRADED STARCH ON THE METABOLISM OF NEUTRAL STEROIDS AND BILE-ACIDS IN RATS

Diets enriched in retrograded amylose (RS,) have been shown to lower s erum cholesterol concentrations in rats, The possibility was tested th at this hypocholesterolaemic effect of RS(3) is caused by an increase in excretion of neutral steroids and/or bile acids, Six groups of ten rats were fed on purified diets containing either 12 or 140 g RS(3)/kg solid ingredients with and without added cholesterol (5 g/kg), Low-RS (3) diets, with and without added cholesterol, to which the bile-acid- binding resin cholestyramine (20 g/kg) was added, were used as referen ce, The high-RS(3) diets v. the low-RS(3) diets tended to reduce the i ncrease in the total serum cholesterol concentration during the course of the experiment (P = 0.067), decreased serum triacylglycerol concen trations, raised total neutral steroids and total bile acids in caecal contents and faecal excretion of total bile acids, but lowered faecal excretion of neutral steroids, In addition, the serum concentration o f total 3 alpha-bile acids was markedly raised by the high-RS(3) diets , The high-RS(3) diets raised the faecal excretion of lithocholic and muricholic acids, but lowered that of hyodeoxycholic acid, and increas ed the caecal amounts of Lithocholic, ursodeoxycholic, beta-muricholic and omega-muricholic acids, Apart from the stimulation of faecal bile acids excretion, the effects of cholestyramine on bile acid metabolis m differed at various points from those of RS(3). Cholesterol feeding had predictable effects on cholesterol metabolism and led to greater e levating effects of RS(3) on the faecal and caecal amounts of murichol ic acids, The results suggest that the serum-cholesterol-lowering effe ct of high-RS(3) diets may be explained by an increased influx of neut ral steroids and bile acids into the caecum, and increased faecal excr etion of bile acids, and/or by an altered intestinal bile acid profile .