Raising intestinal contents viscosity leads to greater excretion of neutral steroids but not bile acids in hamsters and rats

To examine the effect of intestinal contents viscosity on fecal steroid excretion independent of colonic fermentation, hamsters and rats were fed cholesterol-containing diets containing either cellulose or different viscosity grades of hydroxypropyl methylcellulose (HPMC), a non-fermentable fiber, as the dietary fiber source. HPMC feeding relative to cellulose significantly lowered plasma cholesterol in hamsters and liver cholesterol in rats. Fecal neutral steroid excretion was significantly greater in both species consuming HPMC compared to cellulose. Fecal bile acid excretion was not altered in hamsters, but was reduced in rats fed HPMC compared to cellulose. Thus, greater intestinal contents supernatant viscosity results in reduced plasma (hamster) or liver (rat) cholesterol and greater neutral steroid excretion, whereas bile acid excretion is unaffected or reduced. This suggests that viscosity is the principal characteristic of dietary fiber responsible for cholesterol lowering, and that this effect is due to increased excretion of cholesterol from the body.