Fecal sterol excretion in rats fed diets enriched in linoleic, α-linolenic, and eicosapentaenoic plus docosahexaenoic acid

The effects of feeding rats diets enriched in linoleic, alpha-linolenic, and eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA) on plasma and liver cholesterol as well as on fecal excretion of neutral sterols and bile acids were examined. Male Sprague-Dawley rats were divided into four groups (n=7) and were fed isocaloric, isocholesterolemic, nutritionally adequate diets containing 20% (w/w) fat for four weeks. The diets contained high amounts of either beef tallow, sunflower oil, linseed oil or fish oil to achieve diets rich in saturated fats, linoleic acid, alpha-linolenic, or EPA plus DHA respectively. Rat feces were collected during the last three days of the fourth week and blood and livers were obtained at the end of the feeding period. Fecal sterol excretion (neutral sterols plus bile acids) was significantly higher in rats fed the linoleic and the alpha-linolenic acid-rich diets compared to those fed the saturated fatty acid-rich diet. Higher sterol excretion rate in the linoleic acid diet group was found to be primarily due to higher excretion of plant sterols, whereas cholesterol excretion as such was rather lower than that with the saturated fatty acid diet. Higher sterol excretion rate following the feeding of the alpha-linolenic acid-rich diet was mainly due to higher excretion of bile acids, specifically lithocholic and beta-muricholic acid, Feeding of the linoleic acid-rich diet had no significant effect on bile acid excretion. EPA plus DHA, at the levels fed, had no effect on serum and liver cholesterol or on fecal excretion of total neutral sterol or bile acids, but significantly increased coprostanol excretion compared with that in the other groups. These data suggest that dietary linoleic acid reduces cholesterol excretion, which may partly be responsible for cholesterol accumulation in the hepatic tissue whereas n-3 fatty acids of plant (alpha-linolenic acid) and marine (EPA/DHA) origin increase fecal cholesterol excretion via different mechanisms, i.e., by increased conversion of cholesterol into bile acids.