Dietary beef tallow alters the fatty acid profiles of bile and liver membranes, but not secretion of cholesterol in bile

Abstract

To test the hypothesis that type and amount of dietary fat has a regulatory effect on secretion of cholesterol in bile, young growing pigs were fed diets containing either 20% or 40% of energy as primarily either beef tallow or soybean oil or as a 50:50 (wt:wt) blend of tallow and soybean oil. After week 6, pigs were injected with autologous low-density lipoproteins containing 3H-cholesterol. Serial bile samples were collected for 24 hours; then tissues were collected. Amount of tallow in dietary fat correlated positively (P < 0.05) with amounts of palmitoleic and oleic and negatively with linoleic and linolenic fatty acids in biliary phospholipids. In addition, amount of tallow in dietary fat correlated positively with amounts of myristic, palmitoleic and oleic acids but negatively with stearic acid in membranes of liver. Composition of dietary fat, however, did not affect concentration or daily secretion of cholesterol, bile acids or phospholipids in bile. Furthermore, secretion of 3H-cholesterol as biliary cholesterol or bile acids was not affected by type or amount of dietary fat. Concentration of cholesterol in liver tended to be greater in pigs fed diets containing tallow (P<0.10); no differences in cholesterol concentrations, however, were seen in aorta, heart, skeletal muscle, or gastrointestinal tract. Percentage of injected 3H-cholesterol was greater (P<0.001) in perirenal adipose tissue from pigs fed diets containing soy oil than from pigs fed diets containing tallow. There were no significant differences (P<0.05) seen in percentage of injected 3H-cholesterol deposition in several other organs. In summary, type of dietary fat altered fatty acid composition of biliary phospholipids and liver membranes but had no effect on cholesterol secretion into bile and no major effects on cholesterol distribution in major organs of young pigs.