Regulation of plasma and hepatic lipids by dietary fatty acids: Effects of oleic, elaidic and palmitic acids

This study compares the effects of dietary oleic acid (OA), palmitic acid (PA), and trans fatty acids (TFA) on lipid metabolism in rabbits. Animals were fed semipurified diets in which a fifth of the fat intake (6% total energy) was either OA, PA, or TFA in the presence and absence of dietary cholesterol (0.2% w/w). After 10-12 weeks of feeding the cholesterol-free diets, there were no significant differences in plasma total cholesterol or triacylglycerol concentrations between groups. However, there was an increase in the cholesterol concentration of the lower density lipoproteins in rabbits fed the TFA diet compared with their OA-and PA-fed counterparts. The addition of dietary cholesterol had no effect on plasma lipids, however hepatic cholesterol concentrations were lower in animals fed the PA diet compared with those fed the OA diet (p<0.05), mainly due to a reduction in cholesteryl ester concentration (p<0.05). Despite these changes, hepatic low density lipoprotein (LDL)receptor activity was not affected by diet. Palmitic and linoleic acids comprised similar proportions in the OA and TFA diets, however the proportion of hepatic phospholipid fatty acids as palmitic acid was lower (p<0.0001) while linoleic acid was higher (p<0.01) in animals fed TFA compared with those fed OA. These findings indicate that in rabbits fed dietary cholesterol (0.2%) TFA do not negatively impact on plasma lipids compared with either OA or PA. Also, increased esterification of TFA and linoleic acid to phospholipids at the expense of palmitic acid in animals fed TFA suggests that feeding TFA may result in cellular membranes with altered physical characteristics.