Incorporation of the dietary trans fatty acid (C18:1) into the serum lipids, the serum lipoproteins and adipose tissue

Abstract

Two diets, identical except for differences in trans and cis fatty acids, were fed to rabbits in order to evaluate the effects of dietary trans fatty acids on the fatty acid composition of serum lipids, lipoproteins and adipose tissue. The animals were first starved to deplete adipose tissue stores and then were red a diet containing 15% of the calories as C18:1 trans fatty acid (elaidic acid). A second group received a diet containing an equivalent amount of C18:1 cis fatty acid (oleic acid). A third group of animals, the control group, was fed only the baseline low fat rabbit chow. Dietary trans fatty acid was incorporated into all serum lipid and lipoprotein fractions and into the adipose tissue. In the serum the triglycerides contained the greatest amount of trans fatty acid followed by the phospholipids with cholesterol esters containing the least. The trans fatty acids of the phospholipids and cholesterol esters were distributed equally among the lipoprotein fractions, but the triglycerides of high density lipoproteins contained less trans fatty acids than did the triglycerides of other lipoproteins. Adipose tissue developed a high content of C18:1 trans fatty acid (21.7%), apparently at the expense of C18:1 cis fatty acid. In addition to the incorporation of C18:1 trans fatty acid, the content of other fatty acids, including C18:2 and the total of C18:1 cis and trans, was influenced by the substitution of dietary trans for cis fatty acids. The serum phospholipids of the trans-fed rabbits contained more C18:2 than the phospholipids of the cis-fed rabbits. The serum cholesterol esters of the trans-fed rabbits contained more C18:2 and a smaller total of C18:1 (cis puls trans) than the cholesterol esters of the cis-fed rabbits. These differences indicated that C18:1 trans fatty acid was not necessarily the metabolic equivalent of 18:1 cis fatty acid. These results suggested that dietary trans fatty acids which are contained in hydrogenated margarines, shortenings and oils of the human diet are readily incorporated into the lipids of the body including membranous structures such as lipoproteins.