Influence of dietary fat on the concentration of long-chain unsaturated fatty acid families in rat tissues.

The relative concentration of long-chain unsaturated fatty acids (chain length C(20) and greater) of the (n - 6), (n - 7), and (n - 9) families in the cholesteryl esters and phospholipids of rat adrenals, liver, heart, and plasma lipoproteins was measured after the feeding of hydrogenated fat, milk fat, beef tallow, corn oil, and fat-free diets. Barely optimal levels of dietary linoleate were found to result in the same order of concentration of the (n - 6) series of fatty acids as was obtained with excess dietary linoleate. The linoleate-poor or deficient diets-hydrogenated fat and fat-free diets-gave almost identical levels and trends with respect to the concentration of the (n - 9) and (n - 7) series of acids. With these two diets, the concentrations of the total (n - 9) long-chain acids were several times greater than the amounts obtained by feeding either the linoleate-rich diet or the barely linoleate-adequate diets. It is concluded from the results that the linoleate-deficient nature of the hydrogenated fat, rather than its high content of trans acids, would explain the high tendency of this fat to induce the accumulation of long-chain (n - 9) fatty acids in the cholesteryl esters and phospholipids of the tissues studied.