DIETARY LINOLEIC-ACID INFLUENCES DESATURATION AND ACYLATION OF DEUTERIUM-LABELED LINOLEIC AND LINOLENIC ACIDS IN YOUNG-ADULT MALES

The purpose of this study was to investigate the effect of dietary lin oleic acid (18:2(n - 6)) on the conversion of 18:2(n - 6) and 18:3(n - 3) to their respective n - 6 and n - 3 metabolites; to compare the in corporation of these fatty acids into human plasma lipids; to evaluate the importance of dietary 18:3(n - 3) as a precursor for the biosynth esis of long-chain length n - 3 fatty acids. The approach used was to feed young adult male subjects (n = 7) diets containing 2 levels of li noleic acid (SAT diet, 15 g/day; PUFA diet, 30 g/day) for 12 days. A m ixture of triacylglycerols containing deuterated linolenic (18:3(n - 3 )) and linoleic (18:2(n - 6)) acids was fed and blood samples were dra wn over a 48 h period. Concentrations of deuterated 18:3(n - 3) in pla sma total lipid ranged from 309.2 to 606.4 mu g/ml and concentrations of 18:2(n - 6) ranged from 949.2 to 1743.3 mu g/ml. The sum of the deu terated n - 3 long-chain length fatty acid metabolites in plasma total lipid were 116 +/- 4.3 mu g/ml (SAT diet) and 41.6 +/- 12.4 mu g/ml ( PUFA diet). The total deuterated n - 6 fatty acid metabolites were 34. 6 +/- 12.2 mu g/ml (SAT diet) and 9.8 +/- 5.9 mu g/ml (PUFA diet). The total percent conversion of deuterated 18:3(n - 3) to n - 3 fatty aci d metabolites and deuterated 18:2(n - 6) to n - 6 fatty acid metabolit es were 11-18.5% and 1.0-2.2%, respectively. The percentages for deute rated 20:5(n - 3), 22:5(n - 3) and 22:6(n - 3) (6.0%, 3.5%, and 3.8%) were much higher than for 20:3(n - 6) and 20:4(n - 6) (0.9% and 0.5%). Overall, conversion of deuterated 18:3(n - 3) and 18:2(n - 6) was red uced by 40-54% when dietary intake of 18:2(n - 6) was increased from 1 5 to 30 g/day. Comparison of the deuterated 18:3(n - 3) and 18:2(n - 6 ) data for plasma triacylglycerol and phosphatidylcholine (PC) indicat ed that 18:2(n - 6) was preferentially incorporated into PC. Dietary 1 8:2(n - 6) intake did not alter acyltransferase selectivity but activi ty was reduced when 18:2(n - 6) intake was increased. Based on these r esults, conversion of the 18:3(n - 3) in the US diet (2 g) is estimate d to provide 75-85% of the long-chain length n - 3 fatty acids needed to meet daily requirements for some (but not all) adults.