Submitted to: Lipids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/19/2003
Publication Date: 3/1/2004
Citation: Emken, E.A., Adlof, R.O., Duval, S.M., Shane, J.M., Walker, P.M., Becker, C. 2004. Effect of triacylglycerol structure on absorption and metabolism of isotope labeled palmitic and linoleic acid by humans. Lipids. 39:1-8. Interpretive Summary: The structure of dietary fats has been suggested as possible risk factors associated with heart disease. Until now, there has been no clear evidence in humans to disprove or support this suggestion. For this study, fats of different structures and tagged with stable isotopes were prepared and fed to humans. The isotope tags let scientists follow and measure the uptake and turnover of the different fats. More importantly, this study demonstrated that the human body can re-tailor the fats we eat to form the structures it requires. The structure of the fats we eat is therefore unlikely to be a heart disease risk factor because fat structures have little influence on fat uptake and breakdown in adult men. The results of this research will help in the development/formulation of nutritional guidelines and heart disease risk factors for both animal and vegetable fats.
Technical Abstract: The effect of dietary triacylglycerol (TAG) structure and fatty acid acyl TAG position on palmitic and linoleic acid metabolism was investigated in four middle-age male subjects fed diets supplemented with 61 g\d of native lard (NL) or randomized lard (RL) for 28 days. At the end of the diet period, two RL diet subjects were each fed 8.5 g of 1,3-tetradeuteriopalmitoyl-2-dideuteriolinoleoyl-rac-glycerol (P4L2P4) and two NL diet subjects were each fed a mixture containing 7.75 g of 1,3-dideuteriolinoleoyl-2-tetradeuteriopalmitoyl-rac-glycerol (L2P4L2) and 4.25 g of 1,3-hexadeuteriopalmitoyl-2-tetradeuteriolinoleoyl-rac-glycerol (P6L4P6). Blood samples were drawn over a 2-day period and methyl esters of the isolated plasma lipids were analyzed by GC-MS. All 2H-fatty acids were equally well absorbed by all subjects. The 2H-fatty acids at the 2-acyl position of the fed triacylglycerols were 85 ± 4.6% retained after absorption but substantial migration of 2H-16:0 (31.2 ± 8.6%) from the sn-2 acyl position to the sn-1,3 position and 2H-18:2n-6 (52.8 ± 6.4%) from the sn-1,3 position to the sn-2 position of chylomicron TAG occurred after initial absorption. Incorporation and turnover of the 2H-fatty acids in chylomicron TAG, plasma TAG and CE was not influenced by diet or acyl TAG position. Incorporation of 2H-16:0 fed as sn-2 TAG in PC-1 was 1.7 times higher than 2H-16:0 fed as sn-1,3 TAG. Dietary acyl TAG position did not influence 18:2n-6 incorporation in PC. The concentration of 2H-20:4n-6 in plasma PC from subjects fed the RL diet was 1.5 times higher than for subjects fed the NL diet and suggests that diets containing 16:0 located at the sn-2 TAG position inhibit 20:4n-6 accretion in plasma PC. Overall, the results from this isotope tracer study show that dietary TAG structure has some influence on 16:0 and 18:2n-6 metabolism and that extensive modification of the chylomicron TAG structure reduces the metabolic and physiological effects of TAG structures.