| The question of how dietary fat is partitioned between the pathways of energy production and storage underlies several chronic disorders such as obesity, non-insulin dependent diabetes mellitus and cardiovascular disease. The goal of the present study was to integrate lipid metabolism by following the routes of various dietary fatty acids through energy utilization, transport in circulation, incorporation in adipose tissue, and conversion to other fatty acids. Four 13C-labelled fatty acids---oleate (9 cis-18:1), alpha-linolenate (ALA, 18:3n-3), elaidate (9 trans-18:1) and linoleate (LA, 18:2n-6), were administered as a single oral bolus to six healthy women. Samples were collected over 168 h. 13C in breath CO 2 and in plasma triglycerides (TG), phospholipids (PL), cholesteryl esters (CE), and free fatty acids (FFA) were analysed using isotope ratio mass spectrometry and the area under the isotope enrichment curve was determined. Adipose tissue biopsies were obtained at 6 h, 24 h, and 168 h after dosing.;Selective incorporation of tracer LA into plasma PL and CE occurred, accompanied by lower oxidation of 13C LA, as compared to elaidate, oleate and ALA. In plasma TG, enrichment was in the order of elaidate > oleate > ALA. Elaidate was a poor substrate for cholesterol esterification. Enrichment in the desaturated and elongated products of LA and ALA was observed, but in low amounts. Enrichment in adipose tissue was observed as early as +6 h after dosing with ALA, elaidate and LA, and was still present at 168 h. Individuals with higher LA levels in plasma PL oxidised more of 13C LA and elaidate, implicating a relationship of high LA feeding to increased fatty acid oxidation.;Although elaidate was highly oxidised, it also incorporated the highest in TG and the lowest in CE, which may relate to its hyperlipidemic effect. LA, although less oxidised, was incorporated into plasma PL and CE to a greater extent, indicating a preference for lipid membrane incorporation rather than oxidation. These metabolic differences can ultimately lead to an explanation of the differential health effects of these dietary fatty acids. |
