Effect of triacylglycerol structure on absorption and metabolism of isotope‐labeled palmitic and linoleic acids by humans

Abstract

The effect of dietary TAG structure and fatty acid acyl TAG position on palmitic and linoleic acid metabolism was investigated in four middle-aged male subjects. The study design consisted of feeding diets containing 61 g/d of native lard (NL) or randomized lard (RL) for 28 d. Subjects then received an oral dose of either 1,3-tetradeuteriopalmitoyl-2-dideuteriolinoleoyl-rac-glycerol or a mixture of 1,3-dideuteriolinoleoyl-2-tetradeuteriopalmitoyl-rac-glycerol and 1,3-hexadeuteriopalmitoyl-2-tetradeuteriolinoleoyl-rac-glycerol. Methyl esters of plasma lipids isolated from blood samples drawn over a 2-d period were analyzed by GC-MS. Results showed that absorption of the 2H-fatty acids (2H-FA) was not influenced by TAG position. The 2H-FA at the 2-acyl TAG position were 85+/-4.6% retained after absorption. Substantial migration of 2H-16:0 (31.2+/-8.6%) from the sn-2 TAG 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 and indicates the presence of a previously unrecognized isomerization mechanism. Incorporation and turnover of the 2H-FA in chylomicron TAG, plasma TAG, and plasma cholesterol esters were not influenced by TAG acyl position. Accretion of 2H-16:0 from the sn-2 TAG position in 1-acylphosphatidylcholine was 1.7 times higher than 2H-16:0 from the sn-1,3 TAG positions. Acyl TAG position did not influence 2H-18:2n-6 incorporation in PC. The concentration of 2H-18:2n-6-derived 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 this result suggests that diets containing 16:0 located at the sn-2 TAG position may inhibit 20:4n-6 synthesis. The overall conclusion is that selective rearrangement of chylomicron TAG structures diminishes but does not totally eliminate the metabolic and physiological effects of dietary TAG structure.

Regio-distribution of stearic acid is not conserved in chylomicrons after ingestion of randomised, stearic acid-rich fat in a single meal

“…This is in conflict with some [12,13,23,27] but not all [10,28] earlier investigations using randomised SFA-rich fats. Our results are in line with those of Emken et al [29], who, using isotope-labeled TAGs, found that the other common SFA, palmitic acid, also undergoes substantial isomerisation after absorption, whereas the position is conserved with polyunsaturated linoleic acid. The anticipated increased fecal stearic acid losses from the sn-2 position [10,30] can be excluded as only marginal amounts were found in the feces [14].…”

Short Chain Saturated Fatty Acids Decrease Circulating Cholesterol and Increase Tissue PUFA Content in the Rat

“…However, we have also to take into account that myristic acid is mainly in the sn-2 position in dairy TAG of the butterfat diet, whereas it is equally distributed in the 3 positions in the synthetic saturated TAG of the two other saturated fat diets (saturates and trimyristin diets) [37]. It has been suggested that fatty acids in the sn-2 position are better absorbed in enterocytes [38], but there are still controversies about the real physiological impact of fatty acids when located in the sn-2 position [39,40]. In our study, when analyzing the effect of the 3 diets containing 10-12 mol% myristic acid (butterfat, saturates and trimyristin), myristic acid was found significantly higher in adipose tissue of the rats fed the butterfat diet ( Table 3), suggesting that myristic acid in sn-2 position is indeed better absorbed or better stored.…”

Human Studies Using Isotope Labeled Fatty Acids: Answered and Unanswered Questions

“…However, the conclusion from the data shown for percent conversion would be that diet did not have an Fig. 8 Effect of triglyceride acyl position on conversion of 2 H-18:2n-6 to 2 H-20:4n-6 in male subjects pre-fed native and randomized lard diets 16) .…”