Fatty acid composition of an oral load affects chylomicron size in human subjects

Abstract

HDL-phospholipids are determinants in reverse cholesterol transport. They are mostly derived from triacylglycerol (TG)-rich lipoproteins. Chylomicron size is important, therefore, because it is related to the ratio surface phospholipids: core TG and, thus, determines the availability of postprandial phospholipids for transfer to HDL. Eleven healthy young women each ingested four different fat loads supplemented with retinyl palmitate and containing 60 g sunflower oil (SO), oleicsunflower oil (OSO), mixed oil (MO; (g/kg) linoleic acid 480, oleic acid 380, linolenic acid 13) or beef tallow (BT). At the peak of TG absorption for all loads (4 h) chylomicron diameters, determined by agarose-gel filtration, were larger after SO compared with OSO (i><0-05) and BT (i>=006) and after MO compared with BT (P < 0-05). At 6 h chylomicron size was larger after the vegetable oils compared with BT (P < 0 05 in each case). After each fat load chylomicron size decreased at 6 and 8h compared with that at 4h (P<005) except for OSO. Retinyl ester and TG concentrations were lower in chylomicrons after BT than after the other fats but not in the chylomicron-free serum (containing chylomicron remnants), suggesting absorption in the form of very small particles. Compared with the fasting value, the concentration of the Svedberg unit of flotation 20-400 fraction, which contains VLDL and chylomicron remnants, was lower 8 h after MO, the only fat to contain significant amounts of linolenic acid. We conclude that chylomicron size is dependent on the fatty acid composition of ingested fats and the time-course of digestion, being larger for polyunsaturated fatty acid-rich fats and in the early phase of digestion. On the basis of retinyl ester concentration there were no differences between fats in chylomicron-remnant clearance.

Methodology for studying postprandial lipid metabolism

“…More recently, studies that have measured changes in different lipoprotein subfractions have revealed important differences with lipemic responses being of the order saturated fatty acid (SFA)4monounsaturated fatty acid (MUFA)4PUFA (Jackson et al, 2002a, b;Jackson et al, 2005). It is important to note that the physicochemical characteristics of the meal-fat mixture, linked to the fatty acid composition, could be a highly determinant of the rate of digestion and absorption, thus on the extent and/or kinetic of the postprandial lipid response (Sakr et al, 1997;Armand et al, 1999). N-3 PUFAs can lower the postprandial triglyceride response if sufficient amount is present within the test meal (Zampelas et al, 1994a), but levels used were far greater than those which would be consumed by most populations.…”

“…Thus, lipid moieties are organized in different kind of complex structures (emulsified droplets with different compositions and sizes, multilamelar structures, vesicles) that will determine the rate of fat digestion by gut lipases (Armand et al, 1996(Armand et al, , 1999. This can affect the rate of gastric emptying as well as kinetics of postprandial occurrence of chylomicrons in the circulation (Sakr et al, 1997;Armand et al, 1999). Great care should be taken on this aspect in designing test meals and postprandial studies.…”

ACTH reduces the rise in ApoB-48 levels after fat intake

“…Rather, lipid transfer to the plasma compartment seemed accelerated, probably due to glucocorticoid effects on the GI motor complex (27,28).This suggests that fewer but larger, i.e. fat-richer, chylomicrons are generated after ACTH administration (29,30). In fact, the observation that dietary markers did not display similar postprandial plasma patterns as ApoB-48 is consistent with the view that the lipid-lowering effect of ACTH is due to direct inhibition of ApoB synthesis, since the decreased secretion of lipoproteins does not seem to result from decreased lipid availability.…”

Gender influence on plasma triacylglycerol response to meals with different monounsaturated and saturated fatty acid content

“…Studies by Thomsen et al (1999Thomsen et al ( , 2003 reported lower plasma TAG levels after consumption of a high-MUFA meal compared with a high-saturated fatty acids (SFA) meal. In contrast, other studies have shown that meals or fat emulsions rich in MUFA produce higher postprandial TAG compared with SFA (Higashi et al, 1997;Sakr et al, 1997;Mekki et al, 2002). Finally, other studies have demonstrated that replacement of SFA with MUFA in acute test meals does not influence postprandial plasma TAG metabolism Jackson et al, 1999Jackson et al, , 2002.…”