Journal Name:
Eur. J. Clin. Nutr.
Article Title:
Effects of dietary fatty acids on the composition and oxidizability of low-density lipoprotein.
Date Written:
2002
Volume:
56
Number:
1
Page:
72
Author(s):
Kratz, M.; Cullen, P.; Kannenberg, F.; Kassner, A.; Fobker, M.; Abuja, P.M.
Article:
Dietary fat may influence the risk of coronary heart disease by several mechanisms including effects on the susceptibility of LDL to oxidation which, once modified, are taken up by macrophages, which in turn become lipid-laden foam cells. It might be assumed that diets rich in saturated fatty acids (SFA) would lead to the production of LDL that are relatively resistant to oxidation, while the susceptibility of LDL to oxidation can be expected to increase with an increasing amount of unsaturated fatty acids in the diet. This study was designed to test the following: (1) what are the effects of diets containing different amounts of MUFA, n-6-PUFA and n-3-PUFA on LDL oxidation? (2) Do dietary fatty acids differ in their propensity for incorporation into LDL and hence in their ability to influence the susceptibility of LDL to oxidation? and (3) Do dietary MUFA result in reduced susceptibility of LDL to oxidation simply because they displace PUFA, or are there other protective mechanisms? Fifty eight healthy young volunteers completed the study. The participants received a 2-week wash-in diet rich in SFA followed by diets rich in refined olive oil, rapeseed (canola) oil or sunflower oil for 4 weeks. Intakes of vitamin E and other antioxidants did not differ significantly between the diets.
At the end of the study, LDL oxidizability was lowest in the olive oil group (lag time: 72.6 min), intermediate in the rapeseed oil group (68.2 min) and highest in the sunflower oil group (60.4 min). Despite wide variations in SFA intake, the SFA content of LDL was not statistically different between the four diets (25.8 – 28.5% of LDL fatty acids). PUFA (43.5% – 60.5% of LDL fatty acids) and MUFA content of LDL (13.7 – 29.1% of LDL fatty acids) showed a wider variability dependent on diet. *In this study, n-6-PUFA lowered LDL-cholesterol more than MUFA and had a greater HDL-cholesterol lowering effect. Thus, their overall effect on lipoprotein metabolism is considered to be similar. Compared to PUFA-rich diets, diets rich in MUFA lead to LDL that is more resistant to oxidation. n-3 PUFA in large amounts (of about 20 g per day) or in the context of a diet rich in PUFA increase the susceptibility of LDL to oxidation. However, intake of n-3 PUFA is not associated with an increase in the urinary isoprostane excretion, a good measure of in vivo lipid peroxidation. MUFA-rich diets lead to LDL that is less oxidizable than that found on a diet rich in PUFA, as evidenced here for LDL oxidizability, ie lag time, rate of propagation and maximum amount of conjugated dienes. On the MUFA-rich diets the oxidizability of LDL was lower even than that on the initial SFA-rich diet.
The olive oil diet led to an increase in LDL oleic acid and a concomitant decrease in LDL linoleic acid, thereby reducing the susceptibility of the LDL particles to oxidation compared to the SFA-rich diet. The canola/rapeseed oil diet led to enrichment of LDL with the n-3 PUFAs alpha-linolenic acid and eicosapentaenoic acid (while linoleic acid remained unchanged), and a reduced susceptibility of LDL to oxidation. Here the increase in oleic acid more than compensated for the increase in highly oxidizable n-3 PUFA found within LDL on this diet. This implies that an increase in LDL oleic acid content reduces LDL in vitro oxidizability independently of a displacement of PUFA from LDL. Furthermore, n- 3 PUFA in moderate amounts appear not to exert adverse effects with regard to LDL oxidation when provided in the context of a diet rich in MUFA such as canola oil.
In conclusion, in the healthy persons in this study, MUFA were more beneficial than SFA and n-6 PUFA in terms of effects on LDL oxidizability. They also prevented highly unsaturated n-3 fatty acids from exerting a potentially negative effect in this regard. These results support recommendations to increase the ratio of MUFA to n-6 PUFA in the diet and to include canola oil where possible to protect against CHD.
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