Positive Health Online

Abstract

WAGNER and colleagues, Institute of Nutritional Sciences, University of Vienna, Austria, karl-heinz.wagner@univie.ac.at, investigated the effects of dietary supplementation with oil rich in polyunsaturated fatty acids (PUFAs) in comparison with dietary supplementation with an oil mixture rich in saturated (SFAs), monounsaturated (MUFAs) and polyunsaturated fatty acids on blood fatty acid levels.

Background

Results from previous studies comparing effects of SFAs, MUFAs and PUFAs and their combinations have been contradictory.

Methodology

This was a double-blind, randomized, comparative, cross-over design study in 28 healthy male non-smokers aged 19-31 years. Dietary supplementation with two types of oils were compared: 1) an olive oil/sunflower oil mixture containing a high level of oleic acid and a moderate level of PUFAs (ratios of SFAs:MUFAs:PUFAs = 14:69:17) ('M-rich') ; 2) a single PUFA-rich corn oil (SFAs:MUFAs:PUFAs = 13:33:54) ('P-rich') . The subjects entered a 2-week baseline period during which they consumed a mixed balanced diet (average calories 11.6 MJ, average fat 105 g/day). This was followed by a 2-week study period when they consumed a diet supplemented with either the P-rich oil (80 g corn oil/day) or the M-rich oil (68 g olive oil + 12 g sunflower oil/day) as the main fat source. Subjects were then crossed over to the opposite oil- supplemented diet for a further 2 weeks . Dietary compliance was confirmed by measuring fatty acid compositions of plasma low-density lipoproteins (LDLs) and levels of alpha- and gamma-tocopherol in plasma and plasma LDLs. The researchers investigated the effects of the dietary supplementations on plasma levels of LDL-cholesterol, high density lipoproteins (HDLs), HDL-cholesterol, very low-density lipoprotein (VLDL)-triglycerides, total triglycerides and total cholesterol.

Results

There were significant changes in plasma LDL and tocopherols and LDL-tocopherols and significant changes in the average ratio of oleic to linoleic acids in LDL, confirming that the dietary lipids were well incorporated . The P-rich diet significantly reduced LDL-cholesterol after the first 2-week study period and showed a similar but less pronounced (non-significant) trend after the cross-over study period. The P-rich diet reduced total triglyceride levels and VLDL-triglyceride levels to a significantly greater extent than the M-rich diet after the first 2-week study period and similarly reduced total cholesterol levels after the cross-over study period. Neither diet affected total HDL and HDL-cholesterol levels.

Conclusion

The PUFA-rich diet had a greater influence on lipoprotein metabolism than the MUFA-rich diet . The cholesterol-lowering effect of the PUFA-rich diet is likely to be related to its high content of unsaponifiable (non-hydrolysable) substances, mainly phytosterols in the corn oil .

References

Wagner KH et al. Impact of diets containing corn oil or olive/sunflower oil mixture on the human plasma and lipoprotein lipid metabolism. European Journal of Nutrition 40 (4): 161-7. Aug 2001.