The metabolic syndrome is characterised by insulin resistance and this results in a number of metabolic abnormalities. One such abnormality is an increase in the de novo lipogenesis pathway of the liver. The de novo lipogenesis pathway is involved with the synthesis of new fatty acids and its key regulatory control enzymes are under allosteric control by insulin. High levels of insulin increase flux through the pathway and as a result the fatty acid synthesis rates increase. The synthesis of triglycerides from the resultant fatty acids is also under the control of insulin and so high levels of insulin characterising the metabolic syndrome result in high levels of circulating fatty acids in the fasting state. These fatty acids are transported from the liver to the circulation in the very low density lipoprotein (VLDL) particle and as the triglycerides are removed the density of the lipoprotein changes and it becomes the low density lipoprotein (LDL) particle. Those with metabolic syndrome therefore also often have high levels of LDL.
A number of nutrients and plant metabolites have been shown to be effective at lowering the circulating levels of lipoproteins in those with raised levels. In particular, the fish oil fatty acid eicosapentaenoic and (EPA, C20:5 (n-3)) and docosahexaenoic acid (DHA, C22:6 (n-3)) have been shown to be effective at lowering plasma levels of triglycerides, and a group of phytonutrients, the sterols, have been shown to be effective at lowering plasma levels of LDL cholesterol. Those with raised levels of both VLDL and LDL may therefore benefit from concomitant supplementation with sterols and fish oils. For example1, subjects with hypercholesterolaemia were fed either a control spread with no fish oils or sterols, or one of a number of spreads containing 2.5 grams of plant sterols and supplying 0, 0.9, 1.3 or 1.8 grams per day of fish oils. Compared to the control the fish oil spreads resulted in a dose related reduction in plasma triglycerides that varied from between 9.3 and 16.2 % of control values.
The sterol consumption also caused reductions in plasma LDL concentrations that varied from 11.5 to 14.7 % of the control group. Therefore spreads containing fish oils and plant sterols may be beneficial to reversing raised levels of lipoproteins in hypercholesterolemic individuals. In this study the subjects consumed spreads that were part of the diet. However, the incorporation of fish oils in spreads is problematic because the fatty acid are delicate and easily subject to oxidation. A far superior way to take fish oils is in the form of whole fish, and the triglyceride lowering effects of fish oils can be obtained by consuming fatty fish, such as tuna, mackerel, salmon or trout, 2 to 3 times per week. Plant sterols in studies are often administered as supplements or in spread as this makes the dosage easy to control. However plants generally contain sterols, and so high plant diets have high amounts of sterols. This may explain some of the plasma lipid lowering effects of traditional diets such as the mediterranean diet.
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