Elevated plasma triglycerides are a risk factor for cardiovascular disease, and it is estimated that around a third of the population of the United states have hypertriglyceridaemia. Plasma triglycerides can be derived from the diet, because when fatty acids are absorbed, they are packaged into chylomicrons which enter the circulatory system via lymph vessels. Alternatively plasma triglycerides can be formed endogenously through the process of de novo lipogenesis. The quality and quantity of food in the diet is known to affect both of these mechanisms of elevating plasma triglycerides. For example, high amounts of fructose in the diet are known to cause elevated triglycerides because fructose is readily converted to fatty acids in the liver following ingestion. In contrast, omega 3 (n-3) fatty acids from fish are known to lower plasma triglycerides when given in higher concentrations perhaps by up-regulation of β-oxidation. .
Research has established that high concentrations (>3g/d) of fish oils are able to lower plasma triglycerides in those with elevated plasma concentrations. However, less is known about nutritionally more realistic doses of less than 1g/d. In order to establish the dose that might be beneficial, researchers1 compared the effects of two doses of fish oil supplements on the plasma triglycerides of 23 men and 3 postmenopausal women with hypertirglyceridaemia. The fish oil supplements consisted of 0.85 or 3.4g/d of eicosapentanoic acid (EPA, C20:5 (n-3)) and docosahexanoic acid (DHA, C22:6 (n-3)), administered in a double-blind, placebo controlled, randomised, cross over study for 8 weeks, followed by a 6 week washout. The low dose of fish oils (0.85g/d) did not significantly affect blood lipids. However, the high dose (3.4g/d) lowered plasma triglycerides by 27% compared to the placebo (173 mg/dL versus 237 mg/dL).
These results are interesting because they give some indication of the dose of n-3 fatty acids required to lower plasma triglycerides in hyperlipidaemic individuals. While the lower intake of fish oils did not significantly alter blood lipid levels, this may be a reflection of the short duration of the study. Lower doses may take longer to build up in plasma phospholipids and thus the beneficial effects may manifest more slowly. Interestingly, a 27% reduction in triglycerides is a large reduction, and any pharmaceutical drug claiming a similar benefit would be seen as a major benefit. The fact that the n-3 fatty acid supplementation was administered without side effects is something that should also be highlighted from this study. This study supports previous findings that show the greatest benefit of fish oils to those with the highest triglyceride levels. Evidence suggests that n-3 fish oil do not lower triglycerides in healthy individuals with normal levels.
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