Fatty fish and their oils have been shown to be beneficial to health, particularly with regard cardiovascular disease. Fish oils contain the omega-3 fatty acids eicosapentanoic acid (EPA, C20:5 (n-3)) and docosahexanoic acid (DHA, C22:6 (n-3)) that can be converted to the series 3 eicosanoids that may have beneficial effects at blocking inflammatory pathways. This would explain their beneficial action against cardiovascular disease, which is increasingly being seen a condition of systemic inflammation. An increase in LDL cholesterol and reduction in HDL cholesterol is a known risk factor for cardiovascular disease. However, despite attempts for many decades to prove that dietary cholesterol and saturated fat was implicated in such lipoprotein changes, this theory has now been entirely discredited by scientific evidence. Instead, data suggests that low quality diets containing highly refined carbohydrates deficient in fibre, fish oils, fruits, vegetable and micronutrients, are responsible for such detrimental lipoprotein changes.
Researchers1 have investigated the effects of fish consumption on alterations of lipoprotein fraction in 22 healthy men and women over 40 years in age. Individuals consumed an average American diet for 6 weeks (50% carbohydrate, 15% protein, 35% fat, less than 0.01% EPA or DHA) before switching to either a high fish diet or low fish diet for 24 weeks. The high fish diet comprised of 56% carbohydrate, 17% protein, 26% fat, with 0.2% and 0.5% of energy from EPA and DHA, respectively. The low fish diet was very similar to the high fish diet but contained little fish oil (<0.02% total energy). The two intervention diets resulted in a reduction in all sub fractions of LDL cholesterol, which can be explained by an increase fibre and a reduction in refined carbohydrate intake, as higher quality foods replaced lower quality alternatives.
However, those subjects consuming the high fish diet had a number of beneficial changes not seen in the low fish diet. In particular, the high fish diet produced a significant reduction in medium and small very low density lipoproteins (VLDL), indicating a reduction in de novo lipogenesis, likely caused by the reduction in refined carbohydrates. Both diets reduced HDL cholesterol concentrations, however, the high fish diet significantly reduced the HDL fraction containing both apolipoproteins (apo) AI and AII (LpAI:AII) whereas the low fish diet significantly lowered the HDL fraction containing only the apo AI (LpAI). HDL containing LpAI:AII is believed to be less efficient at exporting cellular cholesterol, compared to HDL containing just apo AI (LpAI). Fish oils therefore appear to lower the least favourable LpAI:AII while maintaining the most favourable LpAI, and this may partly explain the anti-arthrogenic effects.
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