Chronic low grade inflammation is now thought to be involved in the aetiology of a number of diseases, most notably metabolic syndrome, obesity and cardiovascular disease. The association of inflammation with all three of these conditions is not surprising as they likely have a common origin, that being insulin resistance and non-alcoholic fatty liver. Increasingly the cause of systemic chronic inflammation is considered to be of dietary origin, with regular consumption of the Western diet being particularly implicated. The Western diet can cause inflammation because it contains foods that are pro-inflammatory, and because it also is lacking in whole plant foods that have anti-inflammatory effects. However, increasingly the omega-3 to omega-6 fatty acid content of the diet is being considered as pivotal in the development of inflammation. Both omega-6 and omega-3 fatty acids can be anti-inflammatory.
Omega-6 and omega-3 fatty acids are associated with an anti-inflammatory effects because both alpha linolenic acid (ALA, C18:3 (n-3)) and linoleic acid (LA, C18:2 (n-6)) are precursors to anti-inflammatory eicosanoids. Increasing the intake of omega-3 fatty acids can reduce inflammation because the omega-3 fatty acids are converted to the series 3 eicosanoids that inhibit the formation of pro-inflammatory eicosanoids formed from arachidonic acid (AA, C20:4 (n-6)). In addition, LA is a precursor to dihomo-gamma linolenic acid which form the potent anti-inflammatory series 1 eicosanoids. The ratio of omega-6 to omega-3 fatty acids is also an important determinant of inflammation and an imbalance in the ratio can be a cause of disease. The exact ratio of omega-6 to omega-3 fatty acids that is required for optimal health is not known, but studies suggest that a ratio of 3 to 1 is likely close to optimal. However, the Western diet may supply a ratio of between 10 and 20 to 1.
Researchers have investigated the association between intakes of omega-6 and omega-3 fatty acids with markers of systemic inflammation such as C-reactive protein. For example, in one study1, researchers used study data to assess the levels of C-reactive protein in a group of middle-aged men and women. Dietary records were then used to assess their intakes of omega -6 and omega-3 fatty acids. The results of the study showed that there was an inverse association between the intakes of total omega-3 fatty acids as well for individual omega-3 fatty acids with C-reactive protein. In addition there was an inverse association between levels of C-reactive protein and intakes of omega-6 fatty acids. Both omega-3 and omega-6 fatty acid intakes are therefore associated with lower levels of systemic inflammation. In this study these associations were only present in those with the lowest intake of vitamin E, suggesting that vitamin E may be able to lower systemic inflammation independently of fatty acid intake.
Dr Robert Barrington’s Nutritional Recommendation: Both linoleic acid and alpha-linolenic acid are essential fatty acids and therefore required for health. These fatty acids form eicosanoids, substances that regulate tissue inflammation. It is no surprise therefore that higher intakes of both compounds are beneficial at reducing inflammation. However, the important concept to understand with regard these fatty acids is that it is not the absolute amount ingested that is the main determinant of inflammation, but the ratio of one to the other. This is one consideration the study authors above did not evaluate, and was a weakness in the design of the research. The ratio of omega-6 to omega-3 fatty acids in the diet should be around 3 to 1. Vitamin E is an anti-inflammatory compound and so it is no surprise that it can modify inflammation and reduce levels of C-reactive protein at higher intakes.