The essential fatty acids alpha linolenic acid (ALA, C18:3 (n-3)) and linoleic acid (LA, C18:2 (n-6)) are required in the diet because they are essential to health but cannot be synthesised in the body. These two polyunsaturated fatty acids pass down a metabolic pathway that results in the production of longer chained and more unsaturated fatty acids, which in turn form a series of short lived hormonal type compounds called eicosanoids. These eicosanoids regulate cell function, and in particular have a strong effect on the inflammatory process. The dietary LA not oxidised as a fuel is converted to the series 1 and series 2 eicosanoids. Series 1 eicosanoids are strongly anti-inflammatory, whereas the series 2 eicosanoids are strongly pro-inflammatory. The dietary ALA that is not oxidised as a fuel is converted to the series 3 eicosanoids which reduce inflammation because they block the production of the series 2 eicosanoids. Other omega 6 and omega 3 fatty acids in the diet can also feed into the pathway at various points.
Because the metabolic pathways that produce the various eicosanoids use the same enzymes, the omega 6 and omega 3 fatty acids in the diet compete with each other for the activity of the enzymes. Too much omega 6 fat and the omega 3 eicosanoid production decreases and too much omega 3 fat and the omega 6 eicosanoid production decreases. The ratio of omega 6 to omega 3 fatty acids in the diet can therefore have a profound affect on inflammation and and cell regulation in general. The ideal ratio of dietary omega 6 to omega 3 fatty acids may be around 3 to 1, although the Western diet supplies a ratio of 10 or 20 to 1. Evidence is accumulating that some of the omega 3 fatty acids also play an important role in cognition. In particular the omega 3 fatty acid docosahexaenoic acid (DHA, C22:6 (n-3)) is required for brain function as it is a necessary structural component of brain tissue, and may also regulate neuronal activity. A high omega 6 to omega 3 ratio is therefore also increasingly being seen as detrimental to cognitive ability.
The ability of the omega 6 to omega 3 fatty acid ratio of the diet to influence cognition has been tested in children. For example, in one study1, the dietary omega 6 to omega 3 fatty acid ratios of the diets of children were estimated and the children were then put through various cognitive tests. The researchers were able to predict the cognitive abilities of the children based on their dietary omega 6 to omega 3 fatty acid ratio. In addition, the quantities of the essential fatty acids also played a role. Those children with a low ratio of omega 6 to omega 3 fatty acids did better on cognitive tasks when the absolute amount of essential fatty acids was low. However, those with a high ratio of omega 6 to omega 3 fatty acids did better when the amount of omega 3 fatty acids was high. Therefore the interaction between the omega 6 and omega 3 fatty acids is more complex than a simple ratio, as cognition also appear to be influenced by the total amount of essential fatty acids in the diet, and this likely relates to the competition for enzymes in the eicosanoid pathway.
Dr Robert Barrington’s Nutritional Recommendation: Maintaining an omega 6 to omega 3 fatty acid ratio of around 3 to 1 is pivotal to health. Deviating from this ratio in either direction leads to disease and death. Because the Western diet contains too much omega 6 fat, it is a pro-inflammatory diet that causes disease. It is very likely that the Western diet, though its imbalanced essential fatty acid ratio, is detrimental to the cognition of those who consume it. Traditional diets such as the Mediterranean diet maintain an omega 6 to omega 3 ratio closer to the ideal 3 to 1 and therefore are anti-inflammatory diets. The total amount of omega 3 and omega 6 fatty acids in the diet may however, modify the optimal ratio somewhat.
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