The n-3 fatty acids docosahexanoic acid (DHA, C22:6 (n-3)) and eicosapentanoic acid (EPA, C20:5 (n-3)) found in fatty fish have been shown to possess a number of important health benefits, particularly the prevention of cardiovascular disease. Because of this, researchers are interested in understanding relationships between fatty fish consumption, the health of individuals, and the amount of fish consumed. For example, researchers1 used data from the European Prospective Investigation into Cancer to compare the fish and fish oil intakes obtained using 4 dietary methods, to the plasma phospholipid levels of n-3 fatty acids in 4949 men and women from the United Kingdom. The 4 dietary methods for estimating food intake were the food frequency questionnaire, the health and lifestyle questionnaire, the 7-day diary and the first day recall from the 7-day diary methods.
The data showed that the amount of fish consumed and the n-3 fatty acids levels of plasma did not differ between the 4 types of dietary analysis. When the researchers combined the data from all 4 methods there was no improvement in the estimates of fish consumption, suggesting that all 4 methods are valid for use in research. The food questionnaires and diaries showed that the population consumed moderate amounts of fish (≈2 portions per week, and about three-fourths of a portion of fatty fish per week). The highest recorded intake of fish was 4 portions per week. These figures suggest the UK consumes less fish than in Spain, France, Greece and Scandinavia, but more than Germany, the Netherlands and Italy. The figures are similar to another study conducted in the United Kingdom, and therefore support previous findings.
The plasma levels of n-3 fatty acids were significantly higher in women that men. They were also higher in fish eaters than non-fish eaters in absolute and percentage terms. However, fish oil and fatty fish consumption explained only ≈20 and 25 % of the variation in n-3 plasma phospholipids in men and women respectively. Other studies have found relatively high proportions of n-3 fatty acids in the plasma phospholipids of non fish consumers and this is likely to be due to consumption of alpha linolenic acid (ALA, C18:3 (n-3)), which can be metabolised into EPA and DHA in humans, although the conversion is not good. The sex difference in plasma levels between men and women were equivalent of the consumption of an extra half portion of fish per week. These differences in plasma levels of n-3 fatty acids may be due to hormonal differences between the sexes.
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