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Note: Milk, cheddar, American, and Swiss from US Department of Agriculture Handbook No. 8; Greek myzithra and Greek feta from National Institute on Alcohol Abuse and Alcoholism analyses. Source: From Simopoulos, 1998b.

Note: Milk, cheddar, American, and Swiss from US Department of Agriculture Handbook No. 8; Greek myzithra and Greek feta from National Institute on Alcohol Abuse and Alcoholism analyses. Source: From Simopoulos, 1998b.

A balance existed between omega-6 and omega-3 for millions of years during the long evolutionary history of the genus Homo, and genetic changes occurred partly in response to these dietary influences. During evolution, omega-3 fatty acids were found in all foods consumed: meat, wild plants, eggs, fish, nuts, and berries. Recent studies by Cordain et al. (1998) on the omega-3 fatty acid content of wild animals confirm the original observations of Crawford and Sinclair et al. (Crawford, 1968; Sinclair et al., 1982). Furthermore, rapid dietary changes over short periods of time as have occurred over the past 100-150 yr is a totally new phenomenon in human evolution.

Linoleic acid and LNA and their long-chain derivatives are important components of animal and plant cell membranes. When humans ingest fish or fish oil, the EPA and DHA from the diet partially replace the omega-6 fatty acids, especially AA, in the membranes of probably all cells, but especially in the membranes of platelets, erythrocytes, neutro-phils, monocytes, and liver cells [reviewed in Simopoulos, 1991]. A diet that has a high ratio of omega-6 : omega-3 fatty acids has detrimental effects on eicosanoid metabolism and gene expression.

Because of the increased amounts of omega-6 fatty acids in the Western diet, the eicosanoid metabolic products from AA, specifically prostaglandins, thromboxanes, leukotrienes, hydroxy fatty acids, and lipoxins, are formed in larger quantities than those formed from omega-3 fatty acids, specifically EPA. The eicosanoids from AA are biologically active in very small quantities and, if they are formed in large amounts, they contribute to the formation of thrombus and atheromas, to allergic and inflammatory disorders, particularly in susceptible people, and to the proliferation of cells. Thus, a diet rich in omega-6 fatty acids shifts the physiological state to one that is prothrombotic and

Table 8

Estimated n-3 and n-6 Fatty Acid Intake in the Late Paleolithic Period (g/d)

Plants

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