The right balance: The Irish Nutrition and Dietetics Institute says that we should be taking about 30 per cent of our calories from fats. This is contradicted by the World Health Association, however, which says that fat should make up 15-30 per cent of the diet and that where obesity is prevalent, the target should be the lower end of the scale.
The right balance within fats is to get 6-10 per cent of energy from Omega 3 and six fatty acids, so on a reduced fat diet (ie where fats make up 15-20 per cent of calories) Omega 3 and 6 would make up as much as half of what we should be eating.
The effect of inadequate and imbalanced essential fatty acid consumption
Omega 3 has an impact on brain and eye development in children, and deficiencies have now been linked with numerous diseases in adults, including cardiovascular disease, rheumatoid arthritis and various cancers.
Omega 6:3 imbalances are associated with inflammatory diseases. Omega 6 competes with Omega 3 to be the substrate for cell production, but whereas Omega 3s have an anti-inflammatory action, Omega 6 is pro-inflammatory and inflammation is also in turn linked to numerous chronic diseases. Omega 6, in the words of Alan Chaytor Grubb, "can mediate degenerative diseases".
In the US, the proportion of Omega 6: Omega 3 consumed is on average at least 10:1 and has been assessed as high as 24:1. The World Health Organisation recommends around 4:1. Loren Cordain, who studies the original human diet, says a ratio of 1:1 is probably more likely to be the optimal.
Can we get them any other way?
This link gives you a breakdown of foods that contain Omega 3 and the quantities: http://www.tufts.edu/med/nutrition-infection/hiv/health_omega3.html.
The surprising conclusion is that Omega 3s are difficult to source even in green vegetables. The advice from health professionals to eat more oily fish is evidently sound but flax oil products are becoming more widely available at high quality. Walnuts are a good source but of all the nuts they will go rancid the fastest.