If you take a cow and feed it on grass it gets quite a lot of omega 3 fatty acids. If you feed it on a barley based concentrate feed it doesn't get nearly so many, just loaded up on omega 6s. Because cows have a rumen they actually live on a combination of volatile fatty acids produced by bacteria, which breaking down that otherwise useless fiber in grass, plus bacterial protein. Not much of the grass itself actually gets through to the cow. Most bovine fat is self assembled from things like butyric acid or acetate, so it's fully saturated or monounsaturated, ie typical mammalian produced fat. But some essential fatty acids do get through, after all they're essential to the cow just as much as they are to you and me.
How much PUFA get through the intensely reducing environment of the rumen? This paper gives some idea of the input and transformations which occur.
Table 1 shows the amounts of linoleic and linolenic acids in grass, concentrates and sliage. Grass and silage are pretty much the same, with one part omega 6 (linoleic, 18:2) to three parts omega 3 (linolenic, 18:3). That is, grass has a rather huge excess of omega three over omega six. Before it hits the rumen.
Concentrates don't. They're not quite as bad as the "prudent" diet of the Lyon Heart study (only a cardiologist could design a diet that bad) but, at roughly eight parts omega 6 to each part omega 3, this is still cardiological profit making nirvana for the AHA.
What comes out of the rumen? The paper next looks at the fatty acid composition of intramuscular fat, the results are in Table 3. Grass only fed cattle have about 2.33 times as much omega 6 as omega 3 fatty acids in their muscles.
I firmly believe that humans evolved with an excellent ability to hunt herbivores, grass fed herbivores. On the basis that hunting provided the bulk of the lipids to a hunter-gatherer, this looks like a pretty good fatty acid ratio to aim at. Eating wild herbivores seems to be what we were good at and what should provide us with a healthy diet. Plus a bit of fishing too I guess.
The concentrates-only fed cattle were actually given some hay too, because cows tend to die if you feed them on concentrates alone, and they came out with a 4.15 parts omega 6 to each part omega 3 fats in their muscles. It's worth noting that the worst quality of grain fed Irish beef still provides an omega 6 to omega 3 ratio as good as the intake in the best ever dietary intervention trial! Still, a ratio of 2:1 looks to be even better. In both groups the PUFA made up about 5% of the fat.
The other place worth looking is Kitava , full text here, keep scrolling down to find it and try to ignore the more weird papers written by Cordain. These subsistence farmers got their lipids from fish and coconuts. There are some omega 6 fats in both fish and coconuts, but the omega 3 from the fish predominate, ie they eat less than one part omega 6 to each part omega 3. No heart disease, despite smoking. PUFA made up 10% of the lipids eaten, which were low in total at 20% of calories.
Back to cattle. What comes out in the milk? Important if you are as dairy dependent as I am. I only have data for grass fed cattle. You can see from table 3 in this paper* that PUFA run at around 5% of lipids and that there is almost a 1:1 ratio. Omega 6 come out at or just above 1% of total lipids, omega 3 at just below 1%. Hang on, that's only 2%... What are the other 3% to make up the 5% PUFA? It's mostly conjugated linoleic acid, CLA. The good stuff, the anti-cancer, anti-this pro-that CLA. Non synthetic, straight from the cow. You can see why I like dairy fats. Cows intend calves to be healthy.
That's the grass fed stuff. In general grass is cheap and concentrates are expensive, certainly here in the UK. In areas where grass will grow and wheat won't, we grow cows. Via grass. It makes quite good silage for winter use too. If you are running a dairy unit you will feed the maximum possible of grass/silage and a minimum of cattle cake. Economics dictate this. It's a hard market for dairy farmers. But even the worst case lipid scenario, using a maximum of cattle cake, would be a 1:4 ratio in cream. This is as good as the Lyon investigators got with their gloop.
Obviously neither chickens nor pigs have a rumen, so their fatty acid balance will be far more affected by the high omega six content of their diet. This is the primary reason I add 5g/day of fish oil to my diet. It goes some way to getting an essential fatty acid ratio of about one part omega 3 to, at worst, 2 parts omega 6 overall. PUFA make up about 5% of my total lipid intake, which obviously is quite high in absolute terms, due to the total amount of fat I eat.
This seems to be a very reasonable approach to PUFA for me.
Obviously all vegetable oils except olive oil are banned from the house. Banning these oils is the biggest step needed to make balancing lipids straightforward. It's possibly more important than the gloop to the Lyon heart study success. Once you crack a bottle of corn oil, sunflower oil or a pot of margarine you will never get your omega 6 intake low enough to balance things out with a few grams of fish oil. I guess that's why it's impossible to show overall benefit form one or two cod liver oil capsules a day in a "normal" diet...
Olive oil gets used in our house as a flavouring, never for bulk calories. Actually, so does a small amount of sesame oil too...
The food has to taste good as well as being nutritious!
I don't regard fish oil as a supplement. I look on it as a tool for correcting the fatty acid defect ubiquitous in UK non ruminant fat. It even makes the excellent dairy lipids better.
*Oh, I just found that the milk-lipids paper is on my hard drive as a pdf and it's not on pubmed. No idea where I got it from! It's:
Elgersma, A., S. Tamminga, and G. Ellen. 2003. Effect of grazing versus stall-feeding of cut grass on milk fatty acid composition of dairy cows. Proceedings of the Int. Occ. Symp. of the European Grassland Federation, Pleven, Bulgaria, May 2003. Grassland Science in Europe 8: 271-274.
if anyone want's to chase it!