From what I understand you can only get EFAs from certain kinds of fish and flaxseeds, neither of which the US diet is very high in. But we are not dying by the thousands from this dietary deficiency from what I can tell. Vitamin C is essential, w/o it you get serious diseases. Calcium is essential, protein is essential, etc. But why are essential fatty acids considered essential, it looks like our diet gets almost none but people don’t seem to have any major side effects from this.
WRT nutrients, “essential” just means that your body can’t synthesize them.
There’s also the sense of “essential” meaning (from the OED) “That is of the nature of, or resembles, an essence or extract; that is in a state of essence.” In other words, something that is extracted from a particular source can be called “essential” in this sense. I’m not sure if this is the sense meant here, though.
EFA’s are also available in whole grains, nuts and seeds, so they’re not as hard to come by as you may think. Deficiency can be marked by skin troubles (dryness, eczema, etc.), hair loss, thining or dry, brittle hair. Which lots of Americans do have. Do they all have EFA deficiency? Maybe not. But when I see a rail-thin woman on a low fat diet who’s main complaints are dry skin, eczema and thinning hair, I’ll steer her towards flaxseed and 90% of the time, it helps.
Aparently you can also get EFAs from leafy vegetables so chances are you are getting more of the stuff than you realise, even big macs have lettuce in right?
It’s not just the amount of EFAs that’s important, but the ratio of [symbol]w[/symbol][sub]3[/sub] acids to [symbol]w[/symbol][sub]6[/sub] ones. Ideally, they should be 1:1, but most people would need a lot more [symbol]w[/symbol][sub]3[/sub]s to hit that.
The trick is in a misperception in the initial sentence of the OP. You can get essential fatty acids from a wide variety of sources. However, the majority of them include high-cholesterol fats providing a lot of non-essential fatty acids as well. And unless you’re doing work that metabolizes the majority of the fats you eat, you end up depositing the non-E FAs, sometimes in very unhealthy ways. We use a lot of fatty acids; they’re the highest-energy source metabolic “fuel.” But only the few (three?) that we cannot synthesize from the others are the EFAs.
So stuff like this is saying, “We provide you your daily requirement of EFAs without subjecting you to unneeded and unhealthy fats you don’t need.” It’s easy to misread this as saying they’re the only sources of EFAs, when in fact they’re not. What they are, are the primary sources of EFAs that don’t also provide you with LDLs and other undesiderata.
If you don’t get essential fatty acids, your body won’t be able to synthesize some very necessary components, useful for neurologic development, immune system function, cardiac operation, among other things. Every cell membrane needs some essential fatty acid in it’s structure.
Here’s a nice link about EFA chemistry: http://www.benbest.com/health/essfat.html
Some of the claims may be a bit overblown, but the basic biochem seems pretty sound.
You can’t get EFAs from leafy vegetables unless they have fats in them. And the fat content of most leafy vegetables - and especially lettuce - is essentially zero, on the order of a couple of tenths of a gram per 100 gram serving.