Basic biochem stuff out of the way first:
Omega-3 fatty acids are long-chain polyunsaturated fatty acids between 18???22 carbons in length. They are unsaturated because some of these carbon atom are not 'fully loaded' with hydrogen atoms, so instead they form double links with the carbon atom next to them. They are called omega 3 fatty acids because the first double bond begins with the third carbon atom (when counting from the methyl end of the fatty acid molecule).
There are a few very important omega-3 fatty acids:
- those from fish - like docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA)
- those from plants (like flax and walnuts) - mainly alpha-linolenic acid (ALA).
Only ALA is considered an 'essential' omega-3 fatty acid. This is because your body can make DHA, EPA (and other Fatty acids) from ALA. But... only to a limited degree, and only when there are sufficient conditions in the body for this to occur....
Omega-6 fatty acids are also unsaturated long-chain fatty acids where the first double bond is at the 6th carbon atom.
There are lots more sources of omega-6 fatty acids, with the ones found most in our diets from things like:
- linoleic acid (LA), found in sunflowers, soybean oils and sesame seeds
- Gamma-linolenic Acid (GLA), which is found in things like primrose oil
- And Arachidonic Acid (AA) which is the one that is found in animal sources like meat, milk, eggs etc....
Once again, only one of these is essential - that is linoleic acid - as the others can be formed in the body.
Now - The problems occur because certain things have a competative influence on the metabolism of ALA to form the fatty acids like EPA and DHA. In particular - trans fats, saturated fats and (and this is why ratios are important) LA can all interfere with this process...
This is because the same set of enzymes (desaturase and elongase enzymes) act to metabolise these things - so, if the enzymes are busy with all the omega-6s or saturated fats (which are usually converted into AA) there will not be enough for the omega-3s. So, if your diet is too high in LA, and you are not getting ENOUGH EPA or DHA, then you end up being deficient in these omega-3s.
BUT - if you have too much omega 3 (as in, lots and lots of flax) - then it limits the ability of the body to metabolise the LA - so you get a build up of this in your body.
They also compete at cellular membrane levels for lipid-membrane composition/adipose composition levels, liver fat levels and lots of other things...
Anyway...
The omega-3's EPA and DHA are extremely important for normal health in the body. They are essential in brain development and function, they help in joint lubrication and reduce the risk of arthritis, can decrease cardiovascular problems like high blood pressure and heart disease, are essential for your skin and hair, are essential in maintaining healthy kidney function and helps protect your intestines and have also been links with decreasing cancer rates.
The list goes on and on... So - if they become deficient you are asking for trouble!
Omega-6s on the other hand (esp AA) can CAUSE inflammation in the body - this is because Arachadonic Acid is an important pre-curser for imflammation. See, AA helps form what is known as the Series 2 Prostaglandins - which are 'inflammatory mediators' released from tissues when they are damaged to help initiate the imflammatory cascade. So it can do all sorts of nasty things - like increase your chances of blood clots, increase the signs of inflammatory disease like arthritis etc etc. (just on a side note - this is what anti-inflammatory drugs (known as NSAID's - like Asprin) act to prevent being formed...).
But - you do need some omega-6 in the diet!! So don't think they are all bad.... they are actually needed to for the conversion of ALA to DHA and EPA (specifically, LA is needed in small amounts) and they have been linked with decreasing cholesterol. They are also important in ensuring our bodies CAN react to injury through inflammation!! They are needed to stimulate cell repair and are important in wound healing etc.
So you have to have a good ratio of both! - that means not too much omega 6's AND not too much omega 3's.
Anyway - Way back in evolution, our diets had ratios of around 1:1 (omega 6mega 3), because we had a higher intake of fish etc, and so this competition was not a problem... but now, the ratio is more like 20:1 (omega 6: omega 3) AND, on top of this, most of that omega 3 we do get is from ALA - NOT DHA and EPA....
