If you have read the first post in this series and still came back for more I’m impressed. From the comments and messages that I have received (thank you all very very much) many of you appreciated going back to basic biochemistry. I don’t believe that science is an abstract concept, quite the opposite. Its applicability to everyday life is very underestimated by medical professionals and scientists alike. Either that or they believe that the public is really stupid and can’t possibly understand it. So instead they will just tell you what to do. No need to think. Baaaa.
So this particular discussion is going to be a little more in depth. I have really struggled to put together something which would be understandable but not simplistic. Please do not feel compelled to read it all at once if your eyes start glazing over. And yes, I had to skip over things and I’m hoping to get to those later. I have about 5000 words sitting in my drafts.
To refresh your memory this is where we got to in the last post.
Let’s zoom in on PUFA. As I have mentioned before there are 3 families of PUFA: omega-3, omega-6 and some omega-9. I will leave that last group for now as these fatty acids are made in our body and seem to be less clinically relevant.
The other two families are often represented in the media and health circles as ying and yang. I don’t quite agree with that as you will see. Not a days goes by that you don’t hear of another miracle PUFA perform: from curing heart disease and diabetes to depression, weight loss and sexual performance. How biologically plausible are these claims? In other words, step 1 of the Framework of Common Sense requires us to ask a question: is it supported by what we know about human metabolism?
We know that PUFA are not the body’s preferred fuel. Instead they are an important component of cellular membranes, they initiate and control inflammation, they also participate in brain and retina formation in babies and are necessary for the synthesis of cellular messengers called endocannabinoids. Phew.
Sounds pretty important, right? However, PUFA are also involved in two of the most critical processes in our body: oxidation and inflammation. Both are essential to life, both are dangerous when they get out of control, both deserve a separate post so for now just keep them in the back of your mind
From general lets move to specifics. While the resident nutritionist on the Today show might believe that all omega fatty acids in their respective family are the same it is far from the truth.
I’m sure that all of you have heard of essential fatty acids. “Essentiality” in biochemical terms means that our body cannot synthesise these by itself and has to receive them via food. It also implies that without these essential fatty acids our health and maybe even life are seriously impaired. Two of the fatty acids in the PUFA family have been found to be “essential”: omega-3 alpha-linolenic acid (ALA from here) and omega-6 linoleic acid (LA). In the beginning of the 20th century the studies by the Burr husband-wife team found that a lack of certain fats on a very restrictive diet makes some unfortunate rats very sick. Prior to this fats were considered important only as a source of energy and a delivery vehicle for vitamins A, D, E, K. It turned out that some fatty acids are much more than that.
Omega-3: parents, apple pies and essentiality
Let’s start with ALA. Its major function in the body is to be a parent, or the precursor, to the long chain omega-3 acids. When it is taken up from the diet it is converted to EPA and DHA, the two omega-3 siblings which cause much excitement in medical circles. EPA concentration in our body is very low as it seems to be converted immediately to its brother: DHA. However important EPA and DHA are, they are not “essential” in a biochemical sense, because we can synthesize them from ALA.
The problem is that this synthesis is not very efficient: the rate of conversion for ALA to EPA is around 8%. That is out of 1mg of ALA from flaxseed oil you will only make 0.08mg of EPA. DHA conversion rate is even poorer. It ranges from 0.5% in normal adults to 4% in young women (I’ll touch on that later).
Imagine you have decided to bake an apple pie on a Saturday afternoon. Maybe you are one of the millions of people who is still blissfully unaware that apple pie is not a health food. Maybe you will try to mitigate the damage by using margarine instead of butter. Maybe you had a rough week and you just don’t care. Back to the pie. There is no question that apples are “essential” to an apple pie. Most of us do not grow apples in our backyard or synthesise them in our bodies. You have to go and get apples from the outside source. But let’s say that the efficiency of apple:pie conversion is 8%. To get 800g of pure apple flesh after core removal, peeling, etc. you will need 10kg (Please note: demonstration purposes only. I did not actually measure apple:pie conversion so do not write saying you only needed 3 kg). To improve the efficiency of this process you can get an intermediate product like diced apples. You can even go and buy a whole apple pie, saving yourself all this headache.
In a similar way we don’t have to get our EPA/DHA from ALA (this is starting to sound like a children’s puzzle!). You can get your long chain omega-3 fatty acids directly from the diet. This way you will avoid the inefficient conversion and bypass the parent altogether. And as you know from the above, you don’t want to have to much of unnecessary oxidation-prone PUFA hanging around your body. Let’s focus on getting more bang for our nutritional buck.
And here are the long-awaited visuals.
This is something you need to know because the current nutritional recommendations push for more omega-3 in our diets. I will discuss the clinical evidence later but here we have the same problem as we had with every other advice: for the sake of “simplicity” all omega-3 are lumped together. Flaxseed oil, walnuts, canola oil – all contain high level of ALA, the parent molecule. They are also promoted as equally good sources of omega-3 as fish and other marine products, which are rich in EPA/DHA, the happy offspring. Meat, dairy and eggs, the way they are supposed to be (grassfed and pastured), never even get a mention.
The implications are particularly important for vegetarians and vegans. And also everyone who heeds the Government advice (hello, Meatless Mondays!) and drastically reduces their meat consumption. This well-meaning study supplemented lactating women with flaxseed for 4 weeks in an attempt to increases DHA in their breast milk for the baby’s brain and retina development. The results saw a substantial rise in plasma ALA and every other intermediate fatty acid BUT the one they were actually aiming for: DHA. While it is possible that in vegetarians and vegans this process is amplified out of necessity to survive these results are still pretty poor.
Omega-6 is also “essential” but which one?
The biochemically “essential” parent FA in the omega-6 family is LA, linoleic acid. Just like in the case of omega-3 its essentiality is very relative. True, you can induce omega-6 deficiency in rats by feeding them nothing but purified sucrose, casein and some vitamins. Omega-6 deficiency was also found in very sick patients who received their nutrition via intravenous solution (TPN) with no omega-6 fats added. Needless to say that awkward oversight has seen been rectified and modern TPN solutions do not pose such issues. In reality you literally cannot take a step without tripping over LA nowadays. Ever since the happy days of Ancel Keys, McGovern committee, farming subsidies and industrialisation of food everything that is processed, packaged, patented and promoted (wow this was 4 p’s) contains this omega-6 FA.
In the body LA follows a series of reactions the result of which is a long chain omega-6 AA, Arachidonic Acid (I promise this is the last acronym). AA is a central player in the cascade of reactions which promote inflammation. Just like in my apple pie story you can also get AA directly from the diet, namely meat and poultry, eggs and organ meats. Inflammation is not all bad, it’s an essential part of our response to injury or infection and the first step of the healing process. But like all good things it has to come to an end. This is where the complexity and the innate wisdom of our bodies really hits you: AA itself promotes the synthesis of compounds which resolve the inflammation.
To help AA with this task we also have DHA and EPA from the omega-3 family. Therefore it is vital that we have a good balance between the key players of omega-3 and omega-6 family. I will cover inflammation and its main mediators, eicosanoids, in a later post.
One more thing to add to our little diagram is the enzymes which actually perform the conversion of short chain PUFA to long chain PUFA. Both families, omega-3 and omega-6, use the same enzymes and therefore they are in competition for them. Too much of the members of one family will interfere with the functioning of the other family. This is where the concept of a healthy 3:6 ratio comes from. High concentration of LA suppresses the conversion of ALA to EPA and DHA. On the other hand too much EPA can cause AA deficiency.
Most of the processed pre-packaged food come with a surprise addition of LA in form of soybean oil, sunflower oil, cottonseed oil, other unspecified vegetable oil. This is the source of LA which did not even exist a 100 years ago. Because you have heard about essential fatty acids and how important they are, you also go out of your way to buy health products which contain them like nuts and nut butters, seed trail mix, nut bars etc. You know all about the important omega-3 FAs so you buy flaxseed oil, walnuts and omega-3 fortified box food. The problem is that the overwhelming load of LA, inflammatory in its own right, is effectively shutting down the already-poor conversion of omega-3. And since you are getting most of your omega-3 from plant sources in the from of ALA you need that conversion!
So where does this all leave us? “Essentiality” is a biochemical concept which can be misleading if applied to the actual food. In reality the essential (=very important) fatty acids seem to be DHA and AA, possibly EPA. Even the most important PUFA are only needed in small quantities which is reflected in the composition of breast milk and animal tissues. The conventional wisdom tells us that just because they are essential more must be better. We can argue about the actual requirements (I bet you have noticed that I haven’t offered ”the perfect ratio” or the required percentage of PUFA in the diet) however it is probably not very useful. Evolutionary clues should tell you that eating meat, some fish, eggs, pastured dairy and some plants will give you all the PUFA you need. Supplementing with artificial sources may just be akin to playing with fire.
Good sources of further basic information:
2. IUPAC (International Union of Pure and Applied Chemistry) Lexicon of lipid nutrition
3. DHA-EPA Omega 3 Institute (good for food sources)
4. SciTopics: Lipid Peroxidation
5. The medical biochemistry page: Omega-3, and -6 PUFAs
6. Julianne’s Paleo and Zone Nutrition: omega-3 and omega-6 post
And of course there are loads of posts from people much smarter than me like Peter from Hyperlipid, Stephan from WholeHealthSource, Dr Harris from Archevore and others addressing more intricate issues around PUFA.
Edit: a few typos and broken links, my bad.