Essential Fatty Acids – An Overview
One of the latest trends in human nutrition is the increasing importance being attached to fatty acids in the foods we eat and the supplements we take. Is this just a fad or is there some scientific backing for the claims and theories being put forward?
This paper is written as an attempt to explain the background to this complex subject, and to clear up any misunderstandings that readers and consumers may have. It is based on the latest research and findings from world experts in the field of human nutrition, and in some instances contradicts traditionally held views and opinions. In this respect it reflects the rapid advances being made in this field as a result of extensive research and re-examination of conventional theories.
This paper is not intended as an authoritative meta-analysis of available data, but rather as a discussion document for general educational purposes. The author accepts no responsibility for any way in which the information presented within this document is used by any other party.
A number of dietary factors play an essential role in permitting, maintaining and preserving human life and health. Collectively these factors are known as ‘nutrients’ and they can be roughly split into six different areas, these being water, proteins, fats, carbohydrates, vitamins and minerals.
Few people would question the essentiality of most of these nutrients as deficiencies show as definite diseases or particular health problems. For instance, a lack of water causes dehydration, a lack of protein leads to the distressing symptoms of kwashiorkor so often seen in news reports from famine-stricken third-world countries, and each vitamin has its own specific deficiency disease. The one area that might cause some surprise is the group of nutrients collectively called fats.
Fats – Good Guys or Bad Guys?
Ask a cross-section of people for the dietary key to good health and the majority will reply that we should ‘cut out fats’. This response comes as a result of the message that ‘to be healthy you need to be slim, and to be slim you need to avoid all fatty food.’ This doctrine has been drummed into us over the last few years both by the slimming foods industry and by well-intentioned dieticians and other health professionals.
Unfortunately, cutting all fats out of our diet is not going to make us healthy at all – in fact the very opposite is the case. This is because some fats are necessary to maintain human health and to allow certain bodily processes to take place. The reason for much of the confusion in this area is that not all fats are the same – and whilst some forms are known to be harmful, particularly when eaten to excess, others are now recognised as being essential to human life. To understand the differences, we need to look at the chemical structure of fats.
So What is Fat?
All dietary fats or lipids are predominantly composed of substances called triglycerides or triglycerols. These are made up of one molecule of glycerol, to which are attached three fatty acids. The following diagram illustrates the basic structure of a triglyceride, albeit in a very simplistic manner. All dietary fats share this same common format, whether they are from animal sources such as butter, suet or cod liver oil, or from vegetable sources such as olive oil, sunflower oil or coconut oil.
Diagram 1 – Simplified structure of a triglyceride or dietary fat.
So, if all dietary fats share the same basic structure, what is the difference between say butter and olive oil, or cod liver oil and coconut oil? We know that some fats are solid at room temperature and others are liquids, but what causes that difference? We are told that some kinds of fat are necessary for good health, but that others are bad for us – why?
The answers lie in the fatty acids that are attached to the glycerol molecule in the fat.
In any triglyceride compound, the only thing that is always the same is the glycerol molecule. However, the three fatty acids that combine with the glycerol molecule are different in every fat and oil that we consume. It is the different properties of these fatty acids which give the lipid its unique characteristics, and determine such physical properties as its melting point, smoke point, and so on. It is also the fatty acids that are found in the lipid that determine whether it is beneficial to our health or not.
Fatty Acids – Family Values
There are many different fatty acids, each of which has a unique molecular structure. All fatty acids consist of a chain of carbon atoms, usually even in number. The number of carbon atoms in the chain can be as few as 4 or as many as 30 or more, but the most common lengths are between 18 and 22. At one end of this chain are attached 3 hydrogen atoms (the methyl end of the molecule) and at the other end 2 oxygen atoms and 1 hydrogen atom are attached (the acid end of the molecule). In between the two ends of the chain a varying number of hydrogen atoms are attached to the intervening carbon atoms.
All naturally occurring fatty acids belong to one of three distinct families or groups. These families of fatty acids are called Saturated, Mono-unsaturated and Poly-unsaturated respectively, and the titles refer to the nature of the links between the carbon atoms that make up the fatty acid chain.
Group 1 – Saturated Fats
In a Saturated fatty acid, such as that illustrated in Diagram 2, all of the available bonds to the carbon atoms in the chain are saturated with hydrogen. This creates a very stable molecule, which is unlikely to react easily with other substances. Molecules similar to this are found in fats that are solid at room temperature and in fact the one illustrated with a chain of 10 carbon atoms has a melting point of 32C (90°F). Saturated fats with longer chains generally have higher melting points – for example palmitic acid, which has a chain length of 16 carbon atoms, has a melting point of 63C (145°F).
Diagram 2 – illustration of the molecular structure of a saturated fatty acid with a carbon chain 10 atoms long
Saturated fats are a valuable source of energy for the body. However, excessive intakes of saturated fats, particularly the longer chain ones, can lead to health problems by increasing levels of triglycerides and cholesterol in the bloodstream. This in turn can cause the formation of plaques in the arteries which are a major symptom of atherosclerosis or ‘hardening of the arteries’. The major dietary sources of these long-chain saturated fatty acids are animal fats such as those found in beef, pork, lamb and dairy foods, and people eating diets based on these often suffer more from cardiovascular disease. This is further aggravated by the fact that excess sugar intake also leads to the formation of long-chain saturated fatty acids in the body, and diets rich in animal fats often have a high sugar content as well.
Group 2 – Mono-unsaturated Fats
In the molecular structure of fatty acids we sometimes find the situation where not all of the available bonds to the carbon atoms that make up the chain are taken up by hydrogen atoms. We say that such a molecule is unsaturated and this results in a ‘double-bond’ between two of the carbon atoms in the chain. This is shown in Diagram 3.
Diagram 3 – illustration of the molecular structure of a mono-unsaturated fatty acid. The double-bond can be seen between the 7th and 8th carbon atoms from the methyl end.
This double-bond gives an unsaturated fatty acid several special properties. Structurally, the double-bond puts a ‘kink’ in the otherwise straightness of the carbon chain. This makes the triglyceride molecules more difficult to stack closely together and the result of this is that an un-saturated fat is more likely to be liquid than solid at room temperature.
A good example of a mono-unsaturated fatty acid is oleic acid, which forms the majority of triglycerides found in olive oil. This has a chain of 18 carbon atoms, with one double-bond between the 9th and 10th. At room temperature olive oil is a clear liquid, but if chilled in a fridge it becomes cloudy and starts to solidify.
The double-bond is also an area of weakness in the molecular structure of the lipid. Whereas saturated fatty acids are stable and unlikely to react chemically, the double-bond in an un-saturated fatty acid creates an opportunity for reactions to take place. Very often, the reactions that take place are a form of oxidation and may act as a trigger for other functions and actions in the body.
Group 3 – Poly-unsaturated Fats
Where fatty acids have more than one double-bond in their structure they are referred to as poly-unsaturated. As with mono-unsaturated fatty acids, the double-bonds cause ‘kinks’ to form in the structure of the molecule. The more double-bonds that occur, the more kinks will be present, and the more kinks there are, the more difficult it is for the molecules to stack closely together. It therefore follows that poly-unsaturated fatty acids (PUFA’s) are the most liquid of fats and they form the bulk of the well-known vegetable oils used in our diets today. Diagram 4 illustrates the structure of a poly-unsaturated fatty acid.
Diagram 4 – illustration of the molecular structure of a poly-unsaturated fatty acid. The double-bonds can be seen between the 3rd and 4th and the 6th and 7th carbon atoms from the methyl end.
As already explained, double-bonds within a fatty acid molecule decrease its stability and increase the likelihood of oxidative reactions. Because they have more double-bonds than mono-unsaturated fats, poly-unsaturated fatty acids are much less stable and are far more reactive, particularly to oxygen. It is this increased tendency to react with oxygen that causes many poly-unsaturated fats to quickly go rancid when exposed to the air – their rancidity is a sign of oxidation.
Oxidation can be delayed by preventing contact with oxygen and by shielding the oils from light sources. This is the reason why many poly-unsaturated oils are packed in opaque black containers and are nitrogen flushed to remove all oxygen before they are sealed. Exposure to high temperatures during extraction, storage and consumption should also be avoided as that too will increase oxidative damage.
Poly-unsaturated fatty acids are further sub-divided into a number of groups that are identified by the word ‘Omega’ followed by a ‘minus’ sign and a number. The word Omega refers to the methyl end of the molecule, and the number following indicates the position of the double-bond closest to that end of the chain. The example given in Diagram 4 is an Omega-3 fatty acid and is determined as follows; starting at the left-hand, methyl end of the molecule, count the number of carbon atoms in the chain before the first double-bond. If the first double-bond appears after the 3rd carbon atom, the fatty acid belongs to the Omega-3 group; if the first double-bond appears after the 6th carbon atom, is called an Omega-6 fatty acid, and so on. (The actual method used by chemists to determine this position is different to that described, but the end results are the same.) The word Omega is often shortened, and you may also see Omega-3 written as w-3 or n-3 – they all mean the same thing.
Functions of PUFA’s
Poly-unsaturated fatty acids have three main functions in the body. Firstly, in common with the other families of fatty acids PUFA’s are a valuable source of energy. Secondly, they play an important role in the formation and maintenance of each cell membrane, ensuring proper function and stability. Thirdly, they are necessary for the production in the body of a group of complex compounds collectively called ‘eicosanoids’. We will explore this third function in more detail a little further on, but it is this combination of functions that make PUFA’s so important to human health. First we’ll take a look at which fatty acids we really need.
So, What’s Essential?
In spite of the wide range of fatty acids in the foods that we eat, and the even wider range of actions that they have on the body, it may come as a surprise to know that only two specific PUFA’s are classified as being essential to human life. These are Linoleic acid, an Omega-6 fatty acid; and Alpha-linolenic acid, an Omega-3 fatty acid.
Provided that our diet contains enough of these two PUFA’s, through a series of reactions brought about by enzyme activity, our bodies can make all the other poly-unsaturated fatty acids that it needs to fulfil the functions mentioned above. Not surprisingly, Linoleic acid and Alpha-linolenic acid are jointly known as the ‘Essential Fatty Acids’ or EFA’s.
It is beyond the scope of this paper to go into great detail over the mechanism of these reactions and the outcomes of them, but in simple terms Linoleic acid is converted firstly into Gamma linolenic acid (GLA – as found in evening primrose and borage oil) and then into a series of four other fatty acids culminating with Docosapentaenoic acid (DPA). This is known as the Linoleic acid pathway and all of the fatty acids in this sequence belong to the Omega-6 family.
Alpha-linolenic acid converts into a further five fatty acids, of which the third and fifth in sequence are Eicosapentaenoic acid (EPA) and Docosahexaenoic acid (DHA), both of which are found in high levels in fish oils. This is known as the Alpha-linolenic acid pathway and all of the fatty acids in this sequence belong to the Omega-3 family.
Different Functions of Omega 3 & 6
Earlier in this paper we mentioned the three main functions of PUFA’s as being for energy, cell membranes and for the production of eicosanoids. It is in this last area that the two EFA’s have different actions and outcomes. To understand these differences we first have to know a little about eicosanoids.
Eicosanoids are highly active substances produced in the body and used to regulate and control levels of activity in different areas including hormones, heart and circulation, energy and inflammation. There are three different groups of eicosanoids, these being Prostaglandins, Thromboxanes and Leukotrienes, and each of these has several series or sub-groups.
If we concentrate on Prostaglandins we find that there are around 30 different ones, which are further split into three different series, numbered 1, 2 and 3. The functions of the three series of Prostaglandins are very wide ranging, but in general Series 1 & 3 are considered to be more beneficial to health than those found in Series 2.
For example, Series 1 & 3 are generally anti-inflammatory whilst Series 2 prostaglandins tend to increase inflammation in body tissue. One of the Series 1 prostaglandins helps to prevent blood platelets from becoming ‘sticky’ and clumping together to form clots, whilst one of the Series 2 prostaglandins has the opposite effect and tends to encourage clotting. For most people in the modern Western world this is an undesirable action, although there are times when its action is essential, such as following an injury.
So how does this involve Omega 3 & 6 and EFA’s? The answer is relatively simple – Prostaglandin Series 1 and 2 can generally only be made from fatty acids in the Omega-6 family as found in the Linoleic acid pathway, and Series 3 Prostaglandins can generally only be produced from fatty acids in the Omega-3 family as found in the Alpha-linolenic acid pathway. Unless these essential fatty acids are present in sufficient quantities and in the right balance and proportions, the prostaglandins and other eicosanoids necessary for normal body function cannot be produced and impaired health is inevitable.
The Fatty Acid Balance
Now that we know we need a regular intake of Omega 3 & 6 fatty acids, which foods should we be eating to supply the right fats in the right quantities and the right balance?
Historically, our diet would have naturally provided a wide range of fatty acids from a variety of foods including nuts, seeds, grains, fruits and wild fish and meat. Over the centuries, and particularly in the last 150 years, our diets have altered radically and we now base our food intake on refined grains and starches and intensively produced meat and fish. These changes have had a dramatic effect on the profile of our fatty acid intake.
It has been calculated that centuries ago our traditional diet in the West provided a ratio of between 4:1 and 6:1 in favour of Omega-6 fatty acids. Coupled with this was a very low intake of saturated fatty acids and minimal sugar intake, which as we saw earlier can also lead to the formation of saturated fats in the body when consumed in excess.
By contrast, an average Western diet today provides much higher intakes of saturated fats and refined sugars, and the balance of PUFA’s has shifted to 20:1 or more in favour of Omega-6’s. This combination means that our dietary intake of fatty acids is no longer in balance with our historical needs and may go some way to explaining the increasing incidence of health problems such as cardiovascular disease, inflammatory conditions, skin diseases and hormone related problems.
When we look at the balance of n-6 and n-3 in body tissues we find that in the brain it is 1:1, in body fat it is 5:1 and in other body tissue it is 4:1. Comparing these ratios with those found in our average diet today, it is easy to see that imbalances can and do occur.
This problem can be further aggravated by following the well-intentioned advice given by some nutrition experts to cut out animal fats and to replace them with vegetable oils. For the majority of people, this would lead them to increase their intake of oils such as sunflower, corn and soya, each of which will provide high levels of n-6 fatty acids and further alter the balance away from the ideal 4:1 ratio.
It is not easy to achieve the right balance of fatty acids in the diet given the changes in food production that have taken place over the last couple of centuries. It is now very difficult to get hold of wild meat, and few of us eat a diet based on nuts, grains, seeds and other foods that provide Omega-3 fatty acids. For most of us, the only rich sources of n-3 fatty acids in the diet are oily fish, and only then when these are wild and not farmed as is often the case with salmon these days. Even so, few of us would consider eating fish at least once a day even to ensure a constant supply of these essential nutrients.
Are there any alternative ways of achieving the right balance?
Add a Little Fat to Your Life
For many people the only realistic way they can redress the balance of fatty acids in their diet, and ensure that they get the Essential Fatty Acids that they need is to supplement their diet with an oil or oils that are rich sources of these nutrients. Traditionally, people have used fish oils such as Cod liver oil for this purpose, and there is no doubt that they are rich sources of fatty acids, Omega-3 in particular.
On the down side, Cod liver oil is also very rich in vitamin A, and when taking enough of the oil to provide meaningful amounts of fatty acids, it is possible that excessive amounts of vitamin A might be consumed. Some people also find that these same amounts of fish oils can cause ‘fishy burps’ and avoid taking it for that reason. Fish oils are also unsuitable for vegetarians, vegans and anyone else unwilling or unable eat fish.
Fortunately, there is an alternative. One of the richest sources of Omega-3 fatty acids is Linseed or Flax seed oil. Containing almost 60% Alpha-linolenic acid, and nearly 15% Linoleic acid, adding this oil to the daily diet can help to redress the imbalance between n-3 and n-6 fatty acids.
This raises questions such as how much oil should be taken, how long will it take to restore the right balance, and is it enough just to take linseed oil or should it be combined with other oils?
Restore the Balance
Where it is likely that the dietary fatty acid balance is biased too far towards Omega-6 (as is the case with most people), it makes sense to try and correct this as quickly as possible. This can be done by taking a supplement with a very high proportion of Omega-3 compared to Omega-6 – an ideal ratio would be 3:1 in favour of n-3. Such a supplement could be based mainly on Linseed oil with small amounts of other nutrient-rich oils to achieve the desired ratio. A supplement should be taken at the rate of 15-30ml a day for 1 or 2 months. At the same time, the diet should be adjusted to exclude refined and heavily processed foods, and to increase consumption of green leafy vegetables, sea vegetables and oily fish.
After this 1 or 2 month period, and assuming that the recommended dietary changes have been made, it should be possible to change the balance of the oil supplement to one which provides equal proportions of n-3 and n-6 fatty acids. As with a 3:1 ratio oil, this could be based on Linseed oil, but with greater quantities of n-6 rich oils such as Sesame oil, Pumpkin seed oil and Borage seed oil added to the blend. Again, 15-30ml a day should be taken, and this can be used indefinitely.
People unable or unwilling to make the recommended dietary changes (for example vegetarians and vegans who will not eat fish) are advised to stay on a 3:1 ratio oil as it is very likely that their diets will be providing higher than average levels of Omega-6 fatty acids.
Assuming people do follow this advice and restore the right fatty acid balance, what health benefits are they likely to enjoy? We have already seen that the right proportions and quantities of both Omega-3 and Omega-6 fatty acids are essential for the production of the full range of eicosanoids, which in turn control and regulate many of our body functions.
There are several areas where the role of Essential Fatty Acids is well documented and where the importance of Omega-3 is particularly well demonstrated. These areas include the normal development of babies and young children, heart and circulatory health, inflammatory conditions and immune function.
It has been demonstrated that several fatty acids are essential for the proper development of babies both before and after birth. Specifically, arachidonic acid and docosahexaenoic acid (DHA) are necessary for the correct formation of nerves, brain tissue and the retina in the eyes. It has been shown that infants cannot effectively convert linoleic acid and alpha-linolenic acid into the longer chain fatty acids and so these must be provided in the diet. This is fine before the baby is born as, provided the mother’s diet contains adequate levels of the essential fatty acids, they will be passed to the developing foetus through the placental link. However, after birth they will only be available from the milk or formula fed to the infant. It for this reason that breast milk, naturally rich in arachidonic acid and DHA, is by far the best food for new-born babies.
Have a Heart!
Heart disease is the leading cause of death in Western cultures and clear links have been demonstrated between the incidence of this problem and intake of fats from the diet. Whilst it has long been known that high intakes of saturated animal fats increase the risk of heart disease by raising levels of LDL (harmful) cholesterol in the blood, it has now been demonstrated that dietary PUFA’s have a lowering effect on the same cholesterol. It was originally thought that this could be because the PUFA’s were replacing saturated fats in the diet, and that just avoiding those would have this effect. However, research first published in 1989 and repeated in several trials since showed that the addition of the PUFA EPA to the diet reduced the risk of death in patients with heart disease by 29% compared with those who just cut back on saturated fats. The intake of EPA used to achieve this was as little as 2.3g a week – the equivalent of just 2g of fish oil daily. It is thought that a similar effect would be obtained from taking around 10ml of Linseed oil.
Don’t Get Irritated!
There are several causes of inflammation in body tissues, some of which are clearly of external origin. However, some diseases such as Rheumatoid arthritis, Crohn’s disease and Irritable Bowel Syndrome are internal by nature and seemingly have no obvious aetiology.
However, as already discussed, although some groups of prostaglandins and other eicosanoids have anti-inflammatory actions, others increase inflammation in the body. Series 2 prostaglandins and thromboxanes and Series 4 leukotrienes are all strongly inflammatory, and people suffering from Rheumatoid arthritis and Crohn’s disease have been found to have much higher levels of these particular eicosanoids. Supplementing the diet with EFA’s, particularly Omega-3 fatty acids, reduces production of the pro-inflammatory groups and increases production of the anti-inflammatory groups. Several trials using oils rich in EPA and DHA have shown significant improvements to symptoms of these diseases within 12 weeks – a relatively short time scale in long-term chronic diseases.
Fight the Good Fight
A healthy and active immune system is essential to protect us from invasion by external pathogens such as bacteria and viruses. We are continually under threat from these as they are in the air we breath, the food we eat and the water we drink. The immune system relies on PUFA’s to manufacture antibodies, to regulate T-cell production and to control killer-cell activity.
It has been suggested that extremely high intakes of PUFA-rich oils could actually suppress immune function and that this could be used to benefit people suffering from some autoimmune disorders. Until more is understood about this action, patients with these conditions are advised to discuss with their doctor before taking very high levels of these oils. The amounts used in normal supplementation regimes will not have this action.
And Finally -
As you can now see, Poly-unsaturated Fatty Acids, and in particular Essential Fatty Acids play a vital role in maintaining normal health and body functions. As more research is carried out into the wide-ranging actions of these nutrients, our understanding of their importance is increasing rapidly.
It is now generally accepted that few if any people get enough of the right balance of fatty acids in their diet and that supplementation with these essential nutrients is the only way to ensure that optimal health is maintained.
For more information read our fact sheet about Omega 3 Fats