Ω Omega-6 and omega-3 polyunsaturated fatty acids (PUFAs), are kinds of dietary fats which like vitamins and minerals are essential nutrients. This means that your body must obtain them from your diet as it is unable to synthesise them from other nutrients. If there are insufficient of these essential fats in your diet, your health will be compromised. However, there is more to it than that, as it is becoming increasingly clear that not only must you ingest enough of these nutrients for optimal health, but you must have them in the right proportions too.
Unfortunately modern diets tend to have an excess of omega 6 fats while being deficient in omega 3s. This imbalance appears to be a driver of many modern chronic diseases.
Understanding the role and sources of these PUFAs can help you take the necessary steps to improve your omega-6 to omega-3 ratio. That’s what this article is all about…
The infographic below gives a brief overview of omega 6 fats (left) and omega 3 fats (right) There is quite a lot in this little infographic, but hopefully as you read on it will become a little clearer.
Omega: One of the difficulties with this subject is the plethora of technical terms and the shorthand forms that are used in the literature. Omega-6 fats are abbreviated to n6, n-6, ω6 or Ω6 while omega-3 fats are shortened to n3, n-3, ω3 or Ω3. (ω and Ω are the lower and upper case of the Greek letter ‘omega’)
Ratios: The n6:n3 ratio can be expressed as a ratio, such as 6:1 indicating six times as much n6 as n3, or 1:2 which indicates twice as much n3 as n6. Some authors express it as a single number by dividing the n6 by the n3, so 6:1 becomes 6, while 1:2 becomes 0.5. To make it even more confusing some authors reverse the ratio and discuss the n3:n6 ratio!!
The evolutionary perspective
For a majority of our evolution (2 million-plus years) the human diet provided roughly equal amounts of n6 and n3 PUFAs, that is a ratio close to 1:1. Studies of hunter-gatherers shows that natural diets provide a n6:n3 ratio between 1:2 and 2:1. This is similar to the ratio found in the tissue of primates and other mammals.
It is only in the last 200 years that the Western diet begun to upset this balance by replacing simple, minimally-processed, traditional foods with large quantities of industrial, highly-processed foods. As a result, modern diets tend to have an excess of omega-6 PUFAs (n6) because of the widespread use of industrial seed oils — what many euphemistically call ‘vegetable oils’ — such as corn oil, sunflower oil and safflower oil, which are widespread in processed foods including tinned and baked goods, fried food, ready meals and take-away foods. This has led to a 20 fold increase in the intake of these oils in the last century [ref]
The availability of vegetable oils… in 1909 was 0.7 kg/person/year. The comparable figure in 1999 was 14.7 kg/person/year, a 20-fold increase.Linoleic Acid: A Nutritional Quandary, Ronald J. Jandacek, 2017
These same oils have also been promoted for use in use in home baking and frying and as spreads (aka margarine), replacing traditional fats such as lard, butter and dripping which have a better n6:n3 ratio as we shall see below. This graph shows how the levels of n6 PUFAs in US adult bodies has increased since this trend began in the 1950s. Currently, people in the developed world now obtain 6% of their calories from linoleic acid (n6 oils)
As well as being overly high in omega 6 oils, modern diets tend to be simultaneously deficient in omega-3 fats (n3) which are primarily found in seafood, grass-fed meat and a narrow range of seeds and nuts including linseed, walnuts and hemp seeds.
To make matters worse, because many farm animals, such as pigs and chickens are fed a diet rich in corn, seeds and cereal grains which are themselves high in omega-6, even the natural fats in animal products such as pork and eggs tend to be higher in omega-6 than is ideal. Animals that are fed less grain and more grass accumulate higher amounts of omega 3 in their tissue and milk, which is one reason that free-range and grass-fed animal products are healthier as they generally have higher levels of n3 and lower levels of n6 fats. There has been a move to include more omega-3 fats in animal feed to improve this situation, but so far this has only appeared in the shops in the form of omega-3 enriched eggs. A small change that can help is to buy organic meat and dairy where possible, as organic milk and meat have been shown to be higher in omega 3 than their non-organic counterparts. [ref]
A growing awareness of the evolutionary mismatch between the PUFA ratios we evolved with, compared to the those we are currently exposed to has led to considerable research. This research has identified links between n6:n3 imbalance and many diseases.
Diseases associated with an excess of omega 6 in the body
(a non-exhaustive list)
- Risk of obesity [Simopoulos, 2016]
- Adiposity and waist circumference [Torres-Castillo N, 2018]
- Risk of cardiovascular disease [Simopoulos, 2008]
- Risk of breast cancer [de Longeril M, 2014, Nindrea RD, 2018]
- Mood disorders [Berger, 2017] major depressive disorders [Husted, 2016]
- Cognitive decline and Alzheimers [Loef M, 2013]
- Spatial memory and cognitive function [Andruchow ND, 2017]
- Prostate cancer progression [Apte SA, 2013]
- Childhood asthma [Oddy WH, 2004]
- Age-related macular degeneration [Mance TC, 2011]
- Bone mineral density [Weiss LA, 2005]
- Pregnancy: offspring neurodevelopment [Bernard JY, 2013], mental and psychomotor development [Kim H, 2017]
To correct this imbalance it is important to reduce excessive n6 intake whilst also increasing n3 intake.
A lower ratio of omega-6/omega-3 fatty acids is needed for the prevention and management of chronic diseases.Simopoulos, 2006 Evolutionary aspects of diet, the omega-6/omega-3 ratio and genetic variation: nutritional implications for chronic diseases. (100+ citations!)
In this article we will look at (1) the role of these PUFAs in the body (2) the main dietary sources and how they are metabolised (3) practical suggestions for improving your n6:n3 ratio. Understanding these basics of PUFAs will enable you to make better food choices so you can improve the balance of these nutrients in your diet.
Biological function of the essential n6 and n3 PUFAs
The n6 and n3 PUFAs are used by the body in many processes and are converted into a range of molecules with important roles, including:
- Eicosonoids (affecting inflammation and other cellular functions)
- Endocannabinoids (which affect mood, behaviour and inflammation)
- Lipoxins, resolvins, isofurans, neurofurans, isoprostanes, hepoxilins, epoxyeicosatrienoic acids and Neuroprotectin D (which are involved in inflammatory responses, pain and cellular signalling)
Both classes of PUFA also
- Play a major role in cell membranes throughout the body (affecting cellular signalling and platelet aggregation)
- They are involved in nervous system development and nerve signalling
As you can see, the PUFAs have many important physiological roles throughout the body, so it is not surprising that dietary intake plays a significant part in health and disease.
PUFA metabolism: Short vs Long Chain
The infographic above, is split left/right to show omega 6 v omega 3 PUFAs, but it is also split vertically with the top showing the ‘short-chain’ PUFAs, which come primarily from plant sources, and at the bottom ‘long-chain’ varieties, which are found mainly in animal products.
The human body primarily utilises the long chain PUFAs. These are Arachidonic Acid (AA) — the long chain omega 6 — and DHA (Docosahexaenoic Acid) and EPA (eicosapentaenoic acid) — the long-chain omega 3s. All three of these long-chain PUFAs are essential to human life and health as they have vital functions in cells throughout the body, especially the central nervous system. The brain and retina are especially rich in AA and DHA, with these PUFAs accounting for an incredible 20% of the dry weight of these organs. [Håvard Bentsen, 2017]
The dietary sources of long chain n3 and n6 molecules are primarily oily fish, seafood and meat. [Ollis, 1999]
The chief short-chain omega 6 found in the diet is known as linoleic acid (LA), whilst short-chain omega 3 is known as alpha linolenic acid (ALA). These short chain PUFAs are found mainly in plant foods such as seeds and nuts or the oils derived from these. Unlike plants, humans do not possess the enzymes necessary to make these PUFAs inside our bodies, so are dependent on ingesting them. However, we do have enzymes capable of taking these short chain PUFAs and converting them into the all-important long chain PUFAs our body requires. These enzymes are shown down the centre of the diagram.
Interestingly, however, only a small percentage of ingested PUFAs actually end up being converted into their long-chain forms as the process is surprisingly inefficient. Strangely, a majority of the short chain LA and ALA ending up burned as cellular fuel. This inefficiency suggests that in our evolutionary past our diets contained plentiful supplies of long-chain n3 and n6 that we did not need to develop the capacity to convert short to long chain PUFAs more efficiently. It also explains why vegetarians have lower blood levels of long chain PUFAs than omnivores, despite consuming similar levels of short-chain PUFAs. [Rosell, 2005]
PUFA metabolism: enzyme competition
When the dietary intake of short chain n6 (linoleic acid) is considerably higher than the intake of short-chain n3 (alpha linoleic acid) the elongation-enzymes become biased towards formation of long chain n6 arachidonic acid, (AA) whilst simultaneously inhibiting conversion of ALA to long chain n3, especially to DHA. This competition for the elongation enzymes is partly behind the harmful health effects of a high n6:n3 ratio diet as it reduces the individual’s DHA status, and low DHA is now known to be detrimental, especially in relation to the function of the nervous system.
The role of PUFAs in Inflammation and heart disease
Both omega 6 and omega 3 PUFAs are involved in the production of molecules that mediate inflammation. The pathways involved are highly complex and the effects of dietary PUFAs not fully understood, but research is ongoing, and of good quality.
It is often stated that n6 PUFAs are pro-inflammatory, whilst n3 PUFAs are anti-inflammatory. This is certainly an over-simplification, especially in relation to short chain (plant derived) n6 PUFAs. Recent studies have shown that a high intake of such n6 PUFAs in healthy individuals does not induce inflammation [Vaughan 2015] On the other hand the claim of an anti-inflammatory role of n3 PUFAs appears more robust [Calder, 2017, Esther Tortosa-Caparrós, 2017].
Whilst n6 PUFAs do not appear to directly cause inflammation in healthy individuals the picture is less clear in the case of individuals whose health is compromised; For example, in obesity n6 PUFAs appear to play an inflammatory role or at least inhibit the anti-inflammatory effects of n3 PUFAs. In the case of obesity it has been shown that a low n6:n3 ratio (3:1) significantly protected against fatty liver disease, whereas a high n6:n3 ratio (11:1) did not. [Lazic, 2014]
Mice engineered to produce their own n3 (which mammals are normally unable to do) have a lower n6:n3 ratio than wild-type mice and are significantly protected from a range of inflammatory conditions including obesity, heart disease, endometriosis, colitis, insulin resistance and neuroinflammation [Marion-Letellier, 2015]. The resistance these high-n3 engineered mice exhibit to modern chronic diseases is reminiscent of that seen in the original Inuit of Greenland, who whilst living on their native diets had a very low level indeed of heart disease, diabetes and degenerative conditions. Their n6:n3 ratio was very favourable at 1:4, i.e. four times the intake of n3 then n6.
Long-chain PUFAs (from animal sources) appear more effective in the prevention of atherosclerosis than short-chain PUFAs (from plant foods) [Liu L, 2016] Likewise diets with a lower n6:n3 ratio produces reduced atherosclerotic lesions in animal studies [Wang S, 2009] Another study showed that a low n6:n3 ratio has been shown to inhibit the formation of foam-cells which play a key role in the formation of altherosclerotic plaques [Song Z 2018]
Despite the many uncertainties as to the exact effect of n6 seed oils, there are plenty of papers laying out robust arguments for reducing their consumption, such as the following paper, published in the BMJs Open Heart last year:
The consumption of seed oils high in the omega-6 polyunsaturated fat (PUFA) linoleic acid (LA) contributes to low-grade inflammation, oxidative stress, endothelial dysfunction and atherosclerosis.Importance of maintaining a low omega–6/omega–3 ratio for reducing inflammation, James J DiNicolantonio and James H O’Keefe, BMJ Open Heart, 2018
That said, there are many papers arguing the reverse. How can the views be so polarised? One reason for contradictory findings may simply be that almost everyone in the Western World now has such a high n6 intake that ‘natural’ (low) levels never appear in trial data. For a well-rounded discussion of the current state of knowledge about the role of linoleic acid in the diet I recommend Linoleic Acid: A Nutritional Quandary by Ronald J. Jandacek, 2017
Addressing the imbalance
From the above it appears prudent to shift one’s dietary n6:n3 balance closer to the evolutionary ratio (somewhere between 4:1 and 1:4). For most people this involves reducing their intake of n6 PUFAs whilst simultaneously increasing n3 dietary PUFAs.
Step 1: Reducing omega-6 consumption
The easiest way to improve your n6:n3 ratio is to avoid fats and oils that are high in omega-6 PUFAs. The chart below shows the fraction of saturated fat, mono-unsaturated fat, alpha linolenic acid (omega-3) and linoleic acid (omega-6 ) in various common dietary fats and oils:
The orange bars indicate the fraction of omega-6 in the fats and oils. To help improve your n6:n3 balance it is better to avoid fats and oils from the lower half of the table (sunflower, safflower, peanut, soybean and corn oils) as these are very high in n6 PUFAs. Furthermore, because these undesirable oils are used in so many processed foods it is important to check for them in ingredients lists.
Unfortunately, these industrial seed oils are found in many foods, including canned fish in oil, jars of olives, ante-pasta, sauces, crisps, biscuits and cakes and commercially fried foods such as fish and chips and, of course, donuts.
Step 2: Increase omega-3 consumption
The best way to increase your long-chain omega-3 PUFAs intake is to eat more oily fish (salmon, mackerel, herring, crab, tuna) To maximise your intake of seafood while minimising your exposure to toxins such as mercury see our guide:
If you are not a fish lover, the second best way to achieve an increase in n3 PUFAs is to eat meat. Although levels of omega-3 PUFAs in meat are considerably lower than in oily fish, an Australian study found that meat can make a significant contribution to n3 intake if it is eaten frequently [Ollis, 1999]. Unfortunately, many farm animals today are fed corn and grains which means they have high n6:n3 ratio in their meat.
Grass-fed, Organic and Free-range Animal Produce
The balance is much better if you stick to grass fed meat as it has higher levels of n3 PUFAs and consequently a better PUFA ratio. If you can’t get exclusively grass-fed produce, then just choose organic meat and eggs as these have been shown to be higher in n3 than their conventional counterparts (Średnicka-Tober, 2016) and organic livestock are out on pasture for the majority of the year. Supporting your local free-range or organic meat producer is an excellent way to improve your health, the ethical farmers’ health, the health and contentment of the farm animals and, of course, the health of the soil in the fields in which the animals live all add to the virtue of this choice. And any chef worth their salt will tell you that meat from organically raised livestock, is superior.
Plant based n3
Short chain ALA can be increased in the diet through the use of linseed (flax). Linseed oil is not suitable for cooking, however, so linseed is best eaten as a seed. Ground linseed can be sprinkled on salads or used as a basis for a healthy muesli substitute (see our Health Hack #3: muesli that’s worth eating). ALA still needs to be elongated, though, and as we have seen, this process is not very efficient, so this vegan form of n3 essential fatty acid may not result in sufficient EPA or DHA for full neurological health on its own.
Oils and Fats
For cooking, butter has a perfect n6:n3 ratio of 1:1, although the total quantity of both is low. Rapeseed oil has significant amounts of ALA, but should be reserved for cold use as the ALA is prone to damage when heated to frying temperatures. Salad dressings and mayonnaise are two ways to use this oil raw.
1. Avoid vegetable oils high in omega-6
2. Eat more omega-3 rich foods, including seafoods and grass-fed meat and dairy
3. If required supplement with cod-liver oil or fish-oil capsules