Omega-3s are a type of polyunsaturated fatty acid named due to their structure. In omega-3s, the first double-bond (where a hydrogen atom is missing) is 3 carbon atoms from the omega (methyl) end of the molecule. In contrast, the closely related omega-6s, the first double bond is at position 6.
Both types of fatty acid are oils at room temperature and act as essential building blocks to make cell membranes, sex hormones, and hormone-like chemicals called prostaglandins. But because of the position of their double bonds, your body handles omega-6s and omega-3s in different ways.
Omega-3s can be converted into substances (series 3 prostaglandins and series 5 leukotrienes) that help to reduce inflammation, while omega-6s can be converted into substances (series 2 prostaglandins and series 4 leukotrienes) that promote inflammation in excess. The one exception is GLA (gammalinolenic acid), an omega-6 found in evening primrose, starflower (borage) and blackcurrant seed oils, which can also reduce inflammation when intakes are sufficiently high.
Omega-3s are mainly derived from nuts (especially walnuts), flaxseed, hemp and fish oils (having originally come from the plankton on which these fish feed) plus grass-fed wild game meats such as venison and buffalo.
Omega-6s are mainly derived from vegetable oils such as sunflower, safflower and corn oils.
As your cells can’t convert omega-6s into omega-3s (or vice versa), it’s important to obtain a balanced intake.
Most of us get too few omega-3s
Our ancestors evolved on a diet where the ratio of omega-6s to omega-3s was optimally balanced at around one-to-one. The use of vegetable oils in modern processed foods mean that the ratio of omega-6s to omega-3s in a typical Western diet is now between ten-to-one and twenty-to-one.
To make things slightly more complicated, omega-3s have different effects in the body depending on their length. Those classed as short chain omega-3s (eg alpha-linolenic acid, or ALA, with 18 carbon atoms) must be converted onto the important long-chain omega-3s EPA (eicosapentaenoic acid with 20 carbons), and DHA (docosahexaenoic acid with 22 carbons) for optimal health. Unfortunately, this conversion is inefficient, with only 5% to 10% of dietary ALA converted on to DHA.
The enzymes that perform this vital conversion (eg delta-6–desaturase) are readily blocked by other diet and lifestyle factors such as:
- Excess intakes of omega-6s, sugar or alcohol
- Dietary lack of vitamins and minerals, especially vitamin B6, zinc and magnesium
- Crash dieting
- Smoking cigarettes and exposure to other toxins.
So, even if you obtain a balanced intake of omega-3s in the form of short-chain ALA, you may still have a low level of DHA and EPA.
It is estimated that at least eight out of ten people do not get enough long-chain omega-3s as so few of us eat oily fish, which are the main dietary source. National surveys show that two out of three adults and nine out of ten teenagers eat no fish at all.
Some staple foods such as margarines, bread and milk are fortified to contain omega-3 oils, although these are usually added in the form of the short-chain omega-3 ALA. Although this helps to boost omega-3 intakes for those who do not each much fish, only a small amount is converted on to the long-chain EPA and DHA which provide the proven health benefits.
Fish oils (or algae oils if you are vegetarian) remain the best source of EPA and DHA.
How much fish oil do you need?
The minimum desirable intake of long chain omega-3 fatty acids is around 450mg (0.45g) per day. Some experts suggest higher amounts of 1g EPA/DHA per day, which is equivalent to eating 2-3 medium servings of oily fish per week.
Unfortunately, the presence of marine pollutants means that the recommended intake of fish is capped. Official guidelines advise that:
- Girls and women of child-bearing age should eat no more than two portions of oily fish a week to reduce exposure to mercury, dioxins and PCBs (polychlorinated biphenyls) which could harm future pregnancies.
- Boys, men and women who are past reproductive age should eat no more than four portions of oily fish per week.
As a result, the usual recommendation is to eat two portions of fish per week, one of which is oily fish. Although two servings a week is less than ideal for optimum health, few of us actually achieve this. Average intakes are one-third of a portion of fish per week, with two-thirds of adults eating no fish at all.
Even if you eat white fish or canned tuna, you are likely to be deficient in omega-3 as these beneficial oils are only present in low quantities in white fish, and are extracted from tuna during processing to ensure a longer shelf life.
Average intakes of omega-3 are in the region of 1g EPA/DHA per week rather than the optimum 0.45g – 1g per day.
Farmed versus wild salmon
Wild salmon have consistently higher proportions of long-chain omega-3s (20-40%) compared with farmed fish (9-26%).
Although farmed salmon remains an excellent source of omega-3s, research from Stirling University suggests that the level of omega-3 in farmed salmon has halved over the last five years. This is due to changes in the way farmed salmon are fed. As a result, you now need to eat two portions of farmed salmon to obtain the same level of omega-3 as was present just a few years ago.
One exception to this is Lochmuir salmon available from Marks & Spencer who have not allowed the omega-3 levels of their salmon to drop. If you buy farmed salmon, this is the one to go for!
Why EPA and DHA are important for health
As well as promoting inflammation, there is increasing evidence that obtaining too many omega-6s and too few omega-3s may promote diabetes and obesity, increase the risk of heart attack and stroke, as well as contributing to the inflammatory diseases such as eczema, asthma and arthritis.
The long-chain omega-3s, EPA and DHA, are increasingly recognised as protecting against heart disease and stroke. They also make up around 40% of brain cell membranes and play vital roles in memory and helping you think straight.
When it comes to heart health, a new risk factor for sudden cardiac death has been suggested, known as the omega-3 index. This is measured as the percentage of EPA and DHA among the total fatty acids found in red blood cells. An omega-3 index of greater than 8% is associated with a 90% reduced risk for sudden cardiac death, as compared to an omega-3 index of less than 4% and could become a new goal for treatment with EPA and DHA.
European authorities have authorised health claims that the long-chain omega-3s are required for normal blood pressure, normal blood triglyceride levels, brain function, heart function, and vision, and are also important during pregnancy and breastfeeding to support the brain and eye development of developing babies.
What does the research show?
The best way to show the effectiveness of fish oils is to pool the results of as many randomised, placebo-controlled trials as possible and analyse them together. This will rule out any positive or negative findings that were due to chance alone. Known as a meta-analysis, this supports the benefits of taking fish oil supplements in preventing or treating many different health problems.
Fish oils lower blood pressure
Data from 8 studies involving 56,000 people show that having a good circulating level of omega-3s – especially DHA can cut the risk of developing hypertension by 23%. No significant association with dietary fish intake was found, suggesting that supplements were important.
Fish oils improve memory in older adults
Results from 28 trials involving over 6,700 people show that taking more than 1g DHA/EPA per day improved memory function in older adults with mild memory complaints.
Fish oils improve depression
DHA plays an important structural role within brain cell membranes, improving their fluidity so that messages are passed on more rapidly from one cell to another. EPA is involved in cell signalling and also improves communication between brain cells. Findings from 13 studies involving 1233 people show that omega-3 fish oils have beneficial effects against depression in people with major depressive disorder.
Fish oils protect against heart attack
Data from 15 studies involving fish-oil supplements or diets high in fish found that good intakes of fish oil significantly reduced the risk of death from any cause at any age, especially from heart attack, sudden cardiac death or stroke. Benefits were particularly pronounced for those who’d already experienced a heart attack and helped to prevent a second one from occurring.
Fish oils reduce abnormal heart rhythms
Results from 15 studies, involving 692 people, show that taking fish-oil supplements has favourable effects on heart rhythm (heart rate variability) which may be an important mechanism underlying the heart benefits of fish oil in preventing sudden heart deaths.
Fish oils improve chronic heart failure
Findings from 7 trials, involving 825 people with heart failure, show that fish oil supplements improve heart muscle strength, ability to pump blood and oxygen usage compared with placebo.
Fish oils protect against stroke
Data from 38 trials involving 794,000 people found that good intakes of omega 3 fish oils reduced the risk of thrombotic stroke. For those eating 2-4 servings of fish a week risk of stroke was reduced by 6%, compared with those eating 1 serving a week or less. For those eating 5 or more servings a week, the risk of stroke was reduced by 12% compared with those eating 1 serving a week.
Fish oils are beneficial in arthritis
Omega-3s help to reduce the level of inflammation in people with arthritis – especially those with rheumatoid arthritis. They may also reduce the associated higher risk of cardiovascular disease that occurs in people with rheumatoid arthritis, according to data from 18 trials involving 826 people.
Fish oils improve pregnancy outcomes
Results from 21 trials involving over 10,800 pregnant women show that dietary fish oil during pregnancy was associated with reduced risk of preterm delivery and improved size of the newborn.
Fish oils may help to prevent asthma in children
Findings from 11 studies, involving over 99,000 infants, children, pregnant or breast-feeding women, concluded that good intakes of omega-3 fish oils may help to prevent asthma in children.
One of the most common signs of an essential fatty acid deficiency is dry, scaly, itchy skin – an annoying problem that is often seen in older people, especially on the shins. Other signs associated with a lack of essential fatty acids can include:
- Dehydration and thirst
- Brittle hair and nails
- Hair loss
- Slower wound healing
- Hormone imbalances
- Low mood, emotional or behavioural difficulties.
Not everyone who is lacking in these oils have a severe enough deficiency to develop obvious symptoms, but the long-term health risks such as increased susceptibility to heart attack and stroke are more insidious and tend to creep up unnoticed.
Fish oil supplements
The limitations placed on eating deep-sea oily fish due to marine pollutants can be overcome by taking a daily omega-3 fish oil supplement made to a pharmaceutical standard known as GMP. These are screened to ensure low levels of pollutants, and are standardised to provide a consistent dose of purified oils.
If you eat the recommended two portions of fish every week, one of which is oily, you probably don’t need a fish oil supplement.
If you eat no fish, then it’s an excellent idea to take a supplement that provides at least 450mg EPA/DHA per day for general health. High-strength oils can provide around 600mg long-chain omega-3s (330mg DHA and 270mg EPA) per 1.2g.
If you eat one portion of white fish a week, then a standard fish oil capsule that typically provides 300mg long-chain omega-3s (180mg EPA and 120mg DHA) per 1g capsule is a cheaper option.
Omega-3 fish oils
Omega-3 fish oils are extracted from the flesh of oily fish such as salmon, tuna, herrings, sardines, pilchards and mackerel. They are a rich source of both EPA and DHA which are derived from the micro-algae on which the fish feed.
Omega-3 fish oils offered in the body-ready, triglyceride (TG) form are most easily absorbed and used (a better bioavailability) and, paradoxically, lower blood triglyceride levels due to beneficial effects on the liver.
Cod liver oil
The flesh of white fish contains very little DHA or EPA. Instead, as its name implies, cod liver oil is derived from the liver of cod. Cod liver oil is popular because it also contains high amounts of both vitamin A and vitamin D which provide additional health benefits.
Krill oil is derived from a shrimp-like, Antarctic crustacean. As well as providing EPA and DHA, it also contains two powerful antioxidants, astaxanthin and canthaxanthin, which give it an attractive red colour. These pigments are derived from the algae on which krill feed, and are the same pigments that give flamingos their attractive pink plumage. The combination of omega-3s plus antioxidants make krill a popular ‘super-supplement’ for reducing inflammation.
If you are vegetarian or allergic to fish, oil extracted from marine algae is a good source of EPA and DHA (and is the ultimate source of the omega-3s in fish). A typical capsule containing 250mg algae oil can provide 100mg of DHA.
Oil from mature linseed will provide the short-chain omega-3, ALA, of which some will be converted on to the beneficial long-chain forms.
Sustainable fish oil supplements
Sustainability is increasingly important for marine products. If this matters to you, then look for Friend Of The Sea or Marine Stewardship Council certification on your fish oil supplements.
Friend Of The Sea only certifies omega-3 fish oil and cod liver products that originate from sustainable fisheries and aquaculture. This shows that products are ethically sourced, using selective fish methods that do not over-exploit fish stocks, threaten the marine food chain, or harm the seabed or coral reefs.
The Marine Stewardship Council certifies sustainability of wild capture species such as krill, a shrimp-like, Antarctic crustacean which is a rich source of the long-chain omega-3s, EPA and DHA plus two powerful antioxidants, astaxanthin and canthaxanthin. Krill is a vital component of the marine food chain and this certification shows that a krill oil supplement does not impact on the feeding grounds of marine wildlife such as baleen whales, Antarctic Fur Seals and Adelie penguins.
Safety of fish oil supplements
The European Food Safety Authority have confirmed that long-term intakes of supplements providing up to 5g of EPA plus DHA per day (or up to 1g DHA alone per day) do not raise any safety concerns.
Because of their blood thinning effect, people with clotting disorders or who take blood-thinning medication (eg warfarin) should seek advice from their doctor before taking an omega-3 fish oil supplement. However, researchers have found that no significant increase in blood clotting time is expected at total daily intakes of EPA and DHA of 3g per day, or less.
If you are pregnant, or planning to be, only take a fish oil supplement designed for pregnancy, and which will contain more DHA than EPA (to reduce blood thinning effects, and to support fetal brain and eye development). Supplements such as cod liver oil, which contain vitamin A, are not recommended during pregnancy.
Most people would benefit from increasing their intake of long-chain omega-3s and cutting back on their intake of omega-6s to obtain a better balance of polyunsaturated fats.
Aim to eat more omega-3 rich:
- oily fish (2 to 4 portions per week) such as mackerel, herring, salmon, trout, sardines, pilchards, fresh tuna (not tinned)
- wild game meat such as venison and buffalo
- grass-fed beef
- omega-3 enriched eggs
- And consider taking an omega-3 fish oil supplement.
At the same time, cut out excess omega-6s by consuming less:
- omega-6 vegetable oils such as safflower oil, grape-seed oil, sunflower oil, corn oil, cottonseed oil or soybean oil (Replace with healthier oils such as rapeseed, olive, walnut or macadamia oils)
- margarines based on omega-6 oils such as sunflower or safflower oil
- convenience foods
- manufactured goods such as cakes, sweets and pastries.
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