Thanks to Maeve Hanan, consultant dietician and health writer at DieticallySpeaking.com, for putting this piece together. Head to her bio at the bottom of the page to find her on Instagram, Facebook, and Twitter.
What is Omega-3?
Omega-3 (also called n-3) is a type of fatty acid which fits into the polyunsaturated fatty acid (PUFA) family. It is an essential nutrient, which means that our body can’t make this itself, so it relies on sources from our diet.
There are different forms of omega 3, such as:
Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA):
Our body can use these types of omega-3 efficiently, so they have the most direct health benefits.
Sources of DHA and EPA include: oily fish like salmon, mackerel, kipper, herring, sardines and fresh tuna – but not tinned tuna; shellfish; seaweed (but eating this more than once per week may provide too much iodine, (1) especially for pregnant women); omega-3 fortified products such as: milk, yoghurt, eggs and spreads; and DHA and EPA supplements.
Alpha-linolenic acid (ALA):
This type of omega-3 can be converted to DHA and EPA in our body, but this isn’t always converted in significant amounts, especially in relation to DHA, so there are less health benefits associated with ALA.
Sources of ALA include: chia seeds, linseeds, hemp seeds (and hemp seed oil), walnuts (and walnut oil), pecans, hazelnuts, products made from soybeans like soybean oil and tofu, rapeseed oil, green leafy vegetables and ALA supplements.
How Much Omega-3 Do We Need in Our Diet?
Government health guidelines recommend that we get a total of 6.5% of daily calories from PUFA, and within this at least 0.2% of daily calories should come from omega-3 (2). In terms of practical eating advice, it is recommended that we eat at least two portions of fish per week, one of which should be oily fish (3) in order to provide enough omega-3. A portion of cooked fish is roughly 140g. But the most recent National Diet and Nutrition Survey (NDNS) (4) in the UK found that the average intake of oily fish, for those over two years old, is less than one portion per week.
Although oily fish is really good for us, eating too much can have some health risks. This is because it can contain small amounts of pollutants which can build up in our body. Therefore to avoid overdoing it, it is recommended that the general public has no more than four portions of oily fish per week. There is a lower oily fish limit of two portions per week for women of childbearing age, pregnant women and breastfeeding women, in order to reduce the risk of pollutants causing harm to a foetus or baby (although omega-3 is still an important nutrient to consume during pregnancy).
As swordfish can contain high levels of mercury, it is advised that children and pregnant women avoid this, and the general public should limit their intake to one portion per week. Tuna can also contain mercury, so pregnant women are advised to have no more than four medium tins of tuna per week, and to avoid having fresh tuna as their weekly portion of oily fish if they are also eating tinned tuna. See here for more information from the NHS about eating fish and shellfish, and here for advice about how to include fish in your diet in an environmentally sustainable way.
Omega-3 and Heart Health
One of the main reasons that it is recommended to have at least one portion of oily fish per week, is because EPA and DHA are thought to improve heart health. For example, there are health claims which have been approved by the European Food Safety Authority (EFSA) (5) that EPA and DHA contribute to: normal functioning of the heart, normal blood pressure, and normal blood triglyceride levels. There is also evidence that consumption of oily fish, (6) rather than taking omega-3 supplements, is associated with a reduced risk of heart disease; including improved cholesterol levels, improved blood pressure and potentially a reduced risk of death from heart disease.
The recent study (7) (mentioned above) was a systematic review which looked at high quality research about the role of omega-3 fatty acids in preventing heart disease; both for those with no history of heart disease (i.e. primary prevention) and for those with have heart disease, or have had a heart attack or stroke (i.e. secondary prevention). This study found moderate to high-quality evidence that increasing EPA and DHA had little or no effect on heart health or death rates. Interestingly, it also found low-quality evidence that ALA supplements might slightly reduce the risk of heart attacks, death from heart disease and arrhythmia (irregular heartbeat).
However, this evidence comes mainly from studies which used supplements rather than oily fish itself. So we can’t directly compare this to the effects of eating oily fish, as whole foods seem to affect us very differently than single nutrients or using supplements; for example, the benefits related to eating fruit and vegetables can’t be achieved by taking a multivitamin. Another important point is that most of the studies involved in this review involved people who already had heart disease, so it doesn’t tell us as much about primary prevention.
Therefore, the advice to eat two portions of fish per week, one of which should be oily fish, has not changed. But this study strengthens the current advice from the National Institute of Clinical Excellence (NICE) (8) which says that “there is no evidence that omega‑3 fatty acid compounds help to prevent [heart disease]”.
Omega-6 is another PUFA which is essential for our health, it is found in: meat, poultry, certain types of fish, eggs, sunflower oil, soya oil and corn oil. Some studies suggests that having an omega-6 to omega-3 ratio (9) of 4:1 in our diet is important for reducing inflammation and reducing the risk of conditions like heart disease whereas the modern western diet has a ratio of roughly 16:1 (omega 6:omega 3). But more studies are starting to question this. For example, a Cochrane Review (10) which was released this year found that increasing omega 6 may be beneficial for heart health. And another recent review (11) of the evidence related to omega-6 and inflammation, concluded that there is evidence that a high intake of omega-6 : “Contrastingly, there is evidence that “the interaction of omega-3 and omega-6 fatty acids and their lipid mediators in the context of inflammation is complex and still not properly understood”.
Other Health Benefits Related to Omega-3
Omega 3 plays has an important role in metabolism. There are also EFSA approved health claims (12) that DHA contributes: normal brain function and normal vision. There are further approved claims that sufficient DHA intake during pregnancy and for breastfeeding women (350 – 450mg per day) (13) promotes healthy brain and eye development for their baby.
It is thought that the anti-inflammatory effects of omega-3 fatty acids may help to reduce the risk of certain types of cancer, (14) such as colon, liver, breast and prostate cancer. However, there has been some mixed evidence about this so more human studies are needed. Also related to inflammation, there is some evidence that omega-3 may be beneficial in the treatment of rheumatoid arthritis, (15) as an add-on to other arthritis medication.
Some research has found that EPA and DHA is beneficial for improving memory in older adults (16) with mild cognitive impairment. But a Cochrane review from 2012 (17) concluded that there is not enough evidence that omega-3 intake impacts dementia, or improve cognitive function in healthy older adults.
A higher intake of fish has been associated with a lower risk of depression. (18) However, a Cochrane review from 2015 (19) found insufficient evidence about whether omega-3s are beneficial in the treatment for depression; although they also found a ‘small-to-modest, non-clinically beneficial effect’ in terms of reducing the symptoms of depression.
It is important to mention that fish provides other important nutrients as well as omega-3, which may partially explain why eating fish seems to be better for us than taking omega-3 supplements. For example, fish also provides: protein, iodine, selenium, calcium, vitamins A and vitamin D.
Advice About Omega-3 Supplements
Although supplements do not seem to be as good for us as eating oily fish, and omega-3 supplements aren’t advised for the prevention or treatment of heart disease, some people with very low intakes of omega-3 may benefit from using supplements; especially if this has been advised to you by your doctor or Dietitian. For those who do want to try an omega-3 supplement it is best to choose a supplement which: contains around 450mg of EPA and DHA per day (for adults); contains omega-3 oil rather than fish liver or cod liver oil; and is age-appropriate as there are different versions available for adults and children. It is also important to make sure omega-3 supplements don’t contain too much vitamin A, especially if you are pregnant or planning a pregnancy. You can also speak to your doctor or dietitian for personal advice about this.
Advice for Vegans
The best option for those who don’t eat fish is to include sources of ALA in their diet, like: chia seeds, linseeds, walnuts, soybeans, hemp seeds (and walnut/soybean/hemp seed oil), rapeseed oil, hazelnuts, pecans, green leafy vegetables and tofu. Vegans can also get some EPA and DHA from from omega-3 fortified foods and seaweed; bearing in mind advice not to eat seaweed too often due to the risk of consuming too much iodine.
Vegan EPA and DHA supplements made from algae are also available. These are especially useful for vegan women who are planning a pregnancy, as it is advised to have 350mg – 450mg of DHA per day during pregnancy and breastfeeding (20) to support infant brain and eye development. For more information about omega-3 supplements for vegans, you can check out this post by the Vegan RD. (21)
Take Home Message
For good health we are recommended to have two portions of fish per week, one of which should be oily fish. This is mainly related to evidence which has found that this improves heart health, but there is also good evidence that omega-3 plays an important role in eye and brain health for: a developing foetus, babies and adults. There is now strong evidence that omega-3 supplements do not seem to have the same heart health benefits as including oily fish in your diet, which may be related to the ‘whole food effect’ of oily fish. Omega-3 may have a role in reducing the risk of certain cancers, treating arthritis, improving memory in older adults and treating depression; but further research in these areas is needed.
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