Omega-3 Fatty Acids: What Are They Good For?

The Omega-3 Trio: Meet ALA, EPA, and DHA

Most people know they should eat more oily fish. Fewer can say why. The answer comes down to three fatty acids your body cannot make on its own: ALA, EPA, and DHA.

All three are omega-3s, dietary fats your body cannot produce, which means you have to get them from food or supplements. Each type works differently, and they come from different places.

ALA (alpha-linolenic acid) comes from plant foods: flaxseeds, chia seeds, walnuts. The body converts it into EPA and DHA, but the process is inefficient. Under 10% of ALA makes it through to EPA, and less still reaches DHA. Plant sources count, but they’re not a substitute for the marine forms.

EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) come from marine sources: oily fish and algae. These two have the strongest evidence behind them, and getting them from food or a supplement skips the conversion problem.

The Heart Benefits of Omega-3 Fatty Acids

The cardiovascular case for omega-3s is well-established, even if the full picture has grown more nuanced in recent years. EPA and DHA reduce blood triglycerides, a type of fat that, at elevated levels, raises cardiovascular disease risk. The evidence here is among the more consistent in nutrition science, and it translates into practice: triglyceride reduction through diet and lifestyle is part of how NHS cardiovascular risk management actually works.

Does eating oily fish twice a week move the needle? For cardiovascular risk, yes. The triglyceride evidence is solid, and that alone is worth taking seriously. There’s also data on modest blood pressure reductions in people with hypertension, and some research linking higher omega-3 intake to lower rates of abnormal heart rhythms. None of this is dramatic in isolation. Two portions a week is about as low-risk an intervention as you can make. Worth it.

Other Health Benefits of Omega-3 Fatty Acids

DHA is a structural component of the brain and retina. This is why oily fish features in NHS dietary guidance for pregnant women, where adequate DHA in pregnancy and early childhood supports brain and eye development. In adults, the cognitive picture is less clear, but some research links low omega-3 status to faster cognitive decline. Two or three portions a week isn’t going to hurt.

Omega-3s also reduce production of inflammatory molecules, which may explain consistent findings on joint pain and stiffness in rheumatoid arthritis. Mental health is an area of active research. Some trials show benefits for depression, with EPA-dominant supplements showing the clearest signal. The intersection of diet and mood is something I follow closely. The evidence isn’t strong enough yet to recommend omega-3s as a treatment, but it’s pointing somewhere.

For a closer look at what supplement research shows, see our Omega-3 Supplements guide. And before starting any supplement, have a conversation with your GP, especially if you’re on anticoagulants. Fish oil affects clotting at higher doses.

Sources of Omega-3 Fatty Acids: From Diet to Supplements

Getting enough omega-3s from food is achievable for most people. The main options, in order of reliability:

Fish: The Premier Source of Omega-3s

Fatty fish are the richest dietary source of EPA and DHA. SMASH is a useful shorthand: Salmon, Mackerel, Anchovies, Sardines, Herring. The NHS recommends at least two portions of fish per week, with at least one oily. Alongside the omega-3s, you get protein, vitamin D, and B12 in the same meal.

• Salmon
• Mackerel
• Anchovies
• Sardines
• Herring

Trout is worth adding to this list: decent omega-3 content, available in most supermarkets. Cod, despite being the UK’s most eaten fish, contributes little.

Mercury contamination is a real concern with some fish, but the oily species above are low risk. Smaller fish like sardines and anchovies accumulate less mercury than large predatory species. Tinned sardines or mackerel from any supermarket are as nutritious as fresh, and a fraction of the price. I tell patients this all the time. No need to overthink it.

Plant-Based Omega-3 Sources

For those who don’t eat fish, ALA from plant foods is the main route. The conversion to EPA and DHA is limited, so to get meaningful levels you’d either need large amounts of plant sources or an algae-derived EPA/DHA supplement.

Good ALA sources include flaxseeds and flaxseed oil, chia seeds, walnuts, and hemp seeds. Algae oil is the only plant-based source that provides EPA and DHA without the conversion step, making it the better option for vegans.

• Flaxseeds and flaxseed oil
• Chia seeds
• Walnuts
• Hemp seeds
• Algae oil (direct EPA and DHA)

ALA plant sources still offer anti-inflammatory and cardiovascular benefit. They’re best seen as a complement to a varied diet, not a replacement for fish or algae-derived EPA and DHA.

Omega-3 Fortified Foods

Some products are fortified with omega-3s: certain eggs (from hens fed omega-3-rich feed), some milks and yogurts, and a handful of bread and cereal products. These can contribute to overall intake, though the amounts tend to be modest.

Check the label for which type is added. Many fortified products contain ALA rather than EPA or DHA, so the benefit differs from eating oily fish.

Omega-3 Supplements

Fish oil capsules are the most common option, and for people who don’t eat oily fish, they’re a reasonable choice. Cod liver oil is a traditional alternative but contains high levels of vitamin A, making it unsuitable in pregnancy. Algae oil provides EPA and DHA without any fish and is the cleaner choice for vegetarians or vegans.

Three things worth checking when buying a supplement:

• EPA and DHA content, not just total omega-3 (ALA counts differently)
• Quality certification, such as IFOS third-party testing
• Sustainable sourcing. Look for Marine Stewardship Council certification.

Supplements fill gaps in the diet. Talk to your GP before starting, and mention any medication you’re taking.

Where to Start

If you’re not eating oily fish twice a week, that’s the most useful change to make. Tinned sardines, mackerel fillets, a piece of salmon. Cheap, convenient, and among the most nutrient-dense foods on any supermarket shelf. Two portions a week covers most people’s needs from food alone.

• Aim for two portions of oily fish a week, sardines, mackerel, salmon, or herring all count (tinned included)
• Don’t eat fish? An algae-derived EPA/DHA supplement is the most effective plant-based alternative
• On medication? Check with your GP before starting fish oil, and mention warfarin or antiplatelet drugs

Omega-3s aren’t a magic fix. But the diet-health evidence here is robust, and the intervention is low effort. Worth building in.

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