Omega-3: The Good, The Bad, and The Fishy
Fish oil is one of the UK’s most popular supplements, and one of the least understood. You might pick it up because you’ve heard omega-3 is good for the heart, or a GP mentioned it in passing. The trouble is that not all supplements contain what you’d hope, and the label doesn’t always make it clear. This guide covers what to look for before you spend your money.
The different forms of omega-3 supplement
Omega-3 supplements come in four molecular forms:
- Free fatty acids
- Triglycerides
- Phospholipids
- Ethyl esters
Free fatty acids absorb best – they’re the form found in oily fish. Triglycerides and phospholipids come next. Ethyl esters, common in cheaper supplements, are the least well absorbed of the four.
How to choose an omega-3 supplement
Form is just the starting point. Five things shape whether a supplement is worth buying: source, type and dose, purity, freshness, and packaging.
1. Where it comes from
If you eat fish and have no allergies, fish oil is the straightforward choice. If you’re vegan, vegetarian, or react to fish, algal oil is the main alternative. Here’s how the main sources compare:
Fish oil is the most widely available source of EPA and DHA.
- Primary source of both EPA and DHA supplements worldwide
- Available in multiple forms, extracted from different fish species
- Should undergo refining to remove impurities and heavy metals, including mercury
- Refining often converts EPA and DHA from natural triglyceride form to ethyl ester
- Some manufacturers convert ethyl ester back to triglyceride form – better absorbed, though more expensive
Cod liver oil is often confused with fish oil, but it’s a different product.
- Contains EPA and DHA, plus vitamins A and D
- Lower in omega-3 than most fish oil capsules
- Often requires 4-6 capsules to reach a meaningful daily omega-3 intake
Krill oil has attracted attention as a premium alternative to fish oil.
- Contains EPA and DHA in triglyceride and phospholipid form, which absorb well
- Some varieties contain antioxidants
- Lower total EPA and DHA than fish oil, so you need more of it per dose
Algal oil is the plant-based route to EPA and DHA.
- Primary DHA source for vegans and vegetarians
- Provides some EPA, though levels vary by product
- No heavy metal contamination risk – produced under controlled conditions
Worth knowing: Algae are the original source of omega-3s in the marine food supply. Both farmed and wild fish get their omega-3 by eating algae.
Plant-based sources such as flaxseeds, chia seeds, and walnuts contain a different form of omega-3.
- Contain only ALA, not EPA or DHA
- The body can convert ALA to EPA and DHA, but the rate is poor
2. Type and amount
Are all omega-3 supplements the same? No. A product can advertise ‘omega-3’ on the front and contain almost no EPA or DHA – the compounds that most of the research is about. Read the label carefully: does it list EPA and DHA as distinct figures, or just total omega-3? There’s a big difference. Check the amount per serving, not per capsule, and compare products on that basis.
3. Purity and freshness
Can you trust the manufacturer’s own claims about purity? Not without independent verification. Fish oil and krill oil can carry mercury and other heavy metals, and refining doesn’t always clear everything out. I’d look for products tested by an independent lab rather than just relying on the brand’s assurances.
Freshness is a separate concern. Fish oil goes rancid, and rancid oil is unpleasant and less useful. Check the manufacturing date, and favour products fortified with vitamin E, which slows oxidation.
The TOTOX value is a freshness score for fish oil. Lower is better. The oil oxidises on contact with heat, light, or oxygen, and TOTOX measures how far that process has gone.
The Anisidine value reflects the oil’s age and storage history. Again, lower is better – it indicates the oil hasn’t degraded in the supply chain.
Look for supplements that publish their TOTOX and Anisidine values on the label or website. Brands confident about their freshness numbers tend to publish them.
4. Supplement form and packaging
Most omega-3 supplements come as soft gel capsules or liquid. Capsules are the more practical option for most people.
The most common complaint I hear about fish oil is the fishy burp. Enteric-coated capsules help with this – they pass through the stomach intact and release further down the gut, so the aftertaste is much less of an issue.
Triple-strength capsules pack more EPA and DHA per dose, so you take fewer each day. They’re bigger than standard 1000mg capsules, and some people find them hard to swallow. Worth trying one before committing to a large pack.
Liquid omega-3 works for people who can’t manage capsules. Bear in mind it oxidises faster once open – it needs to go in the fridge.
For either format, a few basics apply:
- Check the manufacturing date. Fresher is better.
- Minimal fillers and additives. Fewer ingredients is a good sign.
- Some brands publish third-party testing results. Worth finding one that does if you’re spending serious money on a supplement.
The supplement that works is the one you take. A cheaper capsule you stick with beats an expensive liquid sitting in the fridge going off.
Wrapping up
Choosing an omega-3 supplement takes more thought than picking the cheapest bottle off the shelf. Source, form, dose, freshness – each one matters, and a product that looks fine on the front of the pack can tell a different story on the back.
Before buying, check:
- Source: fish oil, cod liver oil, krill oil, or algal oil – each has different EPA and DHA levels and absorption profiles
- EPA and DHA listed as distinct figures, not just ‘total omega-3’
- Purity – whether the product has been tested by an independent lab
- Format – and whether you’ll take it every day
A few practical notes before you buy:
- Check your diet first: Two portions of oily fish a week – NHS guidance – covers most adults’ EPA and DHA needs without any supplement.
- Talk to your GP or pharmacist: Worth a conversation if you’re on regular medication, including blood thinners.
- Compare products: Use the criteria in this guide – source, EPA and DHA amounts, purity, and freshness indicators.
- Start with the standard dose: No need to go straight for high-dose supplements.
FAQs
What are omega-3 fatty acids?
Omega-3 fatty acids are a type of fat your body can’t produce on its own, so you have to get them from food or supplements. There are three main forms: ALA, found in plant sources, and EPA and DHA, found in oily fish and algae. EPA and DHA are the ones most research focuses on.
Why are omega-3 fatty acids important?
The research is strongest for heart health and reducing inflammation. There’s reasonable evidence too for effects on blood pressure, triglyceride levels, and brain function. Omega-3s during pregnancy also appear to matter for foetal brain development.
What are the best food sources of omega-3?
Oily fish – salmon, mackerel, sardines, herring – are the best source of EPA and DHA. For vegans and vegetarians, flaxseeds, chia seeds, walnuts, and hemp seeds provide ALA. The body can convert ALA to EPA and DHA, but the rate is poor, which is why algal supplements are worth considering if you don’t eat fish.
How much omega-3 do I need?
Guidance varies, but most recommendations point to 250-500mg of combined EPA and DHA per day for healthy adults. For ALA, reference intakes are around 1.6g daily for men and 1.1g for women. Eating oily fish once or twice a week contributes a good proportion of this, though the exact amount depends on which fish and how it’s cooked.
Can omega-3 help with mental health?
The evidence is promising but mixed. EPA in particular has shown benefit in some trials looking at depression. There’s also a body of research around cognitive decline with age. Omega-3 is not a treatment for mental health conditions – anyone dealing with depression or anxiety should speak to their GP rather than relying on supplements.
Are supplements as effective as getting omega-3 from food?
Food first. Oily fish comes with other nutrients and fits into the broader context of a varied diet. If you don’t eat fish regularly – due to allergy, preference, or habit – a well-chosen supplement is a reasonable option. Make sure it contains significant amounts of EPA and DHA, not just total omega-3.
What should I look for when buying an omega-3 supplement?
Check the source, the actual EPA and DHA content listed as distinct figures, and whether the product has been tested by an independent lab. Freshness matters too – look at the TOTOX value if available, and check the manufacturing date.
Are there side effects to omega-3 supplements?
At normal doses, most side effects are digestive – fishy breath, heartburn, or loose stools. At doses of 3g/day or above these become more likely, and there can be effects on bleeding. If you’re on blood thinners or other regular medication, have a word with your GP before starting.
