The problem with fish oil

Not a fan of oily fish? Think a supplement might be wise? Here’s what we need to know first.

There are different types of omega-3

The main health benefits of omega-3 are believed to come from two long-chain fats called EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) for short.

Fish, fish oil, krill oil (krill are tiny crustaceans), and marine algae are the main sources of EPA and DHA. Fish and krill contain omega-3 because they feed on the algae.

Walnuts and seeds such as flax (linseed), chia, hemp and pumpkin seed also contain omega-3. But this version is a short-chain fat called ALA (alpha-linolenic acid). To a small extent, our bodies can convert ALA to EPA and DHA, but most of us can’t make that conversion well.

While ALA appears to be generally healthy and anti-inflammatory, it doesn’t have the benefits linked with EPA and DHA.

These include supporting healthy blood pressure, cholesterol, and triglycerides, as well as brain and general cell function.

As for supplements, according to the research, they may also be useful for managing or avoiding diabetes, non-alcoholic fatty liver disease, depression, osteoarthritis, and rheumatoid arthritis.

But getting conclusive results is hard for the same reason that it’s hard with so many other supplements: different research teams use different forms of omega-3 and different doses, they study different types of people, those people might or might not be eating a diet that already contains plenty of EPA and DHA, and so on.

Fish vs supplements

The Heart Foundation website promotes fish (and oily seeds) in a heart healthy diet but stops short of recommending supplements. Which is fair enough because there are advantages to eating fish.

Sardines, for example, contain calcium, potassium, selenium, magnesium, zinc, iron, and vitamin D in addition to protein and EPA/DHA — a combination that seems to be good for cardiovascular health.

The only drawback is we might really have to like sardines. One study showed benefits when people ate 100g (about a can) five days a week for six months.

All fish and shellfish contain some omega-3, but the oilier ones are the best sources. There’s not a lot in low-fat fish, including most white fleshed fish.

To illustrate this, an Australian study from 2008 found that to get a gram of omega-3 we’d need to eat about 40-45g of swordfish or Atlantic salmon, about 75g of gemfish, but about 450g of a low-fat fish such as ling. For barramundi, and coral trout it was around 360g. So there’s a big difference.

The most popular oily fish in Australia is probably Atlantic salmon.

Whereas wild salmon get their omega-3 from algae, farmed salmon (the main type in fish shops or supermarkets) get it from their feed. Typically, this has come from fish meal (ground up fish) but wild fish have been used for this and efforts are being made to stop doing that. (Of course, with fish farming in the news this month, this might be the least of the environmental concerns about it.)

It’s possible to buy frozen wild caught salmon but it’s pricey because it’s been flown from places such as Norway or Canada.

When it comes to tinned fish, tuna seems to be the one we’re more likely to buy. It doesn’t have as much omega-3 as sardines, salmon, or mackeral though, and some brands add vegetable oil, so check what you’re getting.

Away from the fish world, so-called grass-fed beef is also touted as a source of omega-3. If cattle eat grass for their whole life, there’ll be more omega-3 in their meat than there otherwise would be, but most are fattened on grain and there’s precious little omega-3 in the meat after that.

By now you might be concluding that getting enough omega-3 from fish mightn’t be as easy as it sounds.

How much is enough?

The heart foundation recommends 250-500g of marine-sourced omega-3 (EPA and DHA) per day. To get that, we’re told, we’d need 2-3 serves (a serve being the size of a deck of cards or your palm, or around 110g) of fish per week. But as we’ve seen, not all serves of fish yield the same amount of omega-3.

The alternative is to take a supplement.

Can we take too much if we do a bit of both — eat some fish and take a supplement too? Apparently not, unless we need to be careful with blood thinning.

But just to complicate things, if our diet contains extra omega-6 fats (such as seed oils), that can block our absorption of omega-3. So best to minimise processed food and pass on the use of seed oils for cooking.

Also worth noting is that a study by the University of Wollongong’s School of Medicine using national nutrition data collected in 2011-2012 found that only about 20% of us get enough EPA and DHA.

What to know about fish oil supplements

Like seed oils, omega-3 is highly unsaturated, which means it’s fragile and oxidises quickly. It’ll degrade if it’s exposed to heat, water, humidity or oxygen, and that can lead to rancidity.

For this reason it needs protection. It has to stay cold and dry, i.e. be kept refrigerated. Being encased in a gelatin capsule also helps.

Here’s the problem with fish oil: most isn’t refrigerated. It’s likely to be in good condition at the factory but not refrigerated through the distribution phase, and air conditioning isn’t sufficient to stop it from spoiling.

One retailer told me that Melrose is the only brand that comes to them refrigerated. That brand is also kept refrigerated in shops. (Downside might be that it’s a liquid, not capsules, and not everyone fancies liquid fish oil, even when it’s lemon and lime flavoured. Maybe especially when it’s lemon and lime flavoured.)

The bottom line is it’s not wise to buy fish oil off the shelf. A Sydney study published in 2018 tested 26 supplements and found almost 40% were oxidised.

There are alternatives though. Krill oil, although it contains less EPA and DHA, is still a good source, and doesn’t seem to need the same care with refrigeration. That’s also true of marine algae supplements.

But scrutinise the labels and do your homework on any of them.

Bear in mind too that all of these will have blood thinning properties, so if you’re taking blood thinning medication, talk with your doctor about it.

It’s usually recommended that supplements contain more EPA than DHA, in a ratio of 2:1 or 3:2.

Lastly, there’s also cod liver oil, which is different from fish oil. As well as EPA and DHA, it contains vitamin D and vitamin A. Cod liver oil tends to be used more as an immune supplement than for cardiovascular health, for example.

In summary, aim to eat fish or seafood regularly if you can, knowing that not all fish are equal when it comes to omega-3. And if you can’t do that, look for a suitable supplement. But don’t dive in without some basic knowledge.

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