There’s a reason so many of our grandmothers lined children up for a spoon of cod liver oil. The taste was unforgettable, but the instinct behind it was sound: some fats really do matter. This Tuesday’s Supplement Spotlight looks at omega-3, the fats that have earned their good name, and at where a capsule fits beside the fish.

What omega-3s are

Omega-3s are a family of fats your body needs but can’t make enough of on its own. There are three main ones. ALA comes from plants. EPA and DHA come mostly from fish and seafood, and they’re the ones most research focuses on. Omega-3s form part of the walls of every cell in your body, and DHA is especially concentrated in the brain and eyes.

Your body can turn a little ALA into EPA and DHA, but only a small amount. That’s why plant and fish sources aren’t quite interchangeable.

Food first: where they come from

Oily fish is the richest source by far. Pilchards, sardines, mackerel, salmon, trout and herring all carry plenty, and tinned fish counts, which is kind to the budget. A tin of pilchards in tomato sauce on toast is about as humble, and as useful, as food gets.

For ALA, think flaxseed, chia seeds, walnuts, hemp seeds and canola oil. And here’s a lovely detail: fish get their omega-3 from the algae they eat, so algae oil is now a plant-based way to get EPA and DHA directly.

If you’d like a picture of what a regular fish habit might look like, What Happens to Your Body If You Eat Fish Twice Weekly is worth a read.

What the research suggests

Heart health. People who eat fish regularly tend to have healthier hearts, and that link is one of the more consistent findings in nutrition research. Whether capsules give the same benefit to people who are already well is less clear, and large studies have come back with mixed results. Higher amounts can lower blood fats called triglycerides, and that effect is well established.

Brain and mood. DHA is a building block of the brain, so the interest makes sense. Some research suggests omega-3s, particularly EPA, may help with low mood, but the results are mixed and far from settled. For memory in healthy adults, the evidence is thin.

Stiffness. Some studies suggest omega-3s may ease morning stiffness in people with inflammatory conditions of the joints. The effect, where it shows up, tends to be modest.

So the honest summary is this: eating oily fish has the strongest track record. Supplements have a place, but they’re more of a stand-in than a shortcut.

Who it may help

People who rarely eat fish. If fish just isn’t part of your life, whether through taste, budget or habit, a supplement is one way to fill the gap.

Plant-based eaters. Flax, chia and walnuts are wonderful foods, but they only offer ALA. Algae oil is the plant-based route to EPA and DHA.

Anyone whose eating has shifted. A move, a new routine, a season of eating on the run: it’s easy for fish to quietly drop off the menu. A supplement can hold the space while things settle.

Using it simply

Take it with a meal that contains some fat. It’s absorbed better that way, and you’re less likely to get fishy burps. Keep the bottle somewhere cool and dark, and in the fridge after opening if the label says so.

Give it a sniff now and then. A strong, sour or very fishy smell can mean the oil has gone off, and it’s time for a fresh bottle.

Fish oil, krill oil and algae oil can all work. When comparing, look at how much EPA and DHA the label lists, rather than the total amount of oil.

A few myths, gently set aside

“Fishy burps mean it’s working.” They usually mean it was taken on an empty stomach, or that the oil isn’t as fresh as it should be.

“Plant omega-3 is the same as fish oil.” ALA is valuable in its own right, but your body only converts a little of it into EPA and DHA.

“Cod liver oil and fish oil are the same thing.” Cod liver oil also contains vitamins A and D. Taken alongside a multivitamin or a vitamin D supplement, those can add up to more than you meant.

Looking after yourself

Keep to the dose on the label. Very large amounts aren’t better, and some research has linked high doses with an irregular heart rhythm in some people.

Omega-3s can affect how your blood clots. If you take blood thinners, let your existing care know before adding a supplement.

If you’re allergic to fish or shellfish, choose an algae oil or leave fish oil aside altogether.

Pick a reputable product that’s been purified and tested for freshness and for contaminants such as mercury.

Small and steady

You don’t need to overhaul your kitchen. A tin of fish once or twice a week, a spoon of ground flax on your oats, a handful of walnuts: these small things add up. If you’d like to go further, Healthy Fats: A Simple Guide to Choosing and Enjoying Them has more on choosing good fats for everyday meals.

If something doesn’t sit right once you start, pause it and please get it looked at; your body deserves that care.

You’ll find more like this on the Guides page.