Flip the bottle over before you buy fish oil

Pick up a standard bottle of fish oil and look at the small print, not the big number. The front says 1,000mg. Turn it round and you'll usually find that each capsule contains about 180mg of EPA and 120mg of DHA. Those two are the omega-3s people are actually buying. The other 700mg is fish oil that isn't doing the job you think you're paying for.

So a "1,000mg" capsule is really a 300mg capsule. Two a day gets you 600mg. That's the first thing worth knowing, because it changes the comparison completely.

A tin of sardines does more than that. So does a piece of mackerel, or a decent fillet of farmed salmon. Oily fish is dense in EPA and DHA in a way that generic capsules are not, and it comes with protein, selenium, iodine and vitamin D attached. If you're eating two proper servings of oily fish a week, you are almost certainly in the range that public health bodies in the UK and the US point at, and the bottle in the cupboard is redundant.

What counts as oily fish, and what quietly doesn't

Salmon, mackerel, sardines, herring, kippers, trout, anchovies, sprats. Fresh tuna counts. Tinned tuna, for the most part, does not — the oils are largely lost in processing, which is why a tuna sandwich is a fine protein choice and a poor omega-3 one.

Cod, haddock, pollock, prawns, tilapia: good food, low in EPA and DHA. Battered cod on a Friday is not the two servings.

The practical version of the guidance is boring. Two dinners a week where an oily fish is the main event. That's it. Salmon in a traybake with potatoes and broccoli. Mackerel fillets grilled for four minutes a side. A tin of sardines mashed onto toast with lemon, a scrape of mustard and too much black pepper, eaten standing up at the counter on a Tuesday while the children work their way through pasta they'd eat every night if you let them.

That last one is the whole trick, honestly. You are not going to cook two separate fish dinners a week for people who don't want fish. You will eat a tin while they eat something else, and you'll have solved it in four minutes with nothing to wash up.

When a supplement earns its place

Some people genuinely won't eat fish. Not "prefer not to" — won't, ever, and no amount of lemon and chilli is going to change it. Others can't, because of allergy. If you're in that group and you also don't eat much in the way of walnuts, flaxseed or rapeseed oil, a supplement is a sensible way to cover a gap.

Pregnancy and breastfeeding come with their own guidance, including which fish to limit. That's a conversation for your midwife or GP, not an article.

And if you've been told by a doctor to take a high dose of omega-3 for a specific reason, take what you've been told to take. That's a prescription decision, not a supplement-aisle one.

Outside those cases, the honest answer is that a capsule is insurance against a diet you could fix at the fishmonger's counter instead.

Don't expect it to fix your training

Omega-3 gets sold hard to people who lift. Less soreness, better recovery, joints that stop grumbling. The effects people report are, at best, modest. Nothing about a capsule will compensate for six hours of sleep and skipped meals.

If your elbows hurt and you're training four days a week on a bad diet with a toddler waking you at five, the fish oil is the least important variable on the list. Fix the sleep window. Eat enough protein. Then, if you like, add the fish.

I'd rather you spent the same money and attention on getting oily fish onto the table twice a week, because that change also improves the dinners, which is not nothing when you're feeding a family.

How to buy it without getting stung

If you do buy it, buy properly.

• Read EPA + DHA per serving, then check what a serving is. Plenty of bottles quote their best number for three capsules. A 90-capsule bottle at three a day is a 30-day supply, not three months. Work out the cost per gram of EPA and DHA, not the cost per bottle. Concentrated oils often win on that maths even when they look expensive on the shelf.
• Smell it. Fish oil oxidises. Rancid oil smells sharply fishy and slightly of paint. Snip a capsule open when you get home. If it's foul, take it back. Persistent fishy burps are usually the oil, not you.
• Buy the smaller bottle. A 12-month supply spends nine months going off in a warm kitchen cupboard. Keep it in the fridge, or the freezer if you want to be strict, and away from the window.
• Check the date, and check the form. Triglyceride-form oils are generally better absorbed than ethyl esters, and cost more. Whether that's worth paying for is a judgement call, and the difference is smaller than the marketing suggests.
• Don't double up by accident. Cod liver oil is a different product, carrying a lot of vitamin A, which accumulates. Some multivitamins already contain omega-3. Adding three products together is how people end up taking far more of something than they intended.
• Algae oil exists. It supplies DHA and EPA directly without the fish, which matters if you're vegetarian or the smell is a hard no. It costs more per gram.

The bits people skip

Mercury and other contaminants are a reasonable concern, and the sensible response is variety plus a bias toward small fish. Sardines, anchovies and herring sit low in the food chain and are cheap. Species like swordfish, marlin and shark come with limits attached, especially for children and anyone pregnant. Check the current national guidance rather than taking my word for the specifics, because it gets updated.

High doses of omega-3 can affect bleeding. If you're on an anticoagulant, or you've got surgery coming up, or you're taking anything that your pharmacist has warned you about interacting, ask them before you start. They'll answer in two minutes and they won't charge you.

One more thing, and it's the one people resist. If you eat fish twice a week and you're still buying fish oil because it feels responsible, that's not nutrition. That's a habit with a receipt.

Buy a tin of sardines instead. Eat it on Tuesday.