I spent a Sunday morning last month lining fourteen fish oil bottles on my kitchen table and reading the back labels like a tax form. Eleven of them said “1,000 mg fish oil” in huge type. Only four told me, in much smaller print, how much of that was actually EPA and DHA. That gap is the whole story, and it’s why two people can take the same “dose” and get completely different results.
So let’s do the math the bottle usually skips. And then talk about the one thing fish oil genuinely does well, plus the two things it keeps failing at in big trials.
The three omega-3s your body actually cares about
Omega-3 is a family, not a nutrient. Three members show up on labels:
- ALA (alpha-linolenic acid) – the plant one. Walnuts, chia, flax, canola.
- EPA (eicosapentaenoic acid) – the marine one, and the one behind most of the triglyceride and inflammation research.
- DHA (docosahexaenoic acid) – structural. Your retina and brain tissue accumulate it, which is why it matters most before birth and in pregnancy.
Here’s the part nobody prints on the front. Your body can convert ALA into EPA and DHA, but it does it badly – roughly 5 to 10 percent becomes EPA and under 5 percent becomes DHA, depending on the study and on who you are. So a tablespoon of ground flaxseed (about 2.3 grams of ALA) is not the same metabolic event as a can of sardines. Both count. They just don’t count the same way.
How much you need, by goal
The US National Institutes of Health sets an adequate intake for ALA only: 1.6 grams per day for men and 1.1 grams for women. There is no official RDA for EPA and DHA, because the evidence supports ranges by goal rather than one universal number. The table below is the one I actually use when someone asks me “how much should I take?”
| Goal | EPA + DHA per day | Realistic way to get it |
|---|---|---|
| General maintenance | 250-500 mg | Two servings of fatty fish a week, or one standard softgel |
| Lowering high triglycerides | 2,000-4,000 mg | Prescription-grade concentrate; clinician should own the dose |
| Pregnancy and lactation | 200-300 mg extra DHA | Low-mercury fish or a DHA-specific prenatal |
| Dry eye, joint comfort | 1,000-2,000 mg | Mixed evidence; give it 8-12 weeks before judging |
| Post-heart-event secondary prevention | 1,000 mg (mostly EPA at Rx dose) | Discuss with your cardiologist, not a pharmacy aisle |
What’s actually in the food
Supplement labels are honest-ish about milligrams. Food is free and clearer. Here’s EPA plus DHA per 3-ounce cooked serving, the numbers I check before recommending a diet change over a bottle:
| Food (3 oz cooked unless noted) | EPA + DHA |
|---|---|
| Mackerel, Atlantic | about 1,700 mg |
| Salmon, farmed Atlantic | about 1,750 mg |
| Anchovy, canned in oil | about 1,400 mg |
| Sardine, canned | about 1,300 mg |
| Rainbow trout, farmed | about 1,100 mg |
| Herring | about 1,000 mg |
| Cod | about 200 mg |
| Tuna, canned light | about 150 mg |
| Shrimp | about 120 mg |
| Eggs, omega-3 enriched (2 eggs) | about 70 mg |
| Walnuts (1 oz, ALA only) | about 2,500 mg ALA |
| Chia seeds (1 oz, ALA only) | about 1,780 mg ALA |
Notice the trap in the last two rows. A bag of walnuts looks like the highest omega-3 food in the shop until you remember the conversion ceiling. And notice the other trap: canned light tuna, the default “healthy” choice in a lot of lunchrooms, delivers about 150 mg. Two cans a day still leaves you short of the maintenance range.
The capsule math nobody does for you
A standard softgel holds 1,000 mg of fish oil. Most of those capsules contain roughly 180 mg EPA and 120 mg DHA – 300 mg total, or 30 percent of the pill. The other 700 mg is fat that isn’t doing the job you bought it for. Read one label this way and the marketing changes shape: “1,000 mg fish oil” and “300 mg omega-3” are the same product in two fonts.
To reach 2,000 mg of EPA plus DHA from that capsule you’d swallow nearly seven softgels a day. Concentrates change the arithmetic: a triglyceride-form concentrate can run 600 to 700 mg per gram, so two capsules get you there. Price per gram of actual EPA plus DHA – not per capsule, not per bottle – is the only honest comparison. I now do that division in the store, and it has saved me from two very pretty bottles.
When fish oil doesn’t help
This is where I get pushback, so I’ll be blunt. Fish oil reliably lowers triglycerides – roughly 15 to 30 percent at 2 to 4 grams per day, and that finding is solid and dose-dependent. But for preventing heart attacks in otherwise healthy people, the big trials are lukewarm:
- VITAL followed 25,871 people on 1 gram a day and found no significant reduction in major cardiovascular events overall.
- ASCEND, in 15,480 adults with diabetes, found modest benefit on some endpoints and no clear overall effect.
- A 2018 Cochrane review of 86 trials concluded that raising EPA and DHA lowers triglycerides but does little to change heart-attack risk.
Two honest conclusions follow. If your triglycerides are high, the dose is a medical decision, not an aisle decision. And if you’re otherwise healthy and hoping a generic capsule will do the work of an actual diet pattern, the evidence doesn’t support that bet – the food matrix, the replaced processed meat, the fibre: that’s where the effect lives. If you want the broader picture on lipids, our guide on how to lower cholesterol naturally covers what moves the numbers and what merely looks busy.
Six things I check before buying
- Total EPA plus DHA per serving, not “fish oil” per capsule. If the number is missing, walk.
- Form. Triglyceride form and re-esterified triglyceride form absorb better than the cheap ethyl ester.
- Oxidation. Cut one open and smell it. Rancid oil smells like old paint, not the sea.
- Source. Small fish (anchovy, sardine, mackerel) accumulate less mercury than swordfish or big tuna.
- Third-party testing. IFOS, USP or NSF on the label – not a house brand seal.
- Storage. Fridge after opening; heat is what turns oil into the thing you were trying to avoid.
What I actually do
Two cans of sardines most weeks, salmon when it’s on sale, and one concentrate capsule on the days fish doesn’t happen. I keep the bottle in the fridge door. I stopped buying the 1,000 mg bottles once I understood the 30 percent problem, and I stopped expecting a capsule to outwork a plate. If you’re also juggling other supplements, the same label-reading habit applies – we wrote a plain comparison of magnesium glycinate vs citrate vs oxide for exactly that reason, and the vitamin D maths is in how much vitamin D you actually need.
One more thing worth doing instead of buying: track something you can measure. Resting heart rate is free and it moves when the rest of your habits do – our piece on how to lower your resting heart rate naturally walks through the numbers people actually see.
Evidence note: Figures above come from the NIH Office of Dietary Supplements omega-3 fact sheet (ALA adequate intakes, food composition), the American Heart Association’s two-servings-per-week guidance, and the VITAL and ASCEND randomised trials plus the 2018 Cochrane review of 86 trials. None of it replaces a conversation about your own lipid panel – dose and form change with your numbers, your medications and whether you’re pregnant.