Omega-3: What It Is, How Much You Need a Day and Which Foods Have It

When people talk about omega-3 they lump together three fats that the body does not use in the same way. It is worth separating them before looking at how much you need and where each one comes from.

EPA, DHA and ALA: three different fats

How much omega-3 is recommended

EFSA sets an adequate intake for adults of 250 mg a day of EPA + DHA, a figure aimed at cardiovascular prevention: in the studies it reviewed, eating oily fish or taking the equivalent of 250-500 mg a day was associated with fewer deaths from coronary heart disease. During pregnancy and breastfeeding it proposes adding 100-200 mg of DHA to those 250 mg. For ALA, the reference is 0.5% of energy: around 1.1 g a day if you eat 2,000 kcal. Since fish is not eaten every day, it helps to think in weeks: 250 mg a day is about 1,750 mg a week.

How much omega-3 each food has (mg per serving)

Values from USDA FoodData Central with typical servings. The fish is cooked or canned and drained, which is how it is eaten:

Two details change the maths. Canned light tuna has almost ten times less than salmon (220 versus 2,150 mg per 100 g), so it should not count as oily fish as far as omega-3 is concerned. And in these USDA data, farmed salmon does not have less omega-3 than wild salmon: 2,150 versus 1,840 mg, although it varies with the feed. With two servings a week of salmon, mackerel or sardines you go past the 1,750 mg a week. If you want to check the calories of other foods, there is the food calorie table.

Why walnuts do not replace fish

ALA is the starting point from which the body can make EPA and DHA, but it does so inefficiently. In a study using isotope-labelled ALA, young women converted about 21% to EPA and 9% to DHA (Burdge and Wootton, 2002); in another with young men, conversion to DHA was very low or absent (Burdge, 2002). They are small studies with few people, but they point in the same direction, and the authors suggest that the greater capacity in women may help meet the DHA demands of pregnancy. The practical conclusion: walnuts, flaxseed and chia count as ALA, but if you eat no fish or seafood, the direct source of DHA is algae oil.

What the large capsule trials found

Eating fish and taking capsules are not the same thing, and supplement trials have produced more modest results than the label promises:

• VITAL (2019): 25,871 US adults without cardiovascular disease took 1 g a day of omega-3 or placebo for a median of 5.3 years. Major cardiovascular events (heart attack, stroke or cardiovascular death) and cancer did not go down; a secondary analysis showed fewer heart attacks, a finding that needs confirmation.
• ASCEND (2018): 15,480 people with diabetes and no cardiovascular disease took 1 g a day for an average of 7.4 years. A serious vascular event occurred in 8.9% on omega-3 and 9.2% on placebo, with no significant difference.
• REDUCE-IT (2019): 8,179 people with cardiovascular disease or diabetes and high triglycerides despite a statin took 4 g a day of icosapent ethyl, a purified EPA drug. Events fell from 22.0% to 17.2% (25% fewer in relative terms), although there were more hospital admissions for atrial fibrillation (3.1% versus 2.1%).
• The REDUCE-IT caveat: the placebo was mineral oil, and in that group LDL cholesterol rose 10.9% and C-reactive protein 21.9% in the first year, while on the drug they barely changed (Ridker, 2022). Part of the difference may be due to the placebo making things worse. In STRENGTH (2020), with 4 g a day of EPA + DHA versus corn oil in 13,078 high-risk patients, there was no difference (12.0% versus 12.2%).
• The 2020 Cochrane review (86 trials, 162,796 people) concludes that increasing EPA and DHA has little or no effect on total mortality and cardiovascular events, and may slightly reduce coronary deaths: 334 people would need to be treated to prevent one. What it does do, with high certainty, is lower triglycerides by about 15%.

None of this means omega-3 is useless: it means that, for a healthy person who already eats some fish, a daily capsule has not been shown to prevent heart attacks or strokes. High doses for very high triglycerides are a treatment prescribed by a doctor. If your triglycerides are high, start with how to lower triglycerides with diet.

Mercury: which fish to limit

Salmon and small oily fish (sardines, anchovies, mackerel) are in the low-mercury group of AESAN, the Spanish food safety agency; the ones that accumulate most are the large predators. AESAN recommends:

• General population: 3-4 servings of fish a week, of any species, alternating white and oily fish.
• Pregnant women, women planning a pregnancy or breastfeeding, and children aged 0 to 10: avoid swordfish, bluefin tuna, shark (dogfish, mako, blue shark…) and pike, and eat 3-4 servings a week of the rest.
• Children aged 10 to 14: limit those four species to 120 g a month.

The simplest way to cover your omega-3 is on the plate: two servings of oily fish a week exceed, on average, the 250 mg a day that EFSA sets. If you want to check, log it for a few weeks with Renzy.