Two omega-3s that do not replace each other, and two fish a week that do almost all the work.
Two kinds of fat hide behind the same name. ALA (alpha-linolenic acid) comes from plants: flax and chia seeds, walnuts, rapeseed oil. EPA and DHA come mainly from oily fish, sardine, mackerel, herring, salmon.
EPA and DHA are the ones doing the work in the body: DHA is a building block of the brain and the retina, EPA takes part in inflammation and clotting. The body can make EPA from ALA, but poorly, and hardly any DHA: tracer studies show limited conversion in men, somewhat better in women.
Hence the rule for reading the site: the ALA in a handful of walnuts counts, but it does not replace fish. The ω3 columns add up both kinds; on the Fish page, it is almost entirely EPA and DHA.
ANSES sets two separate benchmarks, precisely because one does not replace the other: 1% of calories as ALA, about 2 g a day for 2,000 kcal, and 500 mg a day of EPA and DHA, half each.
| To reach | All it takes is | Provides |
|---|---|---|
| 2 g of ALA | 30 g of walnuts | 2.7 g |
| 2 g of ALA | 10 g of ground flaxseed | 2.3 g |
| 500 mg of EPA + DHA | two portions of fish a week, one of them oily | 590 mg a day |
The calculation behind the last row: 125 g of sardine and 125 g of cod a week, spread over the days. That is the ANSES benchmark for fish, twice a week including one oily fish, and it is enough: the oily fish does almost all the work.
Whole, the flaxseed passes through the gut without opening, and its ALA with it. Ground just before eating, or bought as a powder and kept cold, it gives it up.
All omega-3s together, seeds come far ahead, with their ALA:
| Richest in the database | Per 100 g |
|---|---|
| Flaxseed | 22.8 g |
| Black chia seed | 17.8 g |
| Walnut (Grenoble) | 9.1 g |
| Mackerel in brine | 3.61 g |
| Sardine | 3.48 g |
| Mackerel | 2.59 g |
In EPA and DHA, the ones the body makes poorly, it is oily fish, the small ones first:
| Richest in the database | Per 100 g |
|---|---|
| Mackerel in brine | 3.36 g |
| Sardine | 3.1 g |
| Mackerel | 2.47 g |
| Herring | 1.75 g |
| Sardines in oil | 1.67 g |
| Red mullet | 1.62 g |
Small oily fish have another advantage, visible on the Fish page: low in the food chain, they build up little mercury, unlike bluefin tuna or swordfish.
Omega-6s, mainly the linoleic acid in sunflower and grapeseed oils, use the same enzymes as omega-3s. Too much omega-6 slows the conversion of ALA into EPA. ANSES therefore advises keeping the ratio between the two below 5, and everyday eating often overshoots it by far.
The ratio can be read food by food in the "Ratio ω6/ω3" column of the Seeds page: about 4.2 for walnuts, under 1 for flax, several hundred for sunflower. For oils, rapeseed is the best balanced of the common ones, see Fats & oils.
The simplest lever is not adding but swapping: rapeseed oil instead of sunflower for dressings, walnuts instead of peanuts with drinks.
Without fish, ALA is still easy to cover with walnuts, flax, chia and rapeseed oil. EPA and DHA are not: conversion is not enough to reach 500 mg. Eggs supply a little, especially those from hens fed on flax.
For vegans, there are DHA supplements made from microalgae, the source fish themselves get theirs from: fish do not make it, they eat it.
Two omega-3s, two sources: ALA from plants, EPA and DHA from fish. The first does not replace the others.
Two fish a week, one of them oily, cover the 500 mg of EPA and DHA; a handful of walnuts or a spoonful of ground flax covers the ALA.
Small oily fish, sardine, mackerel, herring, are the richest and the least loaded with mercury.
Less omega-6 helps as much as more omega-3: rapeseed rather than sunflower.
Benchmarks: ANSES, fatty acid intakes in France, and ANSES, PNNS benchmarks.
ALA conversion: Burdge et Calder, 2005.
Food composition: the Ciqual table from ANSES and the USDA FoodData Central database for US values.