Alpha-linolenic acid (ALA)
An essential plant-based omega-3 fatty acid (flax, chia, walnuts, rapeseed), the precursor of the long-chain omega-3s EPA and DHA, but with limited conversion.
ALA is the only omega-3 that is essential in the strict sense: the body cannot make it, so it has to come from plant foods. From ALA, the body can in theory synthesise the long-chain omega-3s EPA and DHA (the most active forms).
The original angle (conversion, the Achilles heel of plant sources): the central problem: the conversion of ALA → EPA → DHA is very inefficient in humans:
- ALA → EPA: only ~5 to 10%
- ALA → DHA: often < 1 to 5%
This conversion depends on several factors: sex (women convert better thanks to oestrogen, an advantage for pregnancy), hormonal status, age, and above all the omega-6/omega-3 ratio (too much omega-6 “saturates” the shared conversion enzymes).
Major practical consequence: eating flaxseed or chia seeds supplies ALA and is beneficial, but does not guarantee a good DHA status (crucial for the brain and retina). Vegans and people with poor conversion should consider a direct source of EPA/DHA: algae oil (a direct plant source of DHA, the very one from which fish get their omega-3).
ALA’s own benefits: beyond its role as a precursor, ALA has its own beneficial effects (cardiovascular in particular) shown in several studies.
The oxidation trap: ALA is highly polyunsaturated and therefore fragile. Flaxseed oil oxidises quickly: keep it in the fridge, away from light, use it raw (never heated) and soon after opening. Flaxseeds should be ground just before eating (whole, they pass through the gut without releasing their omega-3).
Sources: flaxseeds (ground), chia seeds, walnuts, rapeseed oil, camelina oil, purslane.