Does your body convert alpha-linolenic acid into EPA and DHA?

Your body converts ALA only to a limited degree. Blood levels of EPA do rise with higher ALA intake, but DHA levels rise little or not at all. Seven out of ten intervention studies found no measurable rise in DHA after ALA supplementation. To achieve a comparable effect through ALA alone rather than through direct EPA/DHA intake, you would need more than 20 grams of ALA per day.

The reason is a bottleneck in the conversion process. An enzyme that carries out an early step works slowly and lets only a small fraction of the ALA through. The remainder is therefore never converted into the active forms your body needs.

Whether the conversion goes slightly better or worse also depends on who you are. Women under 50 convert ALA more efficiently, probably because of the influence of oestrogen. Smoking and a lot of excess weight in people who already have low omega-3 levels have a negative effect.

If you do not eat fish but still want to get EPA and DHA, algae oil is the most direct route. Three intervention studies showed that algae oil measurably raises DHA levels in the blood. Algae are also the original source from which fish obtain their omega-3s, so you simply bypass the fish. This works equally well for vegetarians and vegans.

There is also a plant-based fatty acid that skips the slow bottleneck step and is therefore converted to EPA more efficiently than ALA is. It is found in certain lesser-known plant species. Safe production and the right dosage have not yet been studied sufficiently, however, so it is not a practical option for now. What the precise health consequences of lower EPA and DHA levels in vegetarians and vegans actually are is also not entirely clear: their general health markers are favourable in studies, despite the lower levels.