Again via twitter, Tucker retweeted a thread which included the link to this paper
Increased EPA levels in serum phospholipids of humans after four weeks daily ingestion of one portion chicken fed linseed and rapeseed oil
Over the years I keep coming back to this plot
which comes from another paper:
It shows, very clearly, that in rats both linoleic acid and alpha linolenic acids are equally efficacious at suppressing the conversion of ALA to DHA. Given 1% of energy in the diet as ALA then copious amounts of DHA are produced, just so long as the LA proportion of calories is less than 2% of the total. Never mind the ratio. Avoiding PUFA will generate DHA from ALA provided a basic minute minimum of ALA is present in the diet, somewhere around 1% of calories. Over at the right hand side of the plot we can see that even drinking 12% of your energy intake as ALA will not generate significant DHA if you are up in the cardiological nirvana of 16% of energy as LA.
That is in rats.
Chickens superficially appear to be somewhat different.
Switching from soybean oil to a rapeseed/linseed oil mix in the diet increases DHA in the breast meat. Soybean oil gives 14% of lipid as DHA, rapeseed/linseed gives 21%. Of not very much fat in breast meat so the amounts are small in total, but still highly statistically significant.
So ALA in food bumps up DHA in muscle. Of chickens.
This is what the chicken diet looked like, with annotation to give the fat percentage of total calories and the LA and ALA percentages of total calories in the diet, crudely:
We can overlay the chicken diet very approximately, on the rat plot to get this:
which, not surprisingly, suggests that the DHA production in the "high" ALA diet (blue) is actually more influenced by the reduction in LA. At 4% LA we could equally have had ALA at 1% of calories and still got a lower value for DHA than we did by having LA down at 2% of calories.
Might this work for humans too? Could adding ALA to our diet improve DHA availability, with all of what that entails for improved brain development and cognitive function. Just by avoiding LA and maybe drinking a little (traditional) varnish? The study didn't ask this. Instead they fed the above chicken to some humans. Either omega 3 enriched or omega 6 enriched.
This actually dropped DHA in the participants' plasma phospholipids in both groups. Admittedly not by much, so the change was neither statistically nor biologically significant. But it dropped. I would hazard a guess that the chicken simply displaced a richer source of ready-formed DHA from the diet, the tiny amount in the breast meat would do nothing per se. I believe Norwegians consume a certain amount of fish, unless they're given free chicken to eat.
The rise in EPA must have made the authors happy that something positive came from all of that work. But I don't think you can build a brain out of EPA, DHA looks to be the molecule for that.
Ultimately pre-formed DHA does not look to be necessary for brain development if you have a modest supply of ALA from (grass fed, possibly large) animals and avoid consuming significant amounts of LA. This appears to hold true for rats, chickens and I expect for humans.