In a recent post by u/exfatloss about the half life of seed oils, he talked about the different benefits we can expect after cutting them out for extended periods. It was a great post, but I found myself coming away unsatisfied with the explanation given for why seed oils are bad:
Every cell in your body is surrounded by a membrane. That membrane is made of a double layer of phospholipids, with cholesterol sandwiched between them.
He goes on to say that if you feed your body PUFAs which are unstable and easily oxidized (damaged), your body will use these to build the membranes of your cells and then those cells will be easily damaged causing all the problems that arise from that (chronic and auto-immune diseases).
This makes a lot of sense to me intuitively, but I find myself thinking: if this were true, surely it would be common knowledge by now? Wouldn’t the scientific community have sounded the alarm long ago? Why has society not shifted to celebrate animal fats and abolish seed oils? It almost seems too simple.
So I’ve been reading the literature and trying to work it out. This is my best attempt at summarising what I’ve found so far:
P1: Dietary intake of PUFAs cause increased levels of PUFAs (specifically Linoleic Acid (LA)) in cell membranes1, tryglycerides and cholesterol.23
P2: Excess PUFAs are a precursor to Oxidized Linoleic Acid Metabolites (OXLAMs).4
P3: LA conversion leads to the formation of free radicals.5
P4: LA can also be further metabolized into arachidonic acid (AA) which is a precursor to oxidized AA metabolites (OXAAMs), including 5-, 8-, 9-, 11-, 12-, and 15-hydroxy-eicosatetraenoic acid (HETE).6
P5: Increased levels of OXLAMs, OXAAMs and free radicals are mechanistically linked with diseases.7
From all of these it follows that:
C1: Because our body can’t synthesise LA, lowering dietary intake will lower the levels in the body and heal the associated diseases with enough time.
This is essentially what u/exfatloss said in his article, just with bigger words.
As far as I can tell, each step of this process has evidence supporting it, but nobody has put them all together with the emphasis that they seem to warrant.
If seed oils really are causing all these chronic diseases, and we have evidence for each step in the process, this might be the worst mistake in the history of human nutrition.
Which brings me back to my question: why isn’t this common knowledge? There are lots of possiblilities. Right now the most obvious and likely one is just that I’m wrong. I’m missing some evidence or misinterpreting some results. So I’m going to keep researching and expanding on each link in the chain, trying to piece together the story as I go and figure out where I’m wrong.
Incorporation of 13-hydroxyoctadecadienoic acid (13-HODE) into epidermal ceramides and phospholipids: phospholipase C-catalyzed release of novel 13-HODE-containing diacylglycerol: “both [14C] Linoleic Acid and [14C] 13-HODE are markedly incorporated into phospholipids, particularly, phosphatidylcholine (PC) and phosphatidylinositol (PtdIns)”
Lowering dietary linoleic acid reduces bioactive oxidized linoleic acid metabolites in humans: “OXLAMs are readily incorporated into, and released from, esterified lipid pools including phospholipids, tryglycerides and cholesterol esters.”
Oxygenation of lipoproteins by mammalian lipoxygenases: “More than 90% of the oxygenated polyenoic fatty acids were found in the ester-lipid fraction, particularly in the cholesterol esters”
OXLAMs include: 4-Hydroxynonenal (HNE), 9-hydroxy-octadecadienoic acid and 13-hydroxy-octadecadienoic acid (9- and 13-HODE); “these two hydroxy metabolites are enzymatically oxidized to their keto metabolites, 13-oxo-octadecadienoic acid and 9-oxo-octadecdienoic acid.” [source]