Propionic Acid and Lethargy/Brainfog


Senior Member
A few weeks ago I started getting severe lethargy and brainfog from fermentable fibres. Oat, chia, pectin; all nasty now. I suppose this explains my reaction to onions too, since they are rich in fermentable fibre. Of the three short-chain fatty acids produced from fibre in the colon, I think propionic acid (PA) is the most likely culprit. Someone else here complained about PA causing lethargy and brainfog.

Most PA gets converted to glucose in the liver, but elevated PA in the brain is known to cause lethargy. It's metabolized in mitochondria in glial cells and some neurons, a process involving B12. One model involves GABA accumulation in neurons.

I come up with any detailed theory for why PA should be affecting me so strongly now, after all those years of fibre that didn't bother me. It could be a gut or microbiome change that has increased my serum PA. It could also be an increased sensitivity of some brain cells to still-normal levels of PA.

I think it's interesting that (what I assume is PA) causes some of the same symptoms that ME does. I'm posting this as 'something to consider' for those of us who try to puzzle out ME. Maybe some researcher will read this and have some 'Maybe that would explain <whatever>' moment, or at least have PA in mind while thinking about ME.

I'm just hoping that this is a temporary issue, and it will go away like some of the other sensitivities did. Carbs in the afternoon/evening without fibre give me insomnia. I did chew up and swallow some paper, and that did seem to block the insomnia, but it takes considerable effort to render it into finely divided pulp. I'm considering boiling wheat bran in sodium carbonate solution to remove the hemicellulose.

I can't think of anything that might have triggered this change.