[alexholehouse]

Short chain fatty acids can be things like acetic acid, propionic acid, butyric acid. The fermentation process takes in fiber and puts out these guys, so while fiber isn't an SCFA polymer, I don't think this statement is inaccurate (i.e. I don't have the metabolic pathways off hand but these could be direct breakdown products given the shortness of the carbon chains - acetic acid almost certainly is.)

[gus_massa]

I mostly agree.

The main path for glucose involves splitting it in two 3 carbon molecules, mainly pyruvate https://en.wikipedia.org/wiki/Glycolysis From this it's easy to make acetic acid (2 carbons), like the acetic acid in vinegar. And , I guess it's also not very difficult to make propionic acid (3 carbons).

I can accept that they say that fiber or glucose is "break down" to acetic acid, propionic acid, but I think it's misleading. (And the usual definition of fatty acid starts at 4 carbons https://en.wikipedia.org/wiki/Fatty_acid )

I had to search for the pathway to produce butyric acid (4 carbons). The main path is apparently splitting the glucose in pyruvate and adding a carbon to it, so it's not a direct break down. But there is an additional pathway, with glutaric acid, that perhaps may qualify, but I'm not convinced. https://en.wikipedia.org/wiki/Butyric_acid http://mbio.asm.org/content/5/2/e00889-14/F1.expansion.html

[SomeStupidPoint]

I think they're using it colloquially: you can "break down" trees in to paper, even though the paper technically requires reassembly and further processing from the most deconstructed tree step.

But it is a phrase that the average layperson would take as "simpler things made from the raw ingredients by the processors", rather than a direct deconstruction pathway.

It's a common problem when technical language collides with a common term or phrase, because most articles will mean the common one and send pendants in to a fit.

[spangry]

I think this is the crux of the issue. If one ascribed to the prion hypothesis, than ketogenic metabolism would almost certainly have to be related to higher probability of prion formation, and more survivable conditions in vivo.

Another common way some AAs are metabolised is by hydrogenation is red blood cells. So I think this eats up a hydrogen ion at the very least, leading to greater intra-cellular oxidisation and a messed up blood plasma pH, increasing the occurrence of abnormal enzymatic reactions. The metabolites you mentioned are present in much larger quantities on low carbs, due to increased synthesis and use of proteins for energy, including for the brain...

Oh and at least a few of those metabolites sometimes ultimately metabolise to acetone, especially if normal metabolism disrupted by wonky pH balance.

Anion gap in soft tissue cells may also explain 'twitches': spontaneous muscular activation due to soft tissue cell hyper-natremia (unbalanced towards sodium).

Crazily, excess acetone restoration is one theory that explains spontaneous human combustion (acetone is quite volatile and flammable)...

[spangry]

Damn auto-correct. That should be "acetone respiration".