lol--thanks, Dan. I'm so at the edge of my own knowledge here, my head hurts (like doing little neural pushups until failure ). I've looked on-line at more complicated stuff than the undergrad A&P I'm taking, and perhaps the answer lies in the Krebs cycle itself. Inside the mitochondria at some point, in converting pyruvic acid and oxygen and glucose to ATP (and all that other crap), there's a moment where ketone bodies play a role. Is the membrane of both the cell itself and then the mitochondria perhaps permeable to ketones in our bloodstream, so they somehow jump in and add to the Krebs cycle? Uhhhhh. Probably not, but insofar as I did not/did understand what I was reading, that was my only guess.

I can't even find a good cellular explanation of how protein and fat get converted to ATP, though I know it happens.

The problem with trying to research this stuff is that the "ketones are evil" mindset is all over physiology books...so it's hard to dig under it to the possible truth.

Nat, to answer your PM yes, red/white muscle fibers/cells are same as slow/fast twitch. Red because of oxygen, white because of the lack of it. Red ones use aerobic processes to create most of their ATP to do their contractile thing; white ones use anaerobic processes and can't work very long because of that...they run out of ATP, so no myson crossbridging, no opening of calcium ion channels in the SR, no more contractions possible.