I've seen a rat study that alluded that when proteins were broken down, the muscles were taken last.
I've read opinion that stated that perhaps fasting is so health beneficial because of the bodies ability to choose "low use" proteins first. Thus eating up poorly constructed, weak or dying chains first, leaving the strongest to do their jobs, maybe even eating cancer etc
Anyone have opinions or better human studies that show and better explain this effect
Recent studies have been showing that the body can be very good at knowing which individual cells are the most damaged, and it is becoming clearer, esp. in the case of mitophagy that the cell can locally consume damaged parts of a single cell and reform those components anew.
When cells are broken down, they are not immediately ejected (or excreted) from the body, they are the perfect building material for whatever new cells are needed. They are also in a ready state to be used a fuel.
A great free-to-read review on autophagy across many cell types is Nature. 2008 Feb 28;451(7182):1069-75. Autophagy fights disease through cellular self-digestion.
One of the items that I find extra applicable to my Primal Sprinting practice, is that brief metabolic stressing (Yay for brief sprints or metcon) seems to trigger the mitophagy (deconstruction) of the least efficient mitochondria in each stressed cell, followed immediately by the construction of copies of the more efficient mitochondria remaining in the cell... I think this is only one of the reasons why sprinting or quick metcon can have such rapid results for increased capacity.
Maybe you are alluding at least in part to autophagy, the breaking up of damaged cells back into usable amino acids. Ketosis stimulates this, as shown here. I don't know how much protein this process will spare, though.
I love love LOVE this thread... I've wondered the same thing Stephen-Aegis...
Protein is such a coveted material in mammalian systems and nothing is wasted from the kidney and organ standpoint - all protein is re-filtered and recovered to prevent excretion. Kidney failure patients cannot retain protein -- and they are j*cked. In the environment, protein (meat/seafood) and omega-3 are relatively scarce and when humans learned to take advantage of these two, their brains emerged with consciousness, art, culture and global domination. Only the 'gut' can sense the abundance of protein and omega-3 in the environment (perhaps the sense of vision/smell in the brain) thus these receptors for amino acids and fatty acids (PPAR) control and regulate the instestines for the overall immunity and health.
Autophagy appears to me like recycling and I think the mitochondria very good at it, since they may be the most important generators of energy and regulators of systemic energy.
This may not address the core of your question but we lose protein and rebuild daily (during sleep...that's when we become BIONIC). If one wears a cast on the arm, the arm muscles will break down. Demand, genetics (myostatin) and perhaps diet control to what degree, I would imagine but I don't know for sure.
What I suspect is what the proteins someone consumes may have a bigger effect than we consider. Methionine -- apparently VERY CRITICAL to health, bowel immunity and antioxidant status. The studies below review it. The first gave a methione-deficient diet and quickly ruined the antioxidant status (glutathione) and gut lining (small instestinal villus atrophy, proliferative crypt cells, etc) and body weight gain decreased in neonatal pigs compared with controls.
Methionine is only find in meat, seafood and dairy in any meaningful amount. Beans and plants have almost none.
What you're describing is probably a very simplified version of what's happening. If you link the rat study you've described, we can go from there.
Protein synthesis and breakdown is a futile cycle, with both constantly happening at different rates. "Anabolism" is simply when the synthesis out paces the breakdown, and "catabolism" vice-versa.
It's likely the structures that are being degraded have defects or are undesirable for some reason, and the excess amino acids from that process serve to fuel the amino acid based GNG.
I have not reviewed any research on this subject, but burn victims would be a good place to start as there is quite a bit of literature on the catabolism they experience post trauma.