There are probably more myths about protein than about fats. That's saying a lot, given the hoopla about fats this society has been facing the past several decades.
I don't claim that the below excerpts are "right" or "wrong", I only provide them here to stimulate discussion.
The following is a paraphrase from Mark Twight's Extreme Alpinism, cf. p. 66:
The current recommendation (by USDA) is 0.8 g protein / kg body weight / day. Twight claims that this is inadequate for a hard working athlete, who might require 2.5X that amount (typical endurance athlete participating in hiking/backpacking, maybe 1.5 to 2.0X that amount). Why? Prevent the body from dipping into protein stores (muscle mass) to access caloric reserves when running at a metabolic deficit. The term: protein cannibalism. The result: not a smart strategy for an endurance activity, such as an adventure race, expedition alpine climb, or thru-hike.
Here's the kicker: eating excess protein won't improve performance, because the of the metabolic max for conversion of protein to muscle, and the excess is converted to carbs, fats, or excreted. The demand for protein: directly related to your muscle mass. Big muscles you got, big protein you can use, and vice versa.
Another nugget found in Twight's book, that's not a secret among endurance athletes, is the ability for protein to kickstart glucose metabolism and increase its effiency.
Endurance athletes know well the 'bonk' that occurs several hours into a race, climb, hike, etc. Especially acute is this bonk among those that focus their caloric intake on carbo gels and drinks. When you hit that wall, you think, "oh, I need more gel" and, well, guess what, it doesn't work, at least, not quickly.
So, the savvy endurance runner pulls out his Slim Jim pepperoni stick and within a few minutes, is rockin' and rollin' again. Why? (Theory follows) The rapid metabolism of the protein releases chemical signals to the rest of the body that tells it "hang in there buddy, more is on the way", and the next carbo gel that goes in the body is rapidly metabolized, and zoom, you've blown through the wall like it was nothing.
There's been a bit of research on this phenomenon, and the last time I looked into it about a year ago, no consensus regarding the mechanism could really be reached, although virtually everyone agreed that the phenomenon existed, suggesting that protein plays a huge role in metabolic stabilization, which has a net effect on increasing metabolic efficiency and regulating the engine, so to speak.