Of course there are myriad factors at play here and the landscape is littered with recommendations from supplements manufacturers - some of which simply do not stack up under closer scrutiny.
The fear that muscle will melt away in the absence of consistent protein overloading is one such prevailing - and powerful - myth.
So is there a bottom line, and if so what is it?
If you're fat adapted, or headed that way, protein is important to the extent that you want enough, but not enough to hinder your fueling objectives. In simple terms, protein will behave like a "semi carb" and consuming too much may trip you off the fat burning tightrope.
In this context, there is a balancing act to be done for any endurance athlete striving to maintain an optimal fat fueling strategy. When Phinney & Volek refer to a "well formulated ketogenic diet" this is one of the key points they are getting at.
The study below hypothesized that "higher dietary protein content would attenuate the decline of anabolic hormones and, thus, prevent losses of fat-free mass." It did not. Surprise, surprise!
We have also seen lean muscle - and performance - preservation after 30 days of a well formulated ketogenic diet protocol in elite gymnasts (more on that here). However tempting it might be to put forward the case that fat is the key macro for muscle retention, that would be the flip side of the very same mistake the protein brigade have been making.
Protein and Fat are the essential building blocks of human health and theirs is a Marriage made in Muscle. It is becoming increasingly clear that it is the dance between these 2 mighty macros we must get right. In isolation, neither will get you all the way there.
The 2006 study below raises some interesting theories about muscle preservation on a low carb diet but the Dietary Protein commentary raises that key question again - How much Protein is right for me?
Some recent research has been pointing to the increased efficacy of high quality whey protein versus alternative sources, particularly as we age, so if you are fond of a protein supplement, keep it whey and keep it clean.
That said, your dollars would probably be better spent pairing up a selection of high quality fats (coconut oil, grass fed butter, EV olive oil, lard) with quality real food protein sources including pasture raised meats. That way, you know you're ticking both boxes.
The upshot? When it comes to retention of lean muscle mass, behind every good protein, there's a great fat!