Teaser, just do a quick search for "why do astronauts lose muscle mass", then read the stuff direct from NASA, you'll see what I mean by "they don't know any better". Also, straight from NASA, you can read that the fix they use (2 1/2 hours per day of exercise) doesn't actually work. Then another quick search for "what do astronauts eat in space". You'll see for yourself, my point of view is spot on.

Also, I did say "it's not an either or, it can be both", and I did say "it's only about load for NASA". I'm not arguing it's all about protein, I'm pointing out that NASA doesn't know any better. Put it this way, if you wanted to find out what the best diet for humans is on Earth, or wanted to find out what the best fix for muscle wasting disorders is on Earth, would you ask NASA?

You've heard of Biosphere 2, right? They learned a ton about diet and its effects on body/muscle mass. Never mind that they went in with a heavy bias for a plant-heavy diet. Granted, it's a closed system where a ton of variables can have an effect on our physiology so it's almost impossible to draw a firm conclusion on that, but diet is one of the top factors. If that's the only source of knowledge about diet and muscle mass, it's already enough to at least conclude that 2 1/2 hours of exercise per day as the only fix for muscle wasting in micro-gravity is literally a stupid idea. But look around, by far it's not the only source of knowledge about diet and muscle mass, so I'm not sure how to describe something worse than a stupid idea.

Now, if we also include the ton of knowledge you're talking about, for load and muscle mass, and we still decide that 2 1/2 hours per day should suffice, we really gotta come up with a better description than just "worse than a stupid idea".