> all these data come from nonhuman lab animals

Though what I have see so far is far from everything that could be learned from these surprisingly-humanlike mammals. Still need more research on timing. Maybe protein metabolism is not that different from the better studied methods of derailing glucose metabolism. Maybe the damage is set and done after any prolonged phase of inappropriate diet, and later minor adjustments in consumption have very little additional effect, after controlling for weight and caloric intake.

Maybe all humans need to do is watch their protein intake until puberty.. and then only 60 years later, as failing to retain muscle strength becomes more likely to kill them than any detrimental effect of excessive protein intake.