[lemming]

Yeah, 3.3g/kg is really high, and I don't see how you could get there without living on shakes. From that examine.com article:

Eating more than 2.6 g/kg (1.18 g/lb) is probably not going to lead to greater muscle gains, but it can minimize fat gains when “bulking” — i.e., when eating above maintenance in order to gain (muscle) weight.

There doesn't seem to be a lot of evidence for the kidney thing as long as you don't dramatically increase protein suddenly: https://examine.com/nutrition/can-eating-too-much-protein-be...

[st26]

IMO while protein is needed for muscle building, recommendations like 3.3g/kg (I've even seen recommendations of 4.4g/kg) come from a "more is always better" mentality, along with a pop culture obsession with protein.

Personally, a simple flat 100g seems both a reasonable & attainable goal for most regular people building muscle without requiring exceptional diets (here I fall back on naturalism- I cannot believe that exceptional diets are required to get fit). You can easily hit that number with 1/4-1/3lb of meat a day plus whole grains and vegetables.

[lemming]

I don't think it's that, it's more this:

Since higher protein intakes seem to have no negative effects in healthy people, one may want to err toward the higher amounts.

I haven't seen anything over 3.3g/kg recommended anywhere, and most people seem to recommend 1.4-2g/kg as a good baseline amount. The ISSN recommends this (see here: http://stevenlow.org/issn-position-statements-protein-and-ex...), however the ISSN does recommend higher amounts when losing weight:

Higher protein intakes (2.3–3.1 g/kg/d) may be needed to maximize the retention of lean body mass in resistance-trained subjects during hypocaloric periods.

Of course, none of this is required to get fit - you don't need to do the optimal thing to get a basic result. But you'll definitely gain lean mass faster if you do follow this. Those recommendations for weight gain (say 2g/kg with a caloric surplus) is easy to achieve with no supplementation and normal food, at least for an omnivore - vegans may have to work harder to get there.