Damage to kidneys is a side effect of excessive protein it is a well researched and absolute phenomenon. However, mild ammonia saturation is not damaging if it's just on the threshold, and it varies on the size of the person, and on what the rest of their diet is like.
Toxicity happens when your body loses the ability to convert ammonia to urea and becomes saturated. As such the nitrogen from every extra g of protein stays in the body as as ammonia, which is toxic or a toxin to the body.
Apparently toxicity start around 160-200g a day of protein consumption. However I'm looking more into this, and how much body size/lean body mass/and so on affects this.
Obviously it's also about maintaining a good nitrogen balance in the body (nitrogen balance is dietary protein = metabolised protein basically). However it's going to vary - as I said, there are so many factors to take into consideration, some people are going to need x amount of g per kg, and others are going to need xx g per kilo - that's why I've always hated those generic "use x amount of protein per kg of body weight" as it's so variable. Also it depends if you're on a calorie deficit or not, if so you'll need more protein for balance (if you don't want to lose muscle mass) and less if not on a deficit.
Excess protein consumption isn't a lol-worthy comment - but it's also not as ridiculous as they state in that article.
I wonder whether upping leucine would help decrease the risk as it improves protein synthesis?? That should lower your nitrogen balance right? As from my research it would seem that a protein intake above 25% of what is need to get a nitrogen balance of zero would have no effect on muscle gain...
Oh this is all so complicated.
Eitherway, it's never been an issue for most of us as none of us are stupid enough to take anywhere near that much protein anyway.