That's not a clear exception at all.
Within some mental model, isolated protein powder is healthy because we generally treat high protein consumption as low-risk for most people and recognize that protein isolates can be very effective for professional and amateur athletes to consume a lot of while building muscle.
In no way does that imply that these protein isolates are "extremely healthy" for the general public or even for anyone in the long term. There's just not any data to say that specifically (it's too niche to perform those kinds of studies), and far too little reason to make that assumption with confidence.
(And it's almost certainly a terrible idea for most people to eat 4-5 chicken breasts per day -- or a comparable amount of protein isolate powder. Please remember that most people are not living a gym bro lifestyle and shouldn't be following gym bro nutritional advice in the first place.)
Protein isn't bad for you and 4-5 chicken breasts is around 120g a day, a healthy amount for an adult. By way of comparison, indigenous people where I live ate hundreds of grams a day in their traditional diets. I've run into this whole "don't eat too much protein, oh man you will die!" nonsense meme before and I wonder where it came from.
> 4-5 chicken breasts is around 120g a day
Bad math? Per USDA standards, a single boneless skinless chicken breast has ~54 grams of protein; so 4-5 would be ~200-250g of protein.
Because that's grossly outside the norm for the general public, you're not going to find any evidence to support the idea it's a healthy amount for a typical person to consume for a long period of time. And likewise, you'll find little evidence saying what negative consequences it might have, if any.
You're welcome to make whatever assumptions you want to in that case, but there's not a lot of ground for anyone to convince skeptics who disagree with them. It's tenuous assumptions all the way down.
Regardless, in the real world, that also represents 1200-1500 calories of absurdly (mind-numbingly) high-satiety food and quite a lot of slow digestive bulk. Most people simply wouldn't be able to consume that while also eating a varied diet that provides them with adequate long-term nutrition. So it's probably a pretty bad idea for them to dedicate themselves to it, unless -- like some athletes and gym bros -- they have the further discipline to also stuff themselves of all the other stuff they need to eat while also not eating so much that they become overweight. Do you know many people like that? I'm not sure I've met more than a handful in my lifetime.
Whatever the impact of the very high protein consumption itself in some abstract theoretical kind of way, which we're far from having evidence into understanding, it's just terrible advice for the general public because of the secondary effects we might reasonably expect in practice.
https://www.thelancet.com/journals/ebiom/article/PIIS2352-39...
> Moreover, epidemiological studies show that a high intake of animal protein, particularly red meat, which contains high levels of methionine and BCAAs, may be related to the promotion of age-related diseases. Therefore, a low animal protein diet, particularly a diet low in red meat, may provide health benefits.
It's possible to die of "protein poisoning" but you really have to be in a survival situation with no sources of fat. Hunters and trappers are known to have died this way when only lean meat was available in far northern winters. Maybe this is where the idea came from.
Consuming high amount of animal protein was pointed out by the urologist as one of the things I should evade. Apparently that contributes to development of kidney stones. So there’s at least one way in which it’s bad for you.