I have to say, I know that the mix I make is high in protein, but not enough to cause issues. And it is certainly not for everyone. But I do have healthy hens, and over the years I have not lost any to protein level fatality. Indeed, they all live long happy lives and die of age related issues. As you can see, I treat them as pets with dividends (eggs), and none go into a pot (those come from a local butcher or Purdue).
Admittedly, my feed mixture has fluctuated over the years, but I always strive for high protein and variety in their diet. For instance, even though they all free range during the day, I add a cup of dried mealworms in their feed during the winter months, and whenever they are molting as well.