Your concern is very understandable of course.
I've read a few studies on the impact of "high-protein" diets on renal failure, and none confirm any solid findings: "...a causal link between high protein intake and renal function decline cannot be established."
Again, the Zone is NOT a [i:3eff421e8a]high[/i:3eff421e8a] protein diet. Apples and oranges.
But one study fed endurance runners what they called a "high" protein level of 30% of their total calories, (which is what the Zone recommends), and concluded that increasing protein progressed dehydration, and therefore more kidney strain. The author sums it up with:
"In otherwise healthy individuals, a protein intake of no more than 2 grams of protein per kilogram of body weight was recommended by the researchers in order to avoid negative long-term effects." (citation: [url]http://www.akfinc.org/AboutAKF/News.../url])
That maximum recommendation, 2 grams protein per kilo of body weight, exceeds the Zone's maximum of 1 gram per pound of lean body mass.
Eating the Zone's proper protein prescription for your LBM and activity level, balanced with enough carbs and water, should maintain healthy kidney function.