"Increase in kidney size was observed in rats placed on a high protein diet in 1932. The same effect has been noted in numerous other species, including dogs. The number of nephrons is fixed near the time of birth, so the increased size is due to changes within existing nephrons."
Eating like a lion or gorging on animal protein, harms GFR
GFR is the same as kidney functioning. As far as back the 20's we have known that by decreasing protein intake we can increase kidney functioning. Dr. Brenner developed the model for the glomerulus from this ground breaking work. Dr. Walser took this a bit further with small clinical trials, decreasing dietary proteins and supplementing with essential amino acids.