The effect of protein on the kidney is quite a contentious subject because of the many other nutritional factors involved. Additionally the age of a person also affects his kidney efficiency, besides the existing health of the kidney prior to starting protein augmentation.

There is no gradual impact on the kidney workings as the protein is ingested in higher amounts but there is a limit to this ceiling. This is the safe zone that may vary from person to person and therefore paying attention to reasonable protein ingestion is a prudent precaution.

Furthermore, the taking of too much protein does not necessarily help in muscle building as the kidney has a processing threshold (2-3 gm/hr), beyond this which the protein is just filtered in the kidney and expelled in the urine. Too much protein overloads the kidney, requiring it to work harder than necessary to mop up the creatine, albumin, urea & other protein by-products from the bloodstream. Additionally the liver strains in tandem to clear the nitrogen & urea. The intestine can only absorb 1-8 gm of amino acids / hr so spreading protein ingestion over a time period helps.
There are many types of protein and they place different requirements on the kidney. Eg whey protein places less stress on the kidney, milk protein a bit more, and meat protein even more; meaning that the kidney filtration rate has been measured to have increased in instances of different protein consumed. Soy protein is viewed quite favourably in being more gently to the kidneys. Generally, vegetarians have lower blood pressure due to the minimal protein in their diets.

AMERICAN JOURNAL OF KIDNEY DISEASES 'Studies on human subjects (usually without distinguishing the type of protein) indicate that the effects of dietary protein are minimal in nondiabetic patients with no renal injury..'

Diabetes causes kidney damage but if a person is not diabetic, it does not mean that he is exempted from kidney problems. A person without diabetes may also be susceptible to disturbances to the kidney function.

The key is being reasonable in consumption. A larger car may need more litres of engine oil, but overfilling the engine over the recommended level will overload its capability.