Here's ya go then bud, 'proof' high protein intake does
not affect kidneys (we know it's needed for muscle repair so it's obvious that the more you damage the muscle the more protein it takes to repair it and build it stronger!):
Int J Sport Nutr Exerc Metab 2000 Mar;10(1):28-38
Do regular high protein diets have potential health risks on kidney function in athletes?
Poortmans JR, Dellalieux O.
Int J Obes Relat Metab Disord 1999 Nov;23(11):1170-7
Changes in renal function during weight loss induced by high vs low-protein low-fat diets in overweight subjects.
Skov AR, Toubro S, Bulow J, Krabbe K, Parving HH, Astrup A.
Am J Kidney Dis 2003 Mar;41(3):580-7
Association of dietary protein intake and microalbuminuria in healthy adults: Third National Health and Nutrition Examination Survey. "Dietary protein intake was not associated with microalbuminuria in normotensive or nondiabetic persons."
If you're interested, these studies can be accessed at
www.pubmed.com.
Some studies in healthy individuals do show an alteration of kidney function with very high protein diets. However, it's important to note that these changes are not reported as negative or "adverse." Instead, they seem to be structural adaptations to increased filtration (something the kidneys are doing all the time anyway).
If the kidney didn't respond this way, most clinicians would think something was wrong. Just like in weight training, tissues adapt to the demands put on them. Therefore, just because the kidneys have to "work" harder, doesn't mean that this is a negative thing.
After all, what happens when muscles work harder? Well, they adapt to the demands and become bigger, stronger, or more efficient. Therefore, the adaptation that kidneys undergo is reasonable and appropriate.
But don't take my word for it, check out this study (again at
www.pubmed.com):
Eur J Clin Nutr 1996 Nov;50(11):734-40
Effect of chronic dietary protein intake on the renal function in healthy subjects.
Brandle E, Sieberth HG, Hautmann RE.