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Too much protein isn't good for you, infact it's terrible for you as your kidney gets f*cked over trying to get rid of all the extra protein
So what are the medical facts behind these claims and why do so many people, including some medical professionals and nutritionists, still believe it?
For starters, the negative health claims of the high protein diet on kidney function is based on information gathered from people who have preexisting kidney problems.
Any studies that show a correlation between renal (kidney) dysfunction and protein intake are in those with some type of diagnosed, pre-existing renal (kidney) disease like diabetic nephropathy, glomerular lesions, etc. Even research into protein restriction for renal patients can be controversial. (Shils, Modern Nutr in Health & Dis, 1999).
Besides, you’ll likely recognize a serious pre-existing kidney condition; the signs and symptoms will clue you in long before you happen upon it with a routine blood test (especially if there's a noted family history of diabetes mellitus and hypertension).
You see one of the jobs of the kidneys is the excretion of urea (generally a non toxic compound) that is formed from ammonia (a very toxic compound) which comes from the protein in our diets. People with serious kidney problems have trouble excreting the urea placing more stress on the kidneys and so the logic goes that a high protein diet must be hard on the kidneys for healthy athletes also.
Now for the medical and scientific facts. There is not a single scientific study published in a reputable peer - reviewed journal using healthy adults with normal kidney function that has shown any kidney dysfunction what so ever from a high protein diet. There aren’t even any correlational studies showing this effect in healthy people.
Not one of the studies done with healthy individual I have read, has shown any kidney abnormalities at all. If you happen to know even only 1 study, please let me know.
Furthermore, animals studies done using high protein diets also fail to show any kidney dysfunction in healthy animals. Now don't forget, in the real world, where millions of athletes have been following high protein diets for decades, there has never been a case of kidney failure in a healthy athlete that was determined to have been caused solely by a high protein diet.
If the high protein diet was indeed putting undo stress on our kidneys, we would have seen many cases of kidney abnormalities, but we don't nor will we. From a personal perspective as a consultant for many top bodybuilders in my country, I have known bodybuilders eating high protein diets (300 – 400 grams a day) who showed no kidney dysfunction or kidney problems and I personally read the damn blood tests!
Bottom line? 1-1.5 grams or protein per pound of bodyweight will have absolutely no ill effects on the kidney function of a healthy athlete, period. Now of course too much of anything can be harmful and I suppose it's possible a healthy person could eat enough protein over a long enough period of time to effect kidney function, but it is very unlikely and has yet to be shown in the scientific literature in healthy athletes.
Since an exhaustive search of the published literature will likely not yield a single study showing that the amount of protein in the diet causes, or is correlated with, the onset of renal dysfunction in otherwise healthy individuals, the fact that this notion prevails is puzzling to say the least!
But even if a doctor were to find an obscure reference that might suggest a relationship between a high-protein diet and kidney disease, there are numerous studies showing otherwise. Here are a few of them:
a) Ann Intern Med 2003 Mar 18;138(6):460-7
The impact of protein intake on renal function decline in women with normal renal function or mild renal insufficiency.
Knight EL, Stampfer MJ, Hankinson SE, Spiegelman D, Curhan GC.
b) 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.
c) 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.
d) 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.
e) 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."