by Dr. Paul Cribb PhD. CSCS. CISSN. FATES.
Nine times out of ten, whenever someone finds out that I deal with nutrition the next thing out of their mouth is: “How much protein is too much?” or “What happens if I eat too much protein?”
How come no one ever asks: “How much carbohydrate is too much?” or “What happens if I eat too much carbohydrate?”
Personally I think those would be MUCH better questions to ask. Alas, no one does.
So what is the deal with protein....can you have “too much”?
I’ve been researching protein metabolism for 20 years and never been able to find any research, or data at all indicating that there is some amount of intake above which there is damage to an otherwise normally functioning human body.
Photo by Leszek LeszczynskiThe specific issue everyone seems to be worried about is kidney damage. Is there any scientific basis for that concern?
A PubMed search investigating just that question does not reveal any reference to kidney damage from high protein diets in healthy populations. There is some research suggesting that in patients with certain types of Chronic Kidney Disease a low protein diet (protein restricted) can slow the progression of the disease.
Mind you, these studies do not say that high protein intake exacerbates Chronic Kidney Disease. They only suggest that protein restriction guards against the progression of the disease. That is a big and important difference. These studies certainly do not contain any evidence that high protein intake is involved at all in the development of Chronic Kidney Disease in an otherwise healthy person.
The literature is quite clear on this point: “In healthy obese individuals, a low-carbohydrate high-protein weight-loss diet over 2 years was not associated with noticeably harmful effects on GFR, albuminuria, or fluid and electrolyte balance compared with a low-fat diet.” (4)
What we do know is that many factors can affect renal function, among them: high blood pressure and diabetes or insulin resistance. Anything we can do to prevent high blood pressure, diabetes or insulin resistance is only going to help prevent the development of Chronic Kidney Disease. Although it is a topic for a separate discussion, we know that high protein diets can be a crucial part of lifestyle modifications aimed at loosing weight, lowering blood pressure, and preventing diabetes or insulin resistance.
In a nutshell, protein does not cause kidney damage. Higher protein diets can help promote weight loss and can be an important part of lifestyle modifications aimed at lowering blood pressure and preventing diabetes or insulin resistance – all of which are good things both for you and your kidneys. If you have chronic kidney disease a lower protein intake may slow the progression of your disease but that’s it.
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References
1. Pecoits-Filho R. Dietary protein intake and kidney disease in Western diet. Contrib Nephrol. 2007;155:102–112.
2. Lentine K, Wrone EM. New insights into protein intake and progression of renal disease. Curr Opin Nephrol Hypertens. 2004;13:333–336. doi: 10.1097/00041552-200405000-00011.
3. Hiatt R. Ettinger B. Caan B. Quesenberry, Jr C. Duncan D. Citron J. Randomized Controlled Trial of a Low Animal Protein, High Fiber Diet in the Prevention of Recurrent Calcium Oxalate Kidney Stones. American Journal of Epidemiology. Vol. 144, No. 1:25-33
4. Friedman A. Ogden L. Foster G. Klein S. Stein R. Miller B. Hill J. Brill C. Bailer B. Rosenbaum D. Wyatt H. Comparative Effects of Low-Carbohydrate High-Protein Versus Low-Fat Diets on the Kidney. CJASN July 2012 7): (7) 1103-1111