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Protein and Kidney Function

By Dr. John M Berardi, Ph.D.
First published at www.skifaster.net, 2001.

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The effects of a high protein diet have been debated for years. Although studies have been published showing that in individuals with unhealthy kidneys, an excessive protein intake could place undue strain on their kidneys, there is no good data to suggest that healthy individuals anything to worry about with high protein diets. A recent study was conducted to investigate this very question. In this study, two groups of athletes were examined to determine the potential renal consequences of a high protein intake. Group one consisted of body builders and group two consisted of other highly trained athletes (cyclists, rowers, martial artists). Both blood and urinary analyses were conducted during rest and during exercise.

On average, the body builders consumed about 3,900 calories and 169g of protein per day (1.94g/kg) while the other group consumed 2,600 calories and 99g of protein per day (1.35g/kg). Some of the bodybuilders consumed a protein intake of up to 2.8g/kg.

Nitrogen balance (a measure of the amount of protein eaten minus the amount excreted) was positive in all athletes eating more than 1.26g of protein/kg but no different between groups.

Although some blood parameters (blood uric acid and calcium) were higher in the body builders, there was no correlation between protein intake and markers of kidney function (creatinine clearance, albumin excretion rate, and calcium excretion rate).

The researchers concluded that protein intake under 2.8g/kg does not impair renal function. From the results of this study, there is finally evidence that high protein diets may not be harmful to the kidneys of healthy athletes. It appears that high protein diets are only harmful in those who have pre-existing kidney dysfunctions. Prior speculations that high protein intake would cause kidney damage appear unfounded.

Poortmans, JR and Dellalieux, O. Do regular high protein diets have potential health risks on kidney function in athletes? Int J Sport Nutr Exerc Metab. 10(1), 28-38, 2000.