Protein and kidneys: facts and myths

Adequate protein intake satisfying the daily requirement is an important part of a healthy diet, it is absolutely essential for the proper functioning of the human body. It is assumed, depending on the source, that in the case of adults with average physical activity the demand for protein is within the range of 0.8-1.1 g per kg of body weight (with normal BMI).

Active people, though, especially enthusiasts of strength trainings and endurance athletes, require more protein to cover their increased demand. Since precise determination of the needs of an athlete's organism is hard, and in general the role of protein as a diet component is overrated, not uncommon are recommendations to take 2.5 g of protein per kg of body weight. And in some cases even more.

Let's picture it this way: for an 85-kilogramme athlete 2.5 g of protein per kg of body weight is 212 g of protein per day. It makes over a kilogramme of lean meat or 35 medium-size eggs. In recent years, a number of high-protein diet followers increased owing to the slimming protein diet of Dr. Pierre Ducan. Paradoxically, the high supply of protein used in the diets focused on the growth of muscle mass can also be used for the reduction of body fat.

In this article I will not consider dietary recommendations or practices, however, I would like to take security into consideration. Much is said about the high protein intake's negative effects on health, especially on renal functions. In fact, the metabolism of amino acids making up the protein leads to the formation of toxic ammonia, which must be neutralized to urea and excreted by the kidneys. But can consumption of high doses of protein actually damage your kidneys?

It was the scientists of the Free University of Brussels who decided to answer this questions by conducting a study in bodybuilders and athletes in other disciplines using high-protein diets. For this purpose, the group of respondents went on a seven-day diet providing 2.8 g protein per kg of body weight. Blood and urine samples were taken to determine the impact of such a model of nutrition on the basic functions of kidneys and other physiological parameters. Both creatinine clearance (excretion of a substance which allows to estimate the state of health of the kidney), urinary albumin and calcium excretion was in the normal range and was not significantly correlated with the amount of supplied protein, which coincides with other studies that verified this dependence.

This means that high-protein diets involving the intake of protein (in this case) in the amount of 2.8 g per kg of body weight do not pose a direct threat to the health and do not impair renal functions. It does not mean, however, that you can freely gorge on protein, but only that popular beliefs on the impact of this nutrient on health are overly demonised.