Protein is macro nutrient, which is treated with special care in the fitness and bodybuilding world. There exists a conviction, according to which, one of the key factors limiting the tempo of development of muscle tissue is insufficient consumption of proteins. The same way high-protein diet is treated as a remedy possible to block muscle catabolism, of which the risk rises during body fat reduction. As a result, many people provide more protein than it is necessary. It's good to think what is the level over which the supply of protein becomes potentially dangerous.

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Protein and kidneys: facts and myths

The biological role of protein

Protein is indispensable macro nutrient of our diet, consisting of elementary particles – amino acids connected with one another with peptide bond. From biological point of view, amino acids are used in the process of body's protein synthesis (those proteins create, e.g. muscle tissue, but also enzymes and some hormones). Dietary proteins vary when it comes to structure and the content of some amino acids, which is noticeable in their nutrition value.

The demand for proteins

It's not so easy to set the optimal daily intake of proteins. However, on the basis of observations and experiments, it was possible to set the recommended range of supply of this macro nutrient. The minimal daily consumption of protein by an adult is at least 0.65g per 1 kg of body mass. A dose recommended for people doing moderate physical activity ranges between 0.8 to 1.0g / 1 kg of body mass per day. In case of physically active people, especially sportsmen, the suggested intake of protein ranges from 1.2 to 2g per 1 kg of body mass, whereas, the upper limit concerns the competitors of strength and speed disciplines. In case of endurance sportsmen there is usually no need to cross the limit of 1.4 g per 1 kg of body mass per day.

An additional factor, which increases the demand for proteins may be calorific deficit in diet – in this case the recommended intake may range between 2.3 – 3.1 g per 1 kg of lean body mass per day. Nowadays many people eat more protein than that. It mainly concerns bodybuilders and amateurs at the gym. The reason for such behaviour is the conviction that higher intake of protein from diet causes faster development of muscle tissue and better results in body fat reduction. And so, some competitors consume 3 to 5 g of protein per 1 kg of body mass per day, or even more. In case of such doses, there are doubts if they are necessary and safe for health...

Safe limit of protein intake according to research

The maximal daily dose tolerated by human body depends on few factors, and the main ones are following:

  • the efficiency of digesting proteins and the tempo of absorbing amino acids from digestive tract,

  • the efficiency of the process of neutralising the toxic ammonia to urine in the liver,

  • the ability of removing metabolites of amino acid transfer by kidneys with urine.

All of those factors matter, whereas, the most important for people without kidneys disorders is the second one.

Studies done by Rudman et. al in 1973 showed that the maximal tempo of sythesis of urine from ammonia is 65 mg/hour, which gives about 325g of proteins per day. This amount was counted for a man weighing 80kg, and it gives about 4.1 g per 1 kg of body mass. It is definitely high limit in comparison to the present recommendations concerning the intake of proteins by sportsmen. However, that amount is sometimes exceeded by particular competitors or even amateurs training for their own satisfaction. You should remember that such behaviour connected with nutrition is potentially dangerous. There are also recommendations stating that the amount of energy from proteins should not be higher than 35% of the calorific content of diet.


As long as the optimal intake of proteins for physically active people is rather lower than 2g per 1kg of body mass (or 3.1g per 1kg of lean body mass during energetic deficit state), the maximal safe intake of that macro nutrient is about 4.1g per 1kg of body mass. You should not exceed that amount, because it may damage your health.