Strength Training and Protein
According to the latest studies strength training increases the daily protein metabolism by 17% on constant muscle mass.
The physiological limit of muscle mass composition is around 5kg/ year. This would mean a weight gain of 1kg body protein a year as muscles are comprised of 20% protein. This means that an additional amount of 2.8 g of protein has to be consumed daily.
The DGE (Deutsche Gesellschaft für Ernährung - German Nutrition Society) recommends a protein intake of 59g/day for men aged between 19 and 51 which means:
59 g recommended intake of protein
+ 17 % for physical work out
+ 2,8 g for muscle growth
= 71,8 g/day protein demand
If you take into consideration that the average German consumes a lot more protein than recommended by the DGE, it becomes clear that body builders do not need protein supplements or amino acid mixtures.
Endurance Sport and Protein
The protein demand can be increased up to one and a half times more than the normal amount required which is dependant on the amount and intensity of the exercise. The cause of this is gluconeogenesis from body protein. Glucose is bio-synthesised (made by) out of non-carbohydrate sources (amino acids) as a result of a glucose deficiency brought about by the physical exercise. Up to 20g body protein can be decomposed in a marathon for example. This high amount is proportional to the energy used during the exercise (as it is with those who do strength training). If as recommended by DGE 12 - 15% of the daily energy input is consumed in the form of protein the additional protein needs will be covered during the replacement of consumed energy, i.e. through additional consumption of foods. So even in this case it is not necessary to add more protein to the diet.
In case you still decide to take protein or amino acid supplements, please note the following:
A constant excessive intake of protein can be harmful to the kidneys and metabolism and will eventually lead to illnesses.
If more proteins are being consumed than necessary, it is recommended to drink more fluids as the energetic use of excess protein in the liver leads to the development of uric acid. The kidneys need water in order to excrete uric acid.
Sports Nutrition for Endurance Athletes, 3rd Ed., Monique Ryan
The Protein Power Lifeplan
The High-Protein Cookbook : More than 150 healthy and irresistibly good low-carb dishes that can be on the table in thirty minutes or less.