The amount of protein used by the body is affected by various factors. The protein requirement is based on the need for essential amino acids. The requirements for nine essential amino acids, established by WHO, are based on the study of nitrogen balance. However, this method raises doubts among some researchers who claim that it seriously underestimates the needs for certain groups of the population, especially such as youth and athletes.
Different tissues use amino acids at different rates. During muscle loading, amino acids with a branched side chain, especially leucine, are used.
One study showed that the amount of oxidized leucine, determined with a nitrogen balance, for a two-hour load and 50% of V02max was approximately 90% of the total daily requirement in it.
Although the presence of oxidized amino acids in the muscle reflects increased protein utilization, this does not evaluate the exchange of protein throughout the body.
Differences in research methods for determining the required amounts of individual amino acids can change the required amount of the whole protein. But even if the demand for some amino acids is theoretically higher for physically active people, getting them from food is not difficult.
Excess proteins will accumulate in the form of fat, without stimulating enhanced training.
- Load level. The intensity and duration of the load increase the utilization of proteins. Exercises for resistance and endurance also affect the utilization of proteins. Initiation of the endurance program can increase the need for protein for about two weeks. Some evidence suggests that leucine oxidation is higher in untrained athletes than in trained athletes, and with training a period of adaptation is coming, possibly reducing the need for proteins.
- Adequacy of energy and carbohydrates. If the energy supply is inadequate due to a diet or increased costs, then the need for protein increases. It is established that an increase in the number of kilocalories improves the nitrogen balance. The quality of proteins. High-grade proteins, such as egg protein and casein, contain all essential amino acids, improve the utilization of protein and contribute to the minimum amount of nitrogen released. The protein in a mixed diet slightly increases the need for it.
- Hormones. In the period of growth (adolescence, pregnancy), the requirements for protein increase.
- Diseases and injuries. Disease varies in different ways in the need for protein in different people, and accordingly the reaction of each individual. Due to burns, fever, fractures and surgical trauma, the body loses a lot of protein. The athlete in the recovery period after fracture of the limb can lose 0.3-0.7 kg of the protein of the whole organism.