What determines the need for protein?

The amount of protein used by the body is influenced by various factors. Protein requirements are based on the requirements for essential amino acids. The requirements for the nine essential amino acids established by the WHO are based on nitrogen balance studies. However, this method is questioned by some researchers, who argue that it seriously underestimates the requirements for certain population groups, especially young people and athletes.

Different tissues use amino acids at different rates. During exercise, muscles use branched-chain amino acids, especially leucine.

One study showed that the amount of oxidized leucine determined using nitrogen balance during a two-hour workout at 50% V02max was approximately 90% of the total daily requirement.

Although the presence of oxidized amino acids in muscle reflects increased protein utilization, it does not reflect whole body protein turnover.

Differences in research methods for determining the required amounts of individual amino acids can alter the total protein requirement. But even if the requirements for some amino acids are theoretically higher for physically active people, they are not difficult to obtain from food.

Excess proteins will accumulate as fat, not stimulating intense training.

• Level of exercise. The intensity and duration of exercise increase protein utilization. Resistance and endurance exercise also affect protein utilization. Initiating an endurance program may increase protein requirements for approximately two weeks. Some evidence suggests that leucine oxidation is higher in untrained athletes than in trained athletes, and that with training comes a period of adaptation that may reduce protein requirements.
• Energy and carbohydrate adequacy. If energy supply is inadequate due to diet or increased expenditure, the need for protein increases. It has been established that an increase in the number of kilocalories improves the nitrogen balance. Protein quality. Complete proteins, such as egg white and casein, contain all the essential amino acids, improve protein utilization, and contribute to a minimum amount of nitrogen excreted. Protein in a mixed diet slightly increases the need for it.
• Hormones. During growth (adolescence, pregnancy) the need for protein increases.
• Diseases and physical injuries. Diseases affect protein needs differently in different people, and therefore each person's reaction is individual. Burns, fever, fractures, and surgical injuries cause the body to lose a lot of protein. An athlete may lose 0.3-0.7 kg of protein from the entire body during the recovery period after a limb fracture.