Proteins consist of amino acids
Proteins are found in all body cells and are essentially long chains consisting of 20 different amino acids. 9 of these 20 amino acids are called essential, while the remaining 11 are non-essential. The fact that an amino acid is essential means that the body cannot produce it from other substances available in the body. Therefore, these 9 amino acids must be provided through diet. In turn, the 11 non-essential amino acids can be produced by the body itself. Some of the 20 amino acids are termed conditionally essential, which means they are only required under certain conditions, such as during intensive muscle mass building or in case of illness. Conditionally essential amino acids include arginine, cysteine, glutamine, glycine, proline, and tyrosine.
However, from a nutritional point of view, proteins cannot simply be classified as "proteins", as there are significant nutritional differences between proteins. Proteins with a high content of essential amino acids are called high-quality proteins, and they are proteins with an optimal amino acid composition that meets the body's needs. Animal proteins, i.e., meat, milk, fish, and eggs, are rich in essential amino acids and are almost completely absorbed in the intestines. Thus, animal-based proteins are of high quality, while plant-based proteins are of lower quality. Plant proteins have a slightly less optimal amino acid composition and lower digestibility. This does not mean that, as a vegetarian, you cannot meet your protein needs, but rather that you need to consume the right plant-based protein sources.
Muscles consist of proteins
There are many different proteins in the body and muscles, and when performing strength or endurance training, the body increases the production of certain types of proteins depending on the type of training. Endurance training primarily increases the amount and activity of transport proteins and enzymes, while strength training increases the amount of the structural proteins actin and myosin. Actin and myosin are muscle proteins that ensure muscle contraction. Strength training stimulates protein synthesis, resulting in the production of more structural proteins, i.e., muscle mass increases. After training, the production of muscle proteins increases for up to 48 hours. However, the breakdown of muscle proteins also increases at the same time, though not as much as the formation. Furthermore, the degradation rate also returns to normal more quickly. Thus, muscle growth is the result of a longer period during which the average rate of muscle protein formation has been higher than the rate of muscle protein degradation.
How much protein do you need to consume?
Scientists disagree on this issue, as the scientific community seems to be divided into two groups. On one hand, there are those who believe that physical activity increases protein consumption, and on the other hand, those who believe that athletes' protein consumption is the same as that of the rest of the population. A 2007 review article stated that there seems to be evidence for both claims, so what to believe? However, studies that claimed that protein requirements are not increased were criticized for using too low an intensity, making it unlikely that they could be applied to athletes who train intensely. Furthermore, several studies have shown that strength training athletes have a higher need for protein than the general population.
When researchers want to determine protein requirements, they most often analyze nitrogen balance. All amino acids contain nitrogen, and nitrogen balance is the difference between ingested and excreted nitrogen. Nitrogen is primarily lost in the form of urea in urine, as well as creatinine and uric acid. Smaller amounts are also lost through feces, sweat, and other means. During fasting, there is a negative nitrogen balance, while during growth, it is positive; if a person is in nitrogen balance, the amount of nitrogen consumed, of course, matches the loss. Body proteins are continuously broken down and formed, and protein turnover is much higher than intake, meaning the body recycles a large portion of the amino acids from broken-down proteins.
In an average energy balance, the required amount of protein is the minimum amount that compensates for daily nitrogen loss. Based on nitrogen balance studies, the WHO has determined that the average daily protein requirement for an adult is 0.75 grams of high-quality protein per kilogram of body weight. Therefore, the nitrogen balance method is used to estimate how much protein is needed to avoid a deficiency. However, this method is subject to several uncertainties and is not particularly suitable for determining the optimal protein intake for trained individuals.
Several studies conducted in the late 80s and early 90s showed that official protein recommendations do not cover the needs of strength training. The increased need is also useful because minor muscle damage is repaired after training and muscles can grow.
Sports physiology and nutrition textbooks indicate that strength athletes need approximately 1.4-1.8 grams per kilogram of body weight and that additional protein consumption provides no additional benefit. Furthermore, protein needs are usually met with a diet conducive to hypertrophy, as it provides plenty of calories and, if the diet is sufficiently healthy and varied, also plenty of protein.
