Proteins as basic building blocks of life. The scientific term protein means as much as “the first” or “the most important”. Proteins perform a variety of functions in the human body. They are building blocks of tissue (e.g. tendons, skin, muscles). In addition, proteins form almost all enzymes and some hormones. The antibodies of the immune system also consist to a large extent of proteins. In addition, proteins also serve as transport proteins for fats (lipoproteins) or for oxygen (haemoglobin).
Amino acids – building blocks of proteins
Proteins and peptides are composed of amino acids. Most proteins consist of a limited number of up to 20 different amino acids. Some amino acids must be ingested with food (essential amino acids), while the body can synthesize some itself (non-essential amino acids).
Semi-essential amino acids
A third form of amino acids are the conditionally dispensable or semi-essential amino acids. Under certain conditions, the body is not able to synthesize these amino acids, or cannot synthesize them sufficiently (e.g. during growth phases or metabolic stress). Semi-essential amino acids include:
- Arginine (newborns, severe diseases)
- Cysteine (newborns, liver diseases)
- Histidine (newborns, chronic kidney diseases)
- Tyrosine (newborns, phenylketonuria)
- Serine (for disturbed kidney function)
Which foods provide proteins?
There is vegetable and animal protein. Animal protein is usually the most valuable source of protein; the body can use them to produce its own protein more efficiently.
Typical Animal Protein Sources
- dairy products
Typical vegetable protein sources
Evaluate the quality of protein
Foods differ in their amino acid composition. Since the amino acid profile of dietary proteins is never identical to the amino acid profile of body proteins, they are said to have a “lower quality”. The amount of amino acids contained in the dietary protein does not limit protein synthesis. The limiting factor is the concentration of the amino acid that has the greatest deficit in terms of demand. This is called the limiting amino acid.
When a limiting amino acid is depleted, the body cannot produce any more proteins. It is then missing, similar to a puzzle, the appropriate building block. Basically, we do not have a protein requirement, but an amino acid requirement.
Proteins and amino acids are not only building materials.
Carbohydrates and fats are preferred in energy metabolism. Amino acids are only increasingly oxidised during prolonged stress, during hunger metabolism or when there is a large protein supply from food. In the hunger metabolism (in catabolic phases), the body uses proteins from muscle tissue as an energy reserve. Excess protein is not used to build muscle, but as a source of energy.
Therefore, a balanced energy balance should always be achieved. It is virtually impossible to build up “mass” while the body is starving.
After training, the body is in an “anabolic time window” for about 3 hours. In this phase the body can rebuild and regenerate new structures particularly well. In this phase carbohydrates and proteins should be supplied. Through the availability of amino acids and the simultaneously stimulated insulin secretion by the carbohydrates, the muscle protein synthesis should be stimulated to the maximum.
45-75 g carbohydrates and approx. 15-25 g proteins are recommended. A side effect is that the glycogen stores are replenished more quickly.
The protein requirement of the organism is ultimately dependent on various factors such as higher energy requirements or structural stress (athletes or non-athletes), special circumstances (such as illness, injury or pregnancy) or growth phases (children, adolescents, strength athletes). The increased protein requirement can at best be covered by a balanced diet. Otherwise, it is possible to cover the increased protein requirement with protein supplements.
Protein requirement of athletes
According to the literature, there are sometimes very different recommendations for athletes. For endurance athletes the recommendations for protein are about 1.2 – 1.4 g/kg body weight and for strength athletes 1.6 – 1.7 g/kg body weight. Some sources recommend even higher values.