Proteins are considered as the "bricks" of the body. They form the basis of all living cells. Protein is an essential nutrient for life.
Proteins are large molecules made up of a specific combination of amino acids.
There are some which our body uses. They are provided either by food or by other ingested amino acids. The body does not have a supply of amino acids, so it has a constant need for them. If there is a lack of amino acids, the body and muscles will draw on the reserves in order to maintain the vital functions.
There are 20 amino acids divided into 2 groups:
- Essential amino acids which are necessary for life. Our body does not know how to synthesise these, they must be provided through food. This is the most important group for muscle function.
- Non essential amino acids form the second group. They can be produced by our body.
The body doesn't know how to synthesise essential amino acids. This means that the body needs a balanced daily ration of proteins containing all the essential amino acids in an appropriate quantity.
In this respect, animal proteins are far more interesting than vegetable proteins. In fact, animal proteins contain all essential amino acids, unlike vegetable proteins.
In order to reflect the balance of amino acids in food, a classification has been established. It is the "biological value" of the proteins. The reference value is the value of the egg with a value equal to 100. Meat and fish have among the highest values (between 80 and 90) and vegetables have some of the lowest values (between 50 and 75).
Proteins: Difference in quality
The quality of the proteins ingested per day is far more important than the quantity. Proteins are not all equal in terms of quality. This is characterised by their essential amino acid content and their digestibility. We know that animal proteins are "superior" in terms of quality as compared with vegetable proteins, due to their composition of essential amino acids. Once there is a lack of amino acids, the body's use of other amino acids will be limited in proportion to the shortfall.
The amino acids which form proteins have 3 major roles:
Proteins play a structural role
Proteins can be made up of between 10 and 2000 amino acids. There is therefore a multitude of proteins with varied functions: Muscle fibres, bone structure, the structure of our skin, hormone receptors, antibodies, enzymes... The structure of a protein is so specific that a small modification can alter its functions.
Proteins play a functional role
Amino acids are the precursors of many important molecules (hormones, neuromediators). Some amino acids are also capable of stimulating protein synthesis, particularly in the muscles. Some amino acids are also involved in the immune system.
Proteins play an energy role
Amino acids provide 4kcal/g. During endurance sport they are only used as a source of calories in the event of a lack of glycogen. A sufficient supply of carbohydrates during prolonged exercise avoids the use of proteins as energy fuel.