Proteins or proteids (from the Greek protos, “primary”) represent a large group of organic compounds formed by sequences of amino acids linked through peptide bonds.
We can imagine amino acids such as building blocks for proteins and peptide bonds such as the glue that holds them together.
Proteins express most of the genetic information: Based on their function, the proteins can be divided into:
- transport proteins,
Proteins are subject to a continuous process of demolition and synthesis – the so-called protein turnover – through which the body is able to continuously renew worn proteins by replacing them with new protein material. In addition, this process allows the body to replace the amino acids used for energy and to deposit new ones to strengthen certain tissues (for example following exercise). The share of amino acids that are degraded daily is on average around 30-40 gm / day.
All the proteins present in our body (about 12-15% of body mass) are in fact functional.
The amino acids involved in protein synthesis are 20 and among these 20 eight are essential [leucine, isoleucine and valine (BCAA), lysine, methionine, threonine, phenylalanine, tryptophan]; during the growth two other amino acids, arginine and histidine become essential.
The term essential indicates the body’s inability to synthesise these amino acids from other amino acids through biochemical transformations. We must therefore introduce these amino acids in the diet.
Food of animal origin has the best amino acid profile because generally they present all the essential amino acids in good quantities. Unlike these, plant-based foods usually have deficiencies in one or more essential amino acids.
However, these deficiencies can be overcome through the right food associations such as PASTA and BEANS. Here we speak of mutual integration because the amino acids with which pasta is lacking are supplied by beans and vice versa.
CALORIES: By burning a gram of protein an average heat of 5.65 Kcal develops. However, since our body cannot use the nitrogen in them, their energy power is reduced to 4.35 Kcal per gram.
Normally 92% of the proteins introduced in the diet are absorbed (97% of the animal ones and 78% of the vegetable ones).
Proteins supply our body on average 4 Kcal per grams.
Role of proteins in the body
- As we have already said, the main function of proteins is to supply the amino acids necessary for tissue renewal processes (plastic function).
- Proteins are also depositories of the genetic code (DNA and RNA of the cell nucleus)
- They act as carriers of various substances present in the blood (haemoglobin, hormones etc.).
- They act as neurotransmitters (serotonin)
- They intervene in blood clotting.
- They are necessary for muscle contraction and for the body’s immune defence.
- They are precursors of enzymes that regulate the speed of reactions and that intervene in the body’s various metabolisms.
- Proteins also have an energetic function in particular conditions, but in a balanced diet this role is marginal. This process is instead active during prolonged fasting when the branched chain amino acids (leucine, isoleucine, valine) are degraded for energy purposes or during prolonged and / or very intense physical activity.
How many proteins in a balanced diet?
Nutritionists recommend taking about 15-20% of the total daily calorie intake of 0.8-1 g of protein per kg of body weight throughout the day.
These proteins should derive 2/3 from products of animal origin and 1/3 from products of vegetable origin.
REMEMBER, the protein requirement is inversely proportional to age:
2 g / kg / day in the newborn, 1.5 g / kg / day at 5 years, 1.2 g / kg / day in adolescent – adult age;
Are all proteins the same?
The amount of protein isn’t the only important parameter; in order for a diet to be considered balanced, we must also consider protein quality.