Le protein o protidi (from the Greek protos, "primary") represent a large group of organic compounds formed by sequences of amino acids linked together through peptide bonds.
We can imagine amino acids as i bricks for the construction of proteins and peptide bonds such as the glue that holds them together.
Proteins express most of thegenetic information; based on their function they can be divided into: enzymes, transport, contractile, structural, defense and regulatory proteins.
Proteins are subject to a continuous process of demolition e synthesis - the so-called turnover protein - through which the body is able to continuously renew worn out proteins by replacing them with new protein material.
Furthermore, this process allows the body to replace amino acids used for energy and deposit possibly new ones to strengthen certain tissues (for example following physical exercise). The amount of amino acids that are degraded every day averages around 30-40 g / the.
This is called protein share di wear and tear and it must be introduced daily with the diet because our body does not have protein reserves; all the proteins present in our body (about 12-15% area of body mass) are indeed functional.
Essential amino acids
- fundamental amino acids involved in protein synthesis are 20 and among these 9 I am totally essential (AAE) - leucine, isoleucine and valine (BCAA), lysine, methionine, threonine, phenylalanine, tryptophan, histidine - during growth or in conditions of "homeostatic precariousness" (for example, pathologies) others 3 amino acids, thearginine cysteine and tyrosine become essential (normally defined conditionally or limitedly essential). The term essential indicates the body's inability to synthesize these amino acids from other amino acids through biochemical transformations. These amino acids must therefore be introduced with the diet. Foods of animal origin have the best amino acid profile because they generally have all the essential amino acids in good quantities. Unlike these, foods of plant origin usually have deficiencies in one or more essential amino acids. However, these deficiencies can be overcome through correct food alternations, for example cereals and legumes - it was once believed that it was necessary to combine them in the same meal; today we know that it is enough to alternate them regularly. In this case we speak of mutual integration because the amino acids that pasta is lacking are supplied by the beans and vice versa.
How many Calories
Oxidizing one gram of protein develops an average heat of 5,65 kcal. However, since our organism is unable to use the nitrogen contained in them, their energy power does decreases a 4,35 kcal per gram.
Normally it comes absorbed il 92 % of the proteins introduced in the diet (il 97 % of those animals and the 78 % of vegetable ones). It follows the proteins provide to our body on average 4 kcal / g.
At the gastric level (stomach) proteins undergo a partial degradation thanks to the action of the gastric juice and hydrochloric acid, which will come completed in the first part of the small intestine (duodenum).
To optimize the digestion el 'absorption protein is good:
- avoid associating protein foods of different origin (eggs and cheeses, or milk and meat);
- avoid associating protein with a meal ricco di carbohydrates (a small amount, such as a piece of bread is obviously tolerated);
- combine small doses of acidic foods such as lemon juice or vinegar;
- combine a little vegetable with the protein meal which, in addition to avoiding intestinal putrefaction phenomena, thanks to the high intake of vitamins and minerals, favors the enzymatic action;
Functions and Biological Role
- As we have already said the main function of proteins is that of supply the body of fundamental amino acids necessary for the processes of renewal tissue (plastic function);
- Proteins are likewise depositary of genetic code (DNA and RNA of the cell nucleus)
- They act as transporters (carrier) of various substances present in the blood (hemoglobin, hormones, etc.);
- They act as neurotransmitters and they are the basis of many hormones (e.g. serotonin and insulin);
- Speakers in the coagulation of blood;
- They are necessary for the muscle contraction;
- They are indispensable for the immune defense;
- They are precursors of enzymes (biological catalysts) which regulate the speed of reactions and which intervene in the various metabolisms of the body;
- Proteins also have a function in particular conditions energy, but in a balanced diet this role is secondary. This process is instead active during the prolonged fasting or during a lot of physical activity prolonged, mostly intense - when the branched-chain amino acids (leucine, isoleucine, valine) are degraded for energy purposes directly by the muscle and the circulating ones are converted by the liver by neoglucogenesis.
Functions of proteins
How Much Protein
How Much Protein in a Balanced Diet?
Nutritionists advise adults sedentary to consume an amount of protein equal to 0,8 1,2 g of protein for kg di body weight physiological. In adolescence, 1,5 g / kg is essential. Pregnant women require little more than normal. For the strength athletes, this recommendation can reach the doppio - while endurance athletes have a need close to (or slightly higher) than the maximum limit for ordinary people. There are special cases, such as chronic malabsorption in old age, in which it may be necessary to increase the normal dose. In other circumstances, such as some forms of renal and hepatic impairment, the diet must instead be less protein than usual.
It could be said that the absolute protein requirement is inversely proportional to age, while the relative one follows the opposite trend: 2,0 g / kg / day in the newborn, 1,5 g / kg / day at 5 years, 1,2, XNUMX g / kg / day in adolescence - adulthood;
The amount of protein DON'T it is the only important parameter; in order for a diet to be considered balanced, it is also necessary to consider the quality protein.
These proteins should derive for i 2/3 from products of animal origin and for 1/3 from products of origin vegetable. This ensures sufficient biological value - and thus all AAEs in the right proportions and quantities.
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