Le protein they are polymers composed of amino acids (aa - monomers) bound by peptide and hydrogen bonds; from a chemical point of view, aa are quaternary molecules (basically composed of: carbon - C, hydrogen - H, oxygen - O and nitrogen - N) which, by structuring thousands of biologically different proteins, are indispensable for the survival of the human organism.
There are 20 L-amino acids, or ordinary amino acids: alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine and valine; from their metabolism it is possible to obtain more than 500 molecules, but almost all of them can be synthesized by the human organism. The only ones that need introduction with the diet are said to be essential and for the adult they are: phenylalanine, leucine, isoleucine, lysine, methionine, threonine, tryptophan and valine, while for the child they are 2 more, respectively: histidine and arginine .
More information on proteins
Proteins perform numerous functions; among the most important are: structural, bioregulatory, immune, transport, cell membrane channel, energetic, hormonal, neurotransmission, etc.
Dietary protein intake therefore has the function of complying with all the biological needs of the organism, which differ mainly in terms of: age, sex, physical activity, body structure and muscle mass, special pathological or physiological conditions.
An adult, healthy and sedentary organism can survive with 0,75 grams (g) per kilogram (kg) of weight (physiological, not overweight or underweight), while a growing subject needs about 1,5 g / kg.
Sportsmen, athletes, pregnant and sick women need a more detailed estimate than that obtainable through the tables referring to the general population.
In the nutritional field it is common to hear about "lean proteins"; in reality, it is an improperly attributed denomination which, rather, refers to predominantly protein foods with low fat content.
Which ones are they
Lean proteins are mainly associated with lean meats from burrows (rabbit) or poultry (mainly chicken and turkey). Lean proteins of veal (young bovine), horses, some fishery products (molluscs, crustaceans and fish), egg white and skimmed yogurt are also frequently consumed.
On the contrary, legumes associated with cereals are less used (a technique useful for improving their biological value) and lean proteins deriving from game, frogs, land snails and ostrich muscle are almost totally ignored.
"Lean Protein" Table (values per 100g of edible portion)
|Guinea fowl breast||25.8||1.9||32.0|
|Egg - Albumen||10.7||Tracks||0.0|
As can be seen from the above values, almost all lean proteins have a very low cholesterol intake, with the exception of some molluscs and some crustaceans (in the red table).
The following were deliberately excluded: tofu, soy milk and low-fat cottage cheese, as the lipid profile differs too much from that of meat foods, and for the same reason it was decided NOT to include legumes due to the excessive importance of carbohydrate profile; legumes, especially if associated with cereals, boast a good protein content and quality ... but these are in any case not comparable to those of lean meat, fishery products and egg white.