By Dr. Davide Marciano
Protein quality and Amino acids
Proteins are the building blocks of our body, useful for repair, maintenance and muscle growth, sacrificed for energy purposes when nutrition is inadequate.
In such cases, in order to satisfy one's metabolic needs, the body catabolizes its muscle tissue.
During digestion, proteins are broken down into simpler units called amino acids, which are the basic components from which the protein originated.
Proteins come in various sizes and shapes, divided into two categories:
SIMPLE PROTEINS, consisting only of amino acids
a) Serum albumin, present in the blood
b) Lactobumin, present in milk
c) Ovoalbumin, present in eggs
d) Myosin, present in the muscles
e) Collagen, present in the connective tissue
f) Keratin, present in hair, hair and nails
CONJUGATE PROTEINS, composed of amino acids and non-protein molecules.
a) Nucleic Acids, present in the chromosomes
b) Phosphoproteins, present in casein.
The body needs 22 amino acids to synthesize a protein. Thirteen of these can be produced by the body, while the other nine must be taken through the diet.
The former are called NON ESSENTIAL AMINO ACIDS, while the latter are ESSENTIAL AMINO ACIDS.
The proteins that contain all the essential amino acids are called COMPLETE, while the proteins that lack one or more essential amino acids are called INCOMPLETE.
All dairy products, meat and fish are complete foods. All starches (except soybeans), vegetables, fruit are incomplete.
The proteins provide 4.0 calories per gram.
The amount of protein that the body can use is called BIOLOGICAL VALUE.
The body is not able to store proteins, as happens with carbohydrates, so they are continuously broken down and recomposed. This process must be continuously fed by the proteins contained in the food.
In muscle training, the BRANCHED AMINO ACID also called BCAAs (leucine, isoleucine and valine) are metabolized.
The sportsman needs about 1.4-2 g of protein per kg of body weight, which in the case of the bodybuilder, especially in the definition periods, can even reach 2.5 - 3g.
Excess protein is also converted into body fat.
A high-protein diet involves blood acidosis, work overload for the kidneys and liver and digestive difficulties.
Digestion of the proteins
In the stomach, proteins are broken down into their components (amino acids) by some enzymes that break the bonds between the amino acids themselves. Less than 5% of the ingested protein is then lost in the faeces.
The amino acids are then absorbed by the intestinal villi, thanks to several CONVEYORS. Many of them carry more than one amino acid. This explains the mistake of many people who take excessive amounts of a single amino acid: this error leads to an excessive work of a given transporter, thus damaging the transport of the other amino acids that use it.
