Proteins

Proteins are essential nutrients in athletes’ nutrition. They have numerous important functions in organism, that significantly influent on physical abilities.

Proteins have complex chemical structure, and they are contained of carb, oxygen, hydrogen and nitrogen. These four elements enter the composition of all amino acids that build proteins.

Twenty amino-acids in the body of human enters the protein building that are part of various tissues, hormones, enzymes, neurotransmitters and other important substances.

Each amino-acid has amino(NH₂) and carboxile(COOH) group, that give puffer properties to acids, which structure are they a part of.

Amino-acids are mutually connected in proteine molecule with PEPTID CONNECTIONS. Combinations of amino-acids in proteine molecules can be various, what is important for numerous functions of protein in organism. Number of amino-acids in proteins can be over 300(highmolecular polypeptides).

All of the amino-acids can be shared into essential and non-essential. Essential amino-acids can’t be synthetized in organism, so they have to be taken daily by food. From 20 amino-acids, 8 are essential. In childhood essential acids are also histidine and arginine, because they are not synthetized quick enough, or in amount that is necessary for intensive processes of growth in this part of life.

Essential amino-acids have to be present at the same time in organism to synthetize necessary proteins in different tissues. In reversed case synthesis will be stopped, and present amino-acids will be degradated and used on the other way.

Essential and non-essenital amino-acids

Essential: histidine, fenilalanine, isoleucine, lysine, methionine, treonine, tryptophan, valine, leucine

Non-essential: alanine, cysteine, glycine, arginine, asparagine, cystine, proline, serine, aspartat acid, glutamine acid, glutamine, tyrozine

Groceries that enable protein intake

Proteins that are present in animal food contain all essential amino-acids in proportions that are the most favorable for usage in digestive tract, liver and other tissues, so they are often called high-quality proteins.

Plant proteins often don’t contain all essential amino-acids; most often three amino-acids have lower concentration: lysine, tryptophane and metionine. By good chose of vegetables, at athletes in which nutrition plant food dominates(vegetarians), satisfable intake of all amino- acids can be achieved.

Groceries that belong to two groups(pyramid model): milk and milk products, as the group meat, contain in their composition important amount of high value proteins. High proteine amount is also found in peas and beans grain, just as in stone fruit. Generally, vegetables, fruit and grain food contain proteins in their composition; but their content is small and it varies. In table below groceries are shown by groups and contain of proteins varies inside of them; good combination of groceries from various groups enables satisfactive intake of proteins.

Protein amount in some groceries
Groceries	Portion size	Proteins(g)
Meat, fish, chicken	120 g cooked	30
Egg	one big	7
Tuna	450g can	40
Beans, legumes	1 cup	7
Peanuts butter	2 spoons	9
Soya, cheese	120g	10
Milk or yoghurt	240g	8-10
Cheese, hard	30g	7
Rice, pasta, potatoes, dumplings	1 cup	2
Bread	1 piece	2
Peas, carrot, corn, beet root	1 cup	2
Fruit	1 piece	<1

Animal groceries contain high amount of high quality proteins, that at the same time contain a lot of fat. So it should be selective with food chosing and food preparation.

Protein digestion starts in gastric, and it is continued in intestinals under influence of pancreas enzymes. Then it comes to protein separation to polypeptids, and in the end amino acids. Amino-acids, built in the process of digestion, are absorbed in intestinals, and then through blood come to liver, where the most significant part of metabolism is done. In liver amino-acids are constantly synthetized, and they are used in synthesis processes in various tissues.

If amino-acids are not used for the process of protein synthesis, their further metabolism can flow in various ways:

1. Separating amino-group(NH₂) (disamination), fat acid is being created, which can be used in Krebs cycle for energy gaining.
2. The rest that is created by disamination can be used for synthesis of some carbohydrate or fat.
3. Amino-group, created by disamination, can be used for new amino-acids synthesis from the existing ones.
4. Amino-group, in chemical reaction with water and carbon dioxide, builds urea that is  secreted through urine. Amino-group can also take part in the build of ammonium salts that serve as a part of puffer system in kidney, or it is secreted from the organism through kidney.

Protein role in organism

The most important functions of proteins are:

1. Influence in various tissues(organs) creating.
2. Forming structural base for all enzymes in organism that control the speed of chemical reactions development.
3. Build antibodies.
4. Build chormones.
5. Help in water balance maintaining.
6. Their chemical structure and huge representation in organism makes them the most significant factor for maintaining acid-base balance.
7. Helping in process of blood cells forming.
8. Transport role is manifested in function of lipoproteins, haemoglobin(oxygen and carbon dioxide transport) and other proteins that take part in nutrients and metabolism products to various tissues transport.

Daily protein intake at healthy people that do not do any sport, should be 10-15% of maximum daily amount of calories. Recommendations in the countries of western Europe are 54-105g for grown-up males and 43-81g for females. In USA recommended daily amount is 0,8-0,9g for grown-ups. Daily protein needs vary depending on age and gender.

Daily protein needs dependant on age and type of physical activity
Number of grams by kg/BM
Standard, RDA, sedentary, grown-ups	0,8
Recreatives, grown-ups	1,0-1,5
Athletes, competitiors, grown-ups	1,2-1,8
Adolescents, athletes	1,6-1,8
Muscle mass build, grown-ups	1,4-1,8
Athletes on restrictive energy intake	1,6-1,8
Maximal grown-up amount	1,8

"Athletes' nutrition", Marina Djordjevic Nikic