Proteins are macromolecular compounds consisting of amino acid residues connected by peptide bonds. The main elements that make up proteins are: carbon, oxygen, hydrogen, nitrogen and sulfur. Proteins may also contain other elements, including: phosphorus, iron, zinc, copper, manganese, magnesium and iodine.


Protein is one of the three basic nutrients necessary for the proper functioning of the body. It consists of many amino acids and acts as a building block in the body, constituting about 20% of the human body weight, shaping connective tissue, muscles, bones, hair, teeth and nails.


Some proteins dissolve in water, some in aqueous solutions of acids, bases and salts, while none dissolve in organic solvents (except alcohol). At higher temperatures, as well as by the action of strong acids and bases, heavy metal salts or alcohol, the protein becomes curdled, i.e. the so called denaturation (under normal conditions, an irreversible process of changing the structure of a protein molecule).


The human body does not store proteins and amino acids: each supply of this ingredient is constantly used in the processes of growth, development and regeneration.

The demand for protein depends on many factors, including: health condition, age, the state of the body’s energy management, physical activity, physiological condition, and gender.


The amount of 2 g per 1 kg of body weight is the maximum that the human body can metabolise without overloading the kidneys and liver.


Protein demand in the human body

healthy person- 1 g of protein per 1 kg of body weight,

pregnant woman- 1.5 protein per 1 kg of body weight,

breastfeeding woman- 1.3 g of protein per 1 kg of body weight,

infants- 1.52 g of protein per 1 kg of body weight,

children up to 15 years of age- 1.5-1.7 g of protein per 1 kg of body weight,

people practicing sports- 1.5-2 g of protein per 1 kg of body weight,

fat tissue loss- 1.6-2.0 g of protein per 1 kg of body weight,

weight gain- 1.8-2.0 g of protein per 1 kg of body weight.

Reference proteinreference aminogram, characterised by the most appropriate content of individual amino acids (contains a full supply of amino acids) optimal for the needs of the human body. By comparing the amino acid composition of the protein with the composition of the reference protein, we obtain the biological value of the protein.

The standard protein for humans is found in chicken eggs,

and for infants in mother’s milk.

The nutritional value of protein depends on:

content of exogenous and endogenous amino acids,

mutual proportions between exogenous amino acids,

digestibility of protein products.

Types of protein

complete proteins: provide the body with the necessary amino acids in the right amount (they have a set of 8 exogenous amino acids);

incomplete proteins: do not contain all essential amino acids or contain them in small amounts (the content of exogenous amino acids is insufficient, less than 8 or the proportions between these amino acids are suboptimal).

Animal proteins are better absorbed than plant proteins because their amino acid composition is more similar to the proteins of the human body.

Proteins can be divided into:

structural proteins (collagen, elastin, keratin, glycoproteins),

enzymatic proteins (enzymes),

protective proteins (immunoglobulins, fibrinogen, interferon),

transport proteins (hemoglobin, plasma albumins, lipoproteins, transferrin),

contractile proteins (actin, myosin),

hormonal proteins (insulin, glucagon, parathyroid hormone, calcitonin),

storage proteins (myoglobin, ferritin),

receptor proteins,

cell membrane proteins.

Simple and complex proteins:

simple proteins are compounds consisting of many amino acids;

complex proteins are made of amino acids and additionally contain other components, such as sugars, lipids and metals.

Simple proteins:

albumins- dissolve in water, are found in muscle tissue and blood plasma;

globulins- dissolve in dilute salt solutions, occur in body fluids;

glutelins- dissolve in alkalis and acids;

histones- they are strongly alkaline, they dissolve in water;

prolamins- typical plant proteins found in seeds;

protamines- highly soluble in water;

scleroproteins- proteins with a fibrous structure, e.g. keratin.

Complex proteins:

phosphoproteins- containing a phosphoric acid residue in their structure, e.g. casein;

glycoproteins- contain sugars (covering tissue and body fluids);

chromoproteins- contain a pigment part, e.g. hemoglobin or rhodopsin;

lipoproteins- containing fat (cell membrane, blood plasma);

nucleoproteins- associated with nucleic acid;

metalloproteins- associated with a metal atom/cation.

Protein functions in the human body


energy source: burning 1 g of protein produces 4 kcal,

building blocks: used to build and rebuild muscle tissue, is a building component of bones and teeth as well as skin, hair and nails; construction and synthesis of new cells,

regenerative: tissue repair,

enzymatic and hormonal: production of enzymes and participation in the synthesis of hormones necessary to regulate processes occurring in the body,

immunomodulatory: production of white blood cells used to defend against pathogens,

transport: transport of substances in the body, they are a carrier of some vitamins and minerals,

regulating: maintaining the appropriate fluid balance and pH of blood and other fluids in the body (water and acid base balance), helps regulate the metabolic economy in the body,

defense: takes part in the production of antibodies of the immune system,

necessary in the wound healing process,

they determine the proper growth and development of the body,

are the basic component of blood, lymph and milk,

participation in the proper functioning of the digestive system.

Protein digestion



(the acidic environment of gastric juice causes denaturation- a change in the structure and loss of biological properties of proteins


(multi stage digestive processes leading to the form of free amino acids)

section of the small intestine

(absorption of digested protein components)

blood of the portal vein

(protein digestion products are carried by the blood to all tissues and are used for the synthesis of body proteins)


(the body directs proteins to appropriate places)

Protein deficiency in the body is called hypoproteinemia. Protein deficiency in the diet results in inhibition of growth and development of the body, prevents tissue reconstruction, hinders wound healing, reduces metabolism, immunity, well being, condition of skin, hair and nails, and disrupts thought processes and brain functioning.


The causes of protein deficiency are:

intestinal diseases,

poorly balanced diet,

liver disease,

skin damage,

kidney disease,

congenital plasma protein deficiencies,

the use of long term fasts.


Protein deficiency symptoms:

fatigue, weakness,

problems with concentration,

weakening of the immune system,

mood swings,

problems with sleeping,

loss of muscle mass,

hair loss,

dry skin,

brittle nails.


Long term protein deficiency may lead to protein malnutrition (kwashiorkor)- a decrease in the muscle mass of the heart and leading to disturbances in its contractility; liver damage and fatty tissue.

Excess protein in the diet results in accelerated filtration and excretion of minerals, and the risk of kidney stones increases. Increased protein intake burdens the kidneys and liver- due to the need to excrete nitrogen from the body (which will not be used to build proteins and is converted into urea and ammonia).


The causes of excess protein are:

following a high protein diet,

consuming large amounts of protein supplements,

following a slimming diet based on proteins and giving up fats and carbohydrates.


Symptoms of excess protein:



migraine headaches

acidification of the body,

risk of allergic reactions,

acne severity,

stimulating skin inflammation.


Excess protein impairs kidney function, which may lead to calcium or urate urolithiasis. It is possible to develop swelling, atherosclerotic lesions, potency disorders, and impaired calcium absorption.

Protein in the diet


Product and amount of protein in 100 g

beef ligawa 22

cocktail shrimps 27

chicken breast 21.6

smoked salmon 21.6

boneless pork loin 21

smoked mackerel 20.8

beef shoulder 20.9

fresh halibut 20.2

veal schnitzel 20.6

fresh salmon 20

pork liver 20.3

smoked sprat 19

pork tenderloin 20.2

fresh mackerel 18.8

duck breast 20

fresh rainbow trout 18.7

turkey thigh meat 19.5

fresh cod 17.8

turkey breast 19.3

frozen pollock 17.5

chicken liver 19.2

fresh pollock 16.7

veal liver 18

herring fresh 16.4

chicken thigh meat 17.9

fresh tuna 14.6

fresh mussels 12

full fat cheddar cheese 27.2

dry green lentils 25

fatty gouda cheese 25.2

cooked green lentils 12.1

full fat camembert cheese 21.5

dry yellow lentils 25

full fat brie cheese 19.9

cooked yellow lentils 10

full fat cottage cheese 18.8

sunflower seeds 24.4

chicken egg yolk 15.6

peas, dry seeds 23.8

egg white 11

peas, soaked seeds 12.6

granular cottage cheese 12.4

red beans, dry 23

processed cheese 7.6

soaked red beans 8.1

greek type yogurt 4.4

white beans, dry 21.4

natural yogurt 4.4

soaked white beans 7.1

kefir 3.6

blue poppy 20.1

milk 1.5% 3.4

dry chickpeas 20

buttermilk 3.4

canned chickpeas 6.3

tofu 12

frozen green peas 6.4

broad beans 5.2

quinoa 4

green beans 2.2

kale 2

broccoli 1.8

pistachios 20.6

oat groats 15

almonds 20

wheat groats 14

cashew nuts 18

buckwheat 12.6

walnuts 15.2

bulgur groats 12.5

hazelnuts 15

millet 10.5

pine nuts 14

semolina 8.7

brazil nuts 14

barley groats 8.4

peanuts 13.7

corn groats 8.3

pecans 9

brown rice 7.1

macadamia 8

white rice 6.7

Protein. Protein in the human body. Protein demand in the human body. Reference protein – reference aminogram. Protein division: complete and incomplete; simple and complex. Protein functions in the human body. Protein digestion. Protein deficiency, causes of protein deficiency, symptoms of protein deficiency, hypoproteinemia. Excess protein, causes of excess protein, symptoms of excess protein. Protein in the diet.