Proteins can be obtained from both animal foods and plant foods. These sources have certain advantages and disadvantages:

• animal protein is rich in B vitamins, zinc and iron;

• also, animal sources, especially wild salmon, contain polyunsaturated fatty acids;

• plant-based foods contain a large amount of fiber, which has a positive effect on the digestive system;

• in addition, they contain a large number of vitamins and beneficial microelements;

• animal sources are high in calories and high in cholesterol, and abuse of such products can lead to the formation of malignant tumors;

• but with the help of plant proteins it is quite difficult to obtain all the essential amino acids in sufficient quantities.

All proteins are polymers whose monomers are amino acids. They are mainly composed of carbon, hydrogen, oxygen and nitrogen. In the majority of the studied proteins of all living organisms, 20 amino acids were identified that were involved in their construction.

In the human body, this element performs five important functions:

• Recovery (being a “building material” for cells, ensures their normal development);
• Saturation with energy (the body uses it as a source of energy, subject to sufficient consumption);
• Transport of molecules (for example, hemoglobin, which saturates all tissues and organs with oxygen);
• Protection (sufficient protein intake has a positive effect on the immune system);
• Carrying out chemical reactions in the body (some of them are simply impossible without the participation of this element).

This organic substance is especially necessary during pregnancy. It is actively used for the development of a healthy fetus. It should also be consumed in sufficient quantities during puberty, recovery and rehabilitation after illnesses and injuries.

Proteins are solid substances that have a crystalline or amorphous structure. They have different solubility in liquid media. They are:

• fat-soluble;

• water-soluble;

• soluble in saline solutions, etc.

The classification of proteins is based precisely on their solubility. More often they have no color or have a white tint. If the protein has a color, it means that it contains components found in metals (for example, copper or iron).

From a chemical point of view, proteins have a specific molecular structure. They are divided into a huge number of different groups with a complex system of connections at the chemical level. That is why their physicochemical properties are so diverse.

The chemical properties of proteins include:

• combustion with the release of a characteristic odor. It smells like “burnt horn or bone.” If such a reaction exists, then we are talking about a qualitative reaction, on the basis of which the animal and plant origin of a substance are distinguished;

• decomposition at low temperatures.

Separately, it is worth mentioning the ability of proteins to hydrolyze. First, the system that contains the protein enters into the coagulation process (we are talking about a colloidal system). Next, the molecular structure of proteins is destroyed. Catalysts in the form of the enzymes pepsin and trypsin enter into the reaction, and hydrolysis itself occurs under acidic conditions with the destruction of primary protein structures.

There are nine amino acids that are essential. Each of them is found in certain products and is valuable in its own way for humans:

• valine. Helps the tissues of our body to fully develop. Responsible for the most important bodily functions – in particular, coordination of movements. Valine is contained in almost all types of fish, as well as meat, dairy products, nuts, seeds and dried herbs;

• leucine. Responsible for the growth and development of muscles and connective tissue, regulates the amount of sugar in the bloodstream, promotes rapid healing of the skin from wounds and injuries. Like valine, leucine is found in fish, meat, legumes, nuts and cereals;

• threonine. Ensures the production of elastin and collagen, which are responsible for the elasticity and youth of the skin. In addition, threonine takes an active part in the activity of the immune system. A person gets this amino acid from fish, mushrooms, meat and cereals;

• methionine. Participates in digestive processes, helps the body process fats, and provides it with protection from toxins and poisons. They are rich in eggs, meat, liver, legumes, soybeans and all types of nuts. There is methionine in unprocessed rice, wheat, oatmeal, buckwheat, semolina, barley;

• tryptophan. Thanks to him, we sleep soundly and fully. With enough tryptophan, a person almost always has a stable mood and a good appetite. This amino acid is contained in cheeses, all types of nuts, rabbit and turkey meat, fish, dairy products, millet and buckwheat;

• lysine. Without it, we cannot absorb calcium. The human body produces enzymes and hormones with the active participation of lysine. Thanks to it, muscle tissue becomes stronger and more resilient, memory becomes sharper, and hair becomes stronger. Lysine is found in red meat, chicken, fish, dairy products, and potatoes. It also contains soy, nuts, lentils and wheat;

• phenylalanine. Helps improve mood, reduce pain, improve memory processes and reduce appetite. Eggs, beef, fish, soybeans, nuts, milk and milk products are rich in phenylalanine;

• arginine. Slows down the development of tumor processes, has a beneficial effect on metabolic processes in muscle tissue, and regulates blood pressure. It is found in pumpkin seeds, rice, peas, buckwheat, chicken, pork, high-fat milk;

• histidine. Ensures proper functioning of joints, restores tissue and even auditory processes. It is found in cereals and legumes, nuts, and meat.

Amino acids are organic compounds that are part of all tissues of the human body. They are responsible for metabolic processes and energy metabolism, ensuring the functioning of the body. Amino acids directly affect the state of the nervous system, regulating mental activity, mood and sleep.

These components are necessary for the formation of muscles, tendons and ligaments, as well as hair and skin. Without a sufficient amount of amino acids, active growth of muscle mass is impossible. In sports and fitness, amino acids increase the performance of an athlete and accelerate the process of building muscle mass. They help you recover faster after hard workouts and relieve muscle pain.

Beneficial properties of amino acids [1, p. 14]:

• creation of new cells;
• tissue regeneration;
• immune support;
• increase in muscle mass;
• normal course of metabolic processes;
• getting rid of excess weight;
• strengthening the nervous system and increasing concentration;
• providing the body with additional energy;
• improvement of the condition of skin, nails, hair.

Amino acids have antioxidant properties. These substances significantly slow down the aging process, keeping the skin young and elastic. They also stimulate sexual desire and increase libido.

All amino acids are divided into essential and non-essential. There are also partially replaceable substances that are synthesized in the human body in insufficient quantities. They can only be produced under certain conditions or during a certain age period.

Partially replaceable substances include cysteine, histidine, tyrosine, and arginine, which is not produced in children and adolescents. Sources of partially essential amino acids include lean meats, soybeans, peanuts, pumpkin seeds, cheese and lentils[2].

For proper functioning, the body uses 22 amino acids, of which 10 substances are synthesized independently. The remaining 9 components must be obtained from food or dietary supplements. The diet should also contain foods rich in partially essential amino acids[2].

Essential amino acids (BCAAs) are substances that are not produced by the human body. They can only come from food or synthetic food additives.

The category of essential amino acids includes 9 substances[3]:

• valine – a stimulant important for muscle metabolism and recovery after training;
• histidine is part of hemoglobin, stimulates tissue growth and repair;
• leucine – characterized by an anabolic effect, protects muscle tissue, and is also effective in the treatment of arthritis;
• isoleucine – promotes the formation of hemoglobin, accelerates muscle growth, helps cells absorb glucose;
• threonine – responsible for the balance of protein compounds in the body;
• methionine is a hepatoprotector and has a metabolic effect;
• lysine – has bactericidal properties, strengthens the immune system;
• tryptophan – an immunoprotector, participates in the synthesis of the hormone of happiness – serotonin;
• Phenylalanine is an important component used in the treatment of many diseases (vitiligo, ADHD, depressive disorders).

Nonessential amino acids include substances that are synthesized by the body itself. They are mainly produced in the liver.

List of essential amino acids[3]:

• asparagine – is involved in the production of ammonia and is necessary for the normal functioning of the nervous system;
• alanine – part of proteins and biologically active substances;
• proline – is an integral part of the collagen protein;
• glycine – part of biologically active compounds, acts as a receptor in the brain and spinal cord;
• carnitine – participates in the transport of fatty acids;
• taurine – plays an important role in lipid metabolism, accelerates wound healing;
• serine – a building material for creatine, is involved in the transformation of glycogen;
• ornithine – has anti-catabolic properties, used in sports medicine;
• glutamine – ensures muscle growth and strong immunity;
• glutamic acid – acts as a receptor.

Amino acids are necessary for athletes and ordinary people. These substances perform many important functions in the human body. Amino acids help you lose weight because they regulate metabolism and ensure the proper functioning of the digestive system.

The importance of amino acids for athletes cannot be overstated. With a lack of amino acids, it is difficult to imagine gaining muscle mass, effective training process and recovery from injuries.

Amino acids are found in most traditional foods and are also available as dietary supplements. The substances are safe to use and do not cause addiction or negative side effects.