Proteins

The human diet consists of many components. They are divided into macronutrients – proteins, fats, and carbohydrates, as well as micronutrients – vitamins, minerals, etc. Proteins provide approximately 10-15% of the daily energy intake. 1 gram of protein releases 4 kcal. Proteins are the main building material of the body. Proteins are broken down into amino acids, which are important for the renewal of muscles, bones, skin, blood, and other vital systems. In addition, they are used in the synthesis of nucleic acids carrying genetic information.

In adult organisms, proteins make up about 16% of body mass. Of these, 43% are in muscles, 15% in the skin, 16% in blood composition, etc. Functions of proteins in the human body:
• Structural. About half of the proteins in the body play a “structural” role, for example, in the skin, muscles. These proteins are collagen, actin, and myosin.
• Transport. Proteins help transport many nutrients through the blood and other body fluids, such as hemoglobin, lipoproteins.
• Hormonal. Hormones are amino acid chains that form peptides, such as insulin.
• Enzymatic. All enzymes are proteins. For example, the digestive enzyme amylase, etc.
• Immune. Antibodies are protein molecules. Proteins also participate in suppressing inflammatory reactions.
• Protective. The protein albumin performs a protective function, maintaining the necessary blood pH.
Proteins are classified by their nutritional value into complete and less valuable. Their value depends on the complex of amino acids that the human body absorbs best. This “complex” changes depending on the physiological development of the individual.
Proteins are made up of amino acid chains. Amino acids bond together to form peptide chains, more than 10 amino acids form polypeptides.

Essential Amino Acids
Some amino acids can be produced by the body, while others must be obtained from food. There are eight indispensable amino acids.

The importance of certain amino acids depends on the stage of human physiological development. For example, in childhood, some amino acids are very important, which is not important for adults (arginine, histidine, cysteine, glycine, tyrosine, glutamine, proline). These amino acids are very important in the growth period of children because the child’s body does not synthesize them due to increased demand. During metabolic stress, glutamine synthesis may be insufficient, so in such cases, it becomes indispensable.
Amino acids determine the biological value of proteins. Proteins that contain all essential amino acids in sufficient quantities have a high biological value. Proteins of high biological value are found in animal sources: meat, eggs, dairy products, fish. If one or more essential amino acids are missing in proteins, their biological value is low. Usually, plant-based proteins have low biological value. If the nutritional value of the daily diet is too low, the body’s proteins are used to produce energy. Protein deficiency often occurs in patients undergoing surgery and in older adults. Protein deficiency manifests in kidney diseases, severe injuries, burns, sepsis, malabsorption cases. Protein deficiency causes muscle wasting, poor wound healing, susceptibility to infections, edema, liver dysfunction.

Source | Dietary Treatment in General Practice | Dietitian Doctor Jūratė Dobrovolskienė