Proteins in nutrition

The appropriate protein content in our diet is vital, since all living tissues contain proteins, some are structural such as collagen, others are enzymatic such as sucrose, and others such as insulin are hormones.

Proteins determine the shape and structure of cells, allow them to maintain their integrity, control and regulate their functions, and protect them from external agents.

Proteins are macromolecules that are made up of a large number of simple repeating units, called amino acids, linked by peptide bonds. They are distinguished from lipids and carbohydrates because they contain nitrogen.

Amino acids are organic molecules that form the basis of proteins.

Classification of amino acids: they are divided into two groups according to their capacity to be synthesized or not, by our organism.

Essential or indispensable amino acids: they cannot be synthesized by the organism so they have to be provided by food. These amino acids are: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.Non-essential amino acids: these can be synthesized by the body. Protein functions:

• Plastic or structural function: they participate in the formation of support and filling tissues, providing resistance and elasticity. They are also part of chromosomes and cell membranes. Example: collagen, the most abundant protein molecule in skin and bones. It is responsible for the great resistance of human tendons.

• Enzymatic function: they intervene as biocatalysts in the chemical reactions of cell metabolism. Example: sucrase, responsible for converting common sugar into glucose and lactose. The absence of sucrase causes sucrose intolerance.

• Regulatory function: they participate in some chemical reactions that take place in the organism. They serve to regulate cell division and the expression of certain genes.

• Homeostatic function: they maintain equilibrium and participate in the regulation of the concentration of hydrogen ions present in certain solutions in the internal environment.

Protein functions:

• Defensive function: they perform defense functions of the organism. Examples: Glycoproteins, responsible for producing immunoglobulins that defend the organism against foreign bodies. Keratin, which protects the skin.
• Hormonal function: some hormones are of protein nature. Insulin, for example.
• Contractile function: they allow muscle contraction. Example: myosin, together with actin, allows muscle contraction.
• Transport function: they allow substances to be carried through the organism to where they are required. Example: hemoglobin, which carries oxygen through the blood.
• Reserve function: in necessary cases, when the diet does not provide sufficient fats or carbohydrates, protein will be used to provide energy. Example: in cases of starvation.

The biological value of protein (bv): is defined as the proportion of absorbed protein that is retained by the body. According to this criterion proteins can be evaluated as:

• Protein of high biological value: these are proteins that contain all the essential amino acids in the proportions necessary for man. They are usually of animal origin. Examples: proteins from breast milk and chicken eggs.

• Protein of lower biological value: proteins that contain small amounts of some of the essential amino acids. They are generally of vegetable origin. Examples: proteins from cereals, legumes and nuts.

Protein requirements at different stages of life:

• Pregnancy: the development of maternal and fetal tissues requires a protein supplement in the diet of the pregnant woman. Increases between 15 grams per day and 25 grams per day are recommended over the diet of healthy non-pregnant women.

• Breastfeeding women: to convert the proteins in the mother's diet into proteins in breast milk, it is recommended to maintain the protein intake during pregnancy, which would mean an increase of about 25 grams per day over the diet of healthy non-breastfeeding women.

• Childhood: protein needs are high, mainly due to the growth of all organs and systems.

• Adolescence: during adolescence the body maintains high protein needs, justified by the high level of growth of muscle and bone mass.

• Adulthood: it is recommended to ingest between 0.8 grams and 1 gram of protein per kilogram of weight per day.

• Senescence: it is recommended to maintain the protein intake levels of the adult stage as long as the organism remains healthy.

Some consequences of protein deficiency in the body:

• Anemia may appear due to disorders in the production of red blood cells since proteins are involved in their manufacture.

• Suffering from infections due to weakening of the immune system.

• Learning disorders and mental retardation in children.

Some consequences of excess protein in the body:

• It can cause loss of bone mass due to loss of calcium.

• Cardiovascular disorders due to the fact that most proteins are accompanied by saturated fats that increase cholesterol levels.

• Obesity, because excess protein can affect the process of fat assimilation.

• It can affect the liver and kidneys since excess protein generates an overload of waste substances such as ammonia and uric acid.