Macronutrients (II)

In the previous presentation we learned that macronutrients are responsible for supplying the energy needed to breathe, grow, maintain temperature, repair tissues, among many other functions. We also explained that both deficits and excesses of energy cause health disorders in children that can become irreversible and have repercussions in later stages of their lives.

We also learned that simple carbohydrates such as table sugar and sweets when consumed in excessive amounts can lead to diseases such as Diabetes Mellitus type 2. In this presentation we will study what proteins are and what functions they perform in our organism. We will also learn which are the foods that provide the highest amounts of proteins and which are the best quality protein sources.

Proteins

Proteins are large molecules (macromolecules) formed by linear chains of amino acids that are part of all living tissues, constituting the basis of proteins. The arrangement or sequence of these amino acids determines the structure and function of the different proteins.

Protein functions

• Plastic or structural function: They are the fundamental structural component of all cells and tissues; therefore, they are essential for the growth, repair and continuous renewal of body tissues.

• Contractile function: They allow muscle contraction. Example: Myosin, which is the most abundant protein in skeletal muscle, together with actin, allow muscle contraction.

• Transport function: Proteins allow substances to be carried through the organism to where they are required. For example: hemoglobin is a blood protein responsible for transporting oxygen from the respiratory organs to the tissues; and carbon dioxide from the tissues to the lungs, which eliminate it.

• Defensive function: They fulfill defense functions of the organism. For example: Glycoproteins are in charge of producing immunoglobulins that defend the organism against foreign bodies and keratin is the protein in charge of protecting the skin.

• Enzymatic function: They intervene as facilitators of the chemical reactions of cellular metabolism, facilitating the digestion and absorption of food. For example: Sucrase is responsible for converting common sugar into glucose and lactose, making digestion possible. The absence of sucrase causes sucrose intolerance.

• Energy function: Although they are not usually an important energy source, proteins can also provide energy to the body, especially in situations of long-term exercise or prolonged fasting.

Which proteins are of higher quality?

In general, the evaluation of protein quality is based on the estimation of the proportion of absorbed protein that is retained and used by the body. According to this criterion the proteins can be evaluated as:

• Protein of high biological value: these are proteins that contain all the amino acids that man needs in the right proportions. In general, proteins with high biological value are of animal origin since their amino acid composition is more similar to body proteins. Foods rich in proteins with the highest biological value are breast milk, eggs, fish and meat.

• Protein of lower biological value: Proteins that do not contain all the amino acids that humans need in the right proportions. The proteins of lower biological value are of vegetable origin, since in their composition they do not contain the necessary quantities of some amino acids. Foods rich in proteins of lower biological value are soybeans, corn, peanuts, oats, chickpeas and brown rice.

Circumstances that lead to an increase in the body's protein demand

Pregnancy: The development of maternal and fetal tissues requires a considerable protein content in the diet of the pregnant woman, which increases as the pregnancy progresses.

The lactating mother: It is estimated that to synthesize one gram of breast milk, the mother must use two grams of proteins from the diet; therefore, protein deficiencies in the lactating mother's body reduce the quality of breast milk.

Rapid growth phases: During phases in which there is a significant increase in the growth of organs and tissues, the organism demands a greater number of proteins from the diet to be used in the formation of new cells and tissues.

The most accelerated phases of child growth are:

• In the prenatal phase.

• During the first months and up to three years of age.

• During adolescence.

The realization of intense physical activities on a regular basis: Children who exercise or practice sports on a daily basis need to increase protein intakes depending on the rigor of the physical activity.

Suffering and convalescence from illness: From the moment of diagnosis of some diseases and throughout their evolution, the increase of protein intakes constitutes one more tool for their treatment. Specialists should recommend increases in protein intakes and periodically adjust them according to the evolution of the disease.

As already explained, the recommendations for energy, protein and other nutrients for each infant stage will be specified later in this course.

Risks of following protein-deficient diets

• May cause anemia due to disorders in the production of red blood cells, since proteins are involved in their manufacture.

• More frequent viral and infectious diseases due to the weakening of the immune system.

• Learning disorders and mental retardation in children.

Risks of following diets with protein excesses

• Can lead to obesity because excess protein is used to meet energy demand or stored as fat.

• The excessive consumption of proteins during long periods of time could cause affections in the liver and kidneys.