Protein: Distribution, Functions, Demands, Deficiency, and Excess

Proteins are intricate nitrogen compounds composed of amino acids that are bonded together by peptide bonds. Among the components of proteins, we can distinguish nitrogen, carbon, oxygen, sulfur, and hydrogen. Such proteins are referred to as simple proteins. However, there are also complex proteins that, in addition to the aforementioned components, also contain other substances, such as phosphoric acid, carbohydrate residues, or fats.

One of the fundamental functions of proteins is the structural function. They are a component of every living organism's cell, they are indispensable for growth and development. Another important function of proteins is to provide energy, 1 gram of protein provides about 4 calories. The human body undergoes protein degradation and synthesis daily, making it one of the three fundamental energy components of the diet. As previously mentioned, proteins are essential for every living cell, but not just for that. They are a component of enzymes, antibodies, hormones (adrenaline, noradrenaline, thyroid hormones), making their role in the human body significant. Since they are an integral part of other chemical compounds, they influence cellular and humoral immunity, participate in metabolic processes, oxygen, iron, and vitamin transport. Proteins are also a basic component of muscle fibers. They are primarily responsible for their function and are essential for repairing damaged tissue in the body. They also participate in visual processes, as they transport light signals. They also have an influence on blood pH due to their buffering capacity.

Proteins undergo constant breakdown and synthesis in our bodies, hence the need for their regular replenishment through food. Protein requirement is variable and depends on various factors such as age, physical activity, health status, and body weight. In addition to the quantity of protein, its quality is also important, which involves the need to supply all the essential amino acids. What aspects should be considered when calculating protein requirement?

According to Polish standards, the corresponding level of protein fluctuates within the limits of 1020% of the daily caloric requirement. In grams it is 0.81 g/kg of body weight in adults (women and men). At the very beginning, it is necessary to estimate how many calories a person should provide during the day, taking into account their gender, age, height, body weight and physical activity and calculate the percentage of protein on this basis.

Determining the appropriate protein quantity also necessitates considering the physiological state. This is required as physiological states such as pregnancy or lactation necessitate an increased protein provision. This is due to the development of new cells, including the developing fetus, fetal membranes, as well as an increase in fat-free weight. The protein requirement for pregnant women is 1.2 g/kg body weight/day, while during lactation it is 1.45 g/kg body weight/day.

Upon surviving an illness, the protein requirement escalates. The augmentation of protein supply aims to offset the loss of fat-free body mass, which was caused by the illness. However, in specific instances of renal disorders, during their failure, it is imperative to substantially curtail the protein quantity to enhance the operation of these organs.

The body weight gauge is the most precise way to determine protein requirements in grams, as the standards for the Polish population accurately define the number of grams of protein per kg of body weight. For instance, a woman with a body weight of 60 kg should consume around 48 grams of protein daily, as 1 kg of her body weight requires approximately 0.8 grams of protein.

Those who frequently and highly intensely train may and should increase their protein intake during the day. This is due to the increase in muscle mass and the need to repair minor muscle injuries resulting from intense physical exertion. For endurance athletes, a protein intake of 1.2-1.4 g/kg body weight is recommended, while strength-resistance athletes should consume 1,4-1,8 g/kg body weight daily.

The primary task involves determining the necessary quality of protein and incorporating products into the diet that are able to meet the requirement for all essential amino acids.

At the outset, it is worth noting that there are two types of proteins: complementing and incomplete proteins. Complementing proteins provide all the essential amino acids that the body cannot synthesize on its own. Additionally, complementing proteins supply amino acids in such quantities that the organism can make the most of them for the synthesis of body proteins, growth processes, and nitrogen balance. Incomplete proteins, on the other hand, are compounds that are not fully utilized for the synthesis of body proteins, growth needs, or maintaining the aforementioned nitrogen balance. Complementing proteins are mainly found in animal products such as eggs, meat, fish, milk, and dairy products. However, incomplete proteins are present in most plant-based products that do not provide all the necessary exogenous amino acids such as valine, tryptophan, lysine, and methionine. Nevertheless, this does not mean that plant-based proteins should not be included in the daily diet, as we usually consume a mix of different amino acids with meals. During digestion and absorption, the body utilizes the phenomenon of amino acid complementation, which increases the nutritional value of the meal or the daily food intake. This is particularly important when planning a vegan or vegetarian diet.

In healthy individuals, protein deficiencies are very rare and are usually the result of a poorly balanced diet. However, in Poland, as in most countries around the world, the opposite situation may be observed, i.e. increased intake of this macronutrient. Inadequate protein intake is most often observed with increased organisational demand caused by stress, infection or increased loss of protein as a result of inflammation, diarrhoea or bleeding. It is also important to note that the metabolism of proteins in the human body is closely related to the energy intake in the diet. If an individual does not receive enough calories from the diet, especially if only a small amount of energy comes from the intake of carbohydrates and fats, the body begins to use proteins as an intense source of energy, which affects the protein economy and leads to protein deficiency and functional disorders of the body. Long-term fasting can lead to malnutrition known as marasmus, which manifests as a significant weight loss, including the breakdown of fat and muscle tissue, anaemia, reduced immunity and disorders of the digestive, absorptive, respiratory and circulatory systems. Such diets can inhibit the growth and development of children. Malnutrition can be caused by inadequate food intake due to poor economic conditions or may be the result of postoperative conditions, injuries or long-term fasting for various reasons. The second complication associated with inadequate protein intake is malnutrition of the kwashiorkor type, which occurs when the protein amount is insufficient to meet the energy demand. It can be identified by observing typical symptoms such as oedema, fatty liver, changes in hair and skin colour and delayed growth and development in children. Excessive protein intake, which exceeds the amount required for the synthesis of body proteins and nitrogen compounds, leads to increased catabolism, i.e. a breakdown reaction, and to increased use of proteins as an energy source. Large, non-physiological amounts of proteins supplied with the diet can lead to kidney damage, increased risk of osteoporosis, acidosis and kidney stones.