Protein is one of the basic energy and building components of not only man but also every plant. Proteins constitute about 20% of the dry matter of the human body. This article describes what the protein is, what its functions, sources are and what are the consequences of excess and deficiency of this ingredient in the daily diet.
Definition and basic division of proteins
A protein is a multiparty nitrogen compound composed of amino acids that are linked together by peptide bonds. The protein consists of nitrogen, carbon, oxygen, sulfur, and hydrogen. Such proteins are called simple. Those that are also combined with other components that are not amino acids at the same time are called complex proteins. Compounds are composed of, among others, phosphate acid, and more precisely its residue, carbohydrates and even fats.
Physiological functions of proteins
One of the most basic functions of protein is the building function. Proteins are part of every cell of a living organism, it is an essential ingredient for growth and development.
Another very important function of the protein is the supply of energy, 1 g of protein provides about 4 kcal. The body breaks down and synthesizes proteins every day, which is why it is one of the three basic energy components of the diet.
As mentioned above, proteins are part of every cell of the living body, but not only. They are part of enzymes, antibodies, hormones (adrenaline, noradrenaline, thyroid hormones), thanks to which their role in the human body is huge. Because they build other chemical compounds, they affect cellular and humoral immunity, participate in metabolic processes, transport of oxygen, iron or vitamins.
Proteins are also the basic building block of muscle fibers. They are mainly responsible for their work, they are also necessary to repair damaged body tissues. They participate in vision processes because they transmit light stimuli. They also affect blood pH due to its buffering capacity.
The body’s needs for protein
Proteins undergo constant exchange in the body, which is why it is necessary to supplement them daily with diet. Everyone has an individual need for protein. In addition to the amount of protein, attention should also be paid to its quality. This involves the need to provide all the essential amino acids. What should you pay attention to when calculating the demand for this nutrient?
According to Polish standards, the appropriate level of protein fluctuates within 10-20% of the daily energy demand. In terms of grams, it is 0.8-1 g / kg body weight in adults (women and men). At the very beginning, you should estimate how many calories a given person should deliver during the day, taking into account their sex, age, height, weight, and physical activity – and on this basis calculate the percentage of proteins.
Physiological status and age
When estimating the right amount of protein, it is also important to determine the physiological state. This is necessary because physiological conditions such as pregnancy or lactation require a higher supply of protein. This is due to the construction of new cells, including the developing fetus, membranes, increase in lean mass. The need for protein in pregnant women is 1.2 g / kg body weight/day, while during lactation 1.45 g / kg body weight/day.
After the diseases, the demand for protein increases. Increased protein supply aims to cover the loss of lean (muscular) body mass that occurred as a result of the disease. Sometimes, however, in kidney diseases, with their failure, the amount of protein should be significantly reduced to improve the work of these organs.
The body mass index helps most accurately determine the protein requirement calculated directly on grams because standards for the Polish population precisely determine the number of grams of protein per kg of body weight. For example, a woman with a bodyweight of 60 kg should deliver 48 g of white during the day because about 1 kg of her body weight is about 0.8 g of protein.
People who exercise very often and intensively may, and even should increase the amount of protein during the day. It is associated with the increase of lean body mass and the need to repair muscle microdamage associated with intense physical exercise. For people practicing endurance sports, the recommended protein intake is 1.2-1.4 g / kg body weight, while endurance strength 1.4-1.8 g / kg body weight/day.
The nutritional value of the protein
It is important to determine what quality protein is needed and to include in the diet products that can cover the demand for all essential amino acids.
Sources of protein in food
At the very beginning, it should be mentioned that there are two types of proteins – wholesome and defective. Full-value proteins are those that provide all essential exogenous amino acids that the body can not synthesize on its own. Besides, wholesome proteins provide amino acids in such proportions that the body can maximize them for the synthesis of body proteins, growth processes, as well as to maintain the nitrogen balance. Defective proteins are compounds that are not used wholly for the synthesis of body proteins, growth needs or to maintain the aforementioned nitrogen balance.
So where will we find wholesome proteins? Primarily in animal products. Full-value proteins provide eggs, meat, fish, as well as milk and dairy products.
Deficiency proteins include the majority of plant products. They do not provide all essential exogenous amino acids, such as valine, tryptophan, lysine, and methionine. Among plant products, the greatest nutritional value is found in the protein seeds of all legumes. These include soybeans, peas, beans, chickpeas, and lentils.
Although vegetable proteins are not wholesome, it does not mean that they should not be included in the daily diet, quite the opposite. Why? Mainly because with meals we usually provide a mixture of various amino acids (remember that even carbohydrate products provide us with proteins). During digestion and absorption, the body uses the phenomenon of amino acid supplementation, consequently increases the nutritional value of a meal or a 24-hour food ration. This is a beneficial phenomenon when planning vegetarian or vegan diets, where the choice of meat and animal products is limited.
Consequences of deficiency or excess of protein in the diet
In healthy people, protein deficiencies are very rare and are usually the result of a poorly balanced diet. In Poland, as in most countries of the world, the opposite situation is observed, i.e. increased intake of this macroelement. Insufficient protein supply is most often observed with increased demand caused by stress, infection or increased protein loss as a result of burns, diarrhea or hemorrhage.
It is also worth remembering one very important thing. Protein metabolism in the human body is closely related to the energy supply in the diet. Simply put, it means that if a given person provides too few calories with a diet, including a small amount of this energy comes from the supply of carbohydrates and fats, the body begins to intensively use protein as a source of energy. It impairs the protein economy, protein malnutrition and dysfunction of the body. It is worth thinking about it before we start to lose weight and use a low-calorie diet.
Long-term starvation leads to malnutrition called marasmus. This malnutrition is manifested by a high weight loss, including the loss of both fat and lean tissue (ie muscle), anemia, and immunity decline, because, as is already known, the protein is used to synthesize antibodies. There is also a disturbance of the function of digestion, absorption, breathing and even circulation.
In children, such diets may inhibit the growth and development of the body. Undernutrition may be caused by an insufficient supply of food associated with a bad economic situation or as a result of post-operative conditions, injuries or prolonged fasting for various reasons.
The second complication associated with inadequate protein supply is kwashiorkor malnutrition. Kwashiorkor occurs when the amount of protein is inadequate to the level of energy supplied. This malnutrition can be noticed by observation of typical symptoms, such as edema, fatty liver, hair color change, skin, and in children, inhibition of growth and development.
There are also cases of excessive protein intake exceeding the amount necessary for the synthesis of body proteins and nitrogen compounds. In this situation, increased catabolism, i.e. the breakdown reaction, as well as the increased use of protein as an energetic material is observed. What are the consequences for health? Above all, large, non-physiological amounts of protein supplied with the diet cause damage to the kidneys, increase the risk of osteoporosis, acidosis and kidney stones.
Protein plays a very important role in every living organism. Without protein, we would not be able to manage or function properly. However, as with everything, so with the amount of protein in the diet can not be overdone. It’s good to take into account the products that provide wholesome forms of protein when composing a menu so that we can cover the need for all essential exogenous amino acids.