Features of metabolism at different age periods. Concept of metabolism and energy

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Introduction

As you know, metabolism and energy are the basis of life of all living beings. In most organs and tissues of the human body, new cells constantly die and are born, individual cellular elements and chemical compounds are synthesized and destroyed. The products of digestion of proteins, fats and carbohydrates, as well as vitamins, inorganic substances and drinking water act as building (plastic) material for new formations. At the same time, the vital activity and work of all systems and organs, all the construction and destructive processes of the body and, finally, the processes of external mental or physical work of a person will require energy expenditure. The source of energy, as well as the supplier of building materials, are consumer substances of food. Since the formation and destruction of biological structures, as well as the formation and expenditure of energy throughout life, occur continuously, simultaneously and in close interrelation, these processes are called metabolism and energy, or for abbreviation metabolism.

1. Metabolic processes

Metabolism and energy are the basis of the body's vital processes. In the human body, in its organs, tissues, and cells, there is a continuous process of synthesis, i.e., the formation of complex substances from simpler ones. At the same time, the breakdown and oxidation of complex organic substances that make up the cells of the body occurs.

The work of the body is accompanied by its continuous renewal: some cells die, others replace them. In an adult, 1/20 of the skin epithelial cells, half of all digestive tract epithelial cells, about 25 g of blood, etc. die and are replaced within 24 hours. The growth and renewal of body cells is possible only if there is a continuous supply of oxygen and nutrients to the body. Nutrients are precisely the building and plastic material from which the body is built.

For continuous renewal, the construction of new cells of the body, the work of its organs and systems - the heart, gastrointestinal tract, respiratory system, kidneys and others, energy is needed for a person to perform work. A person receives this energy through decay and oxidation during the metabolic process. Consequently, nutrients entering the body serve not only as plastic building material, but also as a source of energy necessary for the normal functioning of the body.

Thus, metabolism is understood as a set of changes that substances undergo from the moment they enter the digestive tract and until the formation of final breakdown products excreted from the body.

2. Anabolism and catabolism

Metabolism, or metabolism, is a finely coordinated process of interaction between two mutually opposite processes occurring in a certain sequence. Anabolism is a set of biological synthesis reactions that require energy. Anabolic processes include the biological synthesis of proteins, fats, lipoids, and nucleic acids. Due to these reactions, simple substances entering cells, with the participation of enzymes, enter into metabolic reactions and become substances of the body itself. Anabolism creates the basis for the continuous renewal of worn-out structures.

Energy for anabolic processes is supplied by catabolic reactions, in which molecules of complex organic substances are broken down to release energy. The end products of catabolism are water, carbon dioxide, ammonia, urea, uric acid, etc. These substances are not available for further biological oxidation in the cell and are removed from the body.

The processes of anabolism and catabolism are inextricably linked. Catabolic processes supply energy and starting materials for anabolism. Anabolic processes ensure the construction of structures that go towards the restoration of dying cells, the formation of new tissues in connection with the growth processes of the body; provide the synthesis of hormones, enzymes and other compounds necessary for cell functioning; supply macromolecules to be broken down for catabolic reactions.

All metabolic processes are catalyzed and regulated by enzymes. Enzymes are biological catalysts that “start” reactions in the cells of the body.

3. Forms of metabolism

Protein metabolism. The role of proteins in metabolism. Proteins occupy a special place in metabolism. They are part of the cytoplasm, hemoglobin, blood plasma, many hormones, immune bodies, maintain the constancy of the body’s water-salt environment, and ensure its growth. Enzymes that are necessarily involved in all stages of metabolism are proteins.

Biological value of food proteins. The amino acids used to build the body's proteins are unequal. Some amino acids (leucine, methionine, phenylalanine, etc.) are essential for the body. If an essential amino acid is missing from food, protein synthesis in the body is severely disrupted. Amino acids that can be replaced by others or synthesized in the body itself during metabolism are called non-essential.

Food proteins that contain the entire necessary set of amino acids for normal protein synthesis in the body are called complete. These include mainly animal proteins. Food proteins that do not contain all the amino acids necessary for protein synthesis in the body are called incomplete (for example, gelatin, corn protein, wheat protein). The highest biological value is found in the proteins of eggs, meat, milk, and fish. With a mixed diet, when the food contains products of animal and plant origin, the set of amino acids necessary for protein synthesis is usually delivered to the body.

The supply of all essential amino acids is especially important for a growing organism. For example, the absence of the amino acid lysine in food leads to stunted growth of a child and depletion of his muscular system. Valine deficiency causes vestibular disorders in children.

Of the nutrients, only proteins contain nitrogen, so the quantitative side of protein nutrition can be judged by the nitrogen balance. Nitrogen balance is the ratio of the amount of nitrogen received during the day from food and the nitrogen excreted from the body during the day through urine and feces. On average, protein contains 16% nitrogen, i.e. 1 g of nitrogen is contained in 6.25 g of protein. By multiplying the amount of absorbed nitrogen by 6.25, you can determine the amount of protein received by the body.

In an adult, nitrogen balance is usually observed - the amounts of nitrogen introduced with food and excreted with excreted products coincide. When more nitrogen enters the body from food than is excreted from the body, we speak of a positive nitrogen balance. This balance is observed in children due to an increase in body weight during growth, during pregnancy, and during heavy physical activity. A negative balance is characterized by the fact that the amount of nitrogen introduced is less than that removed. It can occur during protein starvation or severe illness.

Features of protein metabolism in children. In the child’s body, intensive processes of growth and formation of new cells and tissues occur. The protein requirement of a child's body is greater than that of an adult. The more intense the growth processes, the greater the need for protein.

In children, a positive nitrogen balance is observed when the amount of nitrogen introduced with protein foods exceeds the amount of nitrogen excreted in the urine, which ensures the growing body's need for protein. The daily protein requirement per 1 kg of body weight for a child in the first year of life is 4-5 g, from 1 to 3 years - 4-4.5 g, from 6 to 10 years - 2.5-3 g, over 12 years - 2-2.5 g, in adults - 1.5-1.8 g. It follows that, depending on age and body weight, children from 1 to 4 years old should receive 30-50 g of protein per day, from 4 to 7 years - about 70 g, from 7 years - 75-80 g. At these indicators, nitrogen is retained in the body as much as possible. Proteins are not stored in the body in reserve, so if you give them more with food than the body needs, then an increase in nitrogen retention and an increase in protein synthesis will not occur. Too little protein in food causes a decrease in the child’s appetite, disrupts the acid-base balance, and increases the excretion of nitrogen in the urine and feces. The child needs to be given the optimal amount of protein with a set of all the necessary amino acids, and it is important that the ratio of the amount of proteins, fats and carbohydrates in the child’s food is 1:1:3; under these conditions, nitrogen is retained in the body as much as possible.

In the first days after birth, nitrogen makes up 6-7% of the daily amount of urine. With age, its relative content in urine decreases.

Fat metabolism. The importance of fats in the body. Fat received from food in the digestive tract is broken down into glycerol and fatty acids, which are absorbed mainly into the lymph and only partially into the blood. Through the lymphatic and circulatory systems, fats enter adipose tissue. There is a lot of fat in the subcutaneous tissue, around some internal organs (for example, kidneys), as well as in the liver and muscles. Fats are part of cells (cytoplasm, nucleus, cell membranes), where their quantity is constant. Accumulations of fat can serve other functions. For example, subcutaneous fat prevents increased heat transfer, perinephric fat protects the kidney from bruises, etc.

Fat is used by the body as a rich source of energy. With the breakdown of 1 g of fat in the body, more than two times more energy is released than with the breakdown of the same amount of proteins or carbohydrates. A lack of fat in food disrupts the activity of the central nervous system and reproductive organs, and reduces endurance to various diseases.

Fat is synthesized in the body not only from glycerol and fatty acids, but also from metabolic products of proteins and carbohydrates. The main source of unsaturated fatty acids are vegetable oils. Most of them are in flaxseed and hemp oil, but there is a lot of linoleic acid in sunflower oil.

With fats, the body receives vitamins soluble in them (A, D, E, etc.), which are vitally important for humans.

For 1 kg of adult weight per day, 1.25 g of fat should be supplied from food (80-100 g per day).

The end products of fat metabolism are carbon dioxide and water.

Features of fat metabolism in children. In the child’s body, from the first six months of life, fats cover approximately 50% of the energy requirement. Without fats, it is impossible to develop general and specific immunity. Fat metabolism in children is unstable; if there is a lack of carbohydrates in food or with increased consumption, the fat depot is quickly depleted.

Fat absorption in children is intense. When breastfeeding, up to 90% of milk fats are absorbed, when artificial - 85-90%. In older children, fats are absorbed by 95-97%.

For a more complete use of fat, carbohydrates must be present in children’s food, since when they are lacking in the diet, incomplete oxidation of fats occurs and acidic metabolic products accumulate in the blood.

The body's need for fat per 1 kg of body weight is higher, the younger the child's age. With age, the absolute amount of fat required for the normal development of children increases. From 1 to 3 years, the daily requirement for fat is 32.7 g, from 4 to 7 years - 39.2 g, from 8 to 13 years - 38.4 g.

Carbohydrate metabolism.

Carbohydrates are the main source of energy, especially during intense muscle work. In adults, the body receives more than half of its energy from carbohydrates. The breakdown of carbohydrates with the release of energy can occur both in oxygen-free conditions and in the presence of oxygen. The end products of carbohydrate metabolism are carbon dioxide and water. Carbohydrates have the ability to quickly break down and oxidize. In case of severe fatigue or heavy physical exertion, taking a few grams of sugar improves the condition of the body.

In the blood, the amount of glucose is maintained at a relatively constant level (about 110 mg%). A decrease in glucose levels causes a decrease in body temperature, disruption of the nervous system, and fatigue. The liver plays a large role in maintaining constant blood sugar levels. An increase in the amount of glucose causes its deposition in the liver in the form of reserve animal starch - glycogen, which is mobilized by the liver when the blood sugar level decreases. Glycogen is formed not only in the liver, but also in the muscles, where it can accumulate up to 1-2%. Glycogen reserves in the liver reach 150 g. During fasting and muscular work, these reserves are depleted.

The importance of glucose for the body is not limited to its role as an energy source. It is part of the cytoplasm and is therefore necessary for the formation of new cells, especially during the growth period. Carbohydrates are also part of nucleic acids.

Carbohydrates are also important in metabolism in the central nervous system. With a sharp decrease in the amount of sugar in the blood, severe disturbances in the activity of the nervous system are observed. Convulsions, delirium, loss of consciousness, and changes in heart activity occur. If such a person is given glucose into the blood or given regular sugar to eat, then after a while these severe symptoms disappear.

Sugar does not completely disappear from the blood even if it is absent from food, since carbohydrates in the body can be formed from proteins and fats.

The glucose requirement of different organs is not the same. The brain retains up to 12% of the supplied glucose, the intestines - 9%, the muscles - 7%, the kidneys - 5%. The spleen and lungs almost do not retain it at all.

Metabolism of carbohydrates in children. In children, carbohydrate metabolism occurs with great intensity, which is explained by the high level of metabolism in the children's body. Carbohydrates in a child’s body not only serve as the main source of energy, but also play an important plastic role in the formation of cell membranes and connective tissue substances. Carbohydrates also participate in the oxidation of acidic products of protein and fat metabolism, which helps maintain acid-base balance in the body.

The intensive growth of a child's body requires significant amounts of plastic material - proteins and fats, therefore the formation of carbohydrates in children from proteins and fats is limited. The daily requirement for carbohydrates in children is high and in infancy is 10-12 g per 1 kg of body weight. In subsequent years, the required amount of carbohydrates ranges from 8-9 to 12-15 g per 1 kg of body weight. A child aged 1 to 3 years should be given an average of 193 g of carbohydrates per day with food, from 4 to 7 years - 287 g, from 9 to 13 years - 370 g, from 14 to 17 years - 470 g, for an adult - 500 G.

Carbohydrates are absorbed by the child's body better than by adults (in infants - by 98-99%). In general, children are relatively more tolerant of high blood sugar levels than adults. In adults, glucose appears in the urine if it is 2.5-3 g per 1 kg of body weight, and in children this occurs only when 8-12 g of glucose per 1 kg of body weight is received. Taking small amounts of carbohydrates with food can cause children to double their blood sugar, but after 1 hour the blood sugar level begins to decrease and after 2 hours it is completely normalized.

Water and mineral metabolism. Vitamins. The importance of water and mineral salts. All transformations of substances in the body take place in an aquatic environment. Water dissolves nutrients that enter the body and transports dissolved substances. Together with minerals, it takes part in the construction of cells and in many metabolic reactions. Water is involved in the regulation of body temperature: by evaporating, it cools the body, protecting it from overheating.

Water and mineral salts create mainly the internal environment of the body, being the main component of blood plasma, lymph and tissue fluid. Some salts dissolved in the liquid part of the blood are involved in the transfer of gases in the blood.

Water and mineral salts are part of digestive juices, which determines their importance for digestive processes. And although neither water nor mineral salts are sources of energy in the body, their normal intake and removal from the body is a condition for its normal functioning. Water in an adult makes up approximately 65% of body weight, in children - about 80%.

Loss of water by the body leads to very serious disorders. For example, in case of indigestion in infants, dehydration poses a great danger; this entails convulsions and loss of consciousness. Depriving a person of water for several days is fatal.

Water exchange. The body is constantly replenished with water by absorbing it from the digestive tract. A person needs 2-2.5 liters of water per day with a normal diet and normal ambient temperature. This amount of water comes from the following sources: water consumed when drinking (about 1 l); water contained in food (about 1 l); water, which is formed in the body during the metabolism of proteins, fats and carbohydrates (300-350 cubic cm).

The main organs that remove water from the body are the kidneys, sweat glands, lungs and intestines. The kidneys remove 1.2-1.5 liters of water in urine from the body per day. The sweat glands remove 500-700 cubic meters through the skin in the form of sweat. cm of water per day. At normal temperature and air humidity per 1 sq. cm of skin, about 1 mg of water is released every 10 minutes. The lungs remove 350 cubic meters of water vapor. cm of water; this amount increases sharply with deepening and quickening of breathing, and then 700-800 cubic meters can be released per day. cm of water. 100-150 cubic meters are excreted through the intestines with feces per day. cm of water; when intestinal activity is disrupted, more water may be excreted, which leads to depletion of the body in water.

For normal functioning of the body, it is important that the intake of water into the body completely covers its consumption. If more water is removed from the body than enters it, a feeling of thirst occurs. The ratio of the amount of water consumed to the amount released is the water balance.

In a child’s body, extracellular water predominates, this causes greater hydrolability of children, i.e. the ability to quickly lose and quickly accumulate water. The need for water per 1 kg of body weight decreases with age, and its absolute amount increases. A three-month-old child needs 150-170 g of water per 1 kg of weight, at 2 years old - 95 g, at 12-13 years old - 45 g. The daily need for water for a one-year-old child is 800 ml, at 4 years old - 950-1000 ml, at 5 -6 years old - 1200 ml, at 7-10 years old - 1350 ml, at 11-14 years old - 1500 ml.

The importance of mineral salts in the process of child growth and development. The presence of minerals is associated with the phenomenon of excitability and conductivity in the nervous system. Mineral salts provide a number of vital functions of the body, such as the growth and development of bones, nerve elements, muscles; determine the blood reaction (pH), contribute to the normal functioning of the heart and nervous system; used for the formation of hemoglobin (iron), hydrochloric acid of gastric juice (chlorine); maintain a certain osmotic pressure.

In a newborn, minerals make up 2.55% of body weight, in an adult - 5%. With a mixed diet, an adult receives all the minerals he needs in sufficient quantities from food, and only table salt is added to human food during cooking. A growing child's body especially needs an additional supply of many minerals.

Minerals have an important impact on child development. Calcium and phosphorus metabolism are associated with bone growth, the timing of cartilage ossification and the state of oxidative processes in the body. Calcium affects the excitability of the nervous system, muscle contractility, blood clotting, protein and fat metabolism in the body. Phosphorus is needed not only for the growth of bone tissue, but also for the normal functioning of the nervous system, most glandular and other organs. Iron is part of blood hemoglobin.

The greatest need for calcium is observed in the first year of a child’s life; at this age it is eight times more than in the second year of life, and 13 times more than in the third year; then the need for calcium decreases, increasing slightly during puberty. For schoolchildren, the daily need for calcium is 0.68-2.36 g, for phosphorus - 1.5-4.0 g. The optimal ratio between the concentration of calcium and phosphorus salts for preschool children is 1: 1, at the age of 8-10 years - 1: 1.5, in adolescents and older schoolchildren - 1: 2. With such ratios, skeletal development proceeds normally. Milk contains an ideal ratio of calcium and phosphorus salts, so the inclusion of milk in children's diet is mandatory.

The need for iron in children is higher than in adults: 1-1.2 mg per 1 kg of body weight per day (in adults - 0.9 mg). Children should receive sodium 25-40 mg per day, potassium - 12-30 mg, chlorine - 12-15 mg.

Vitamins. These are organic compounds that are absolutely necessary for the normal functioning of the body. Vitamins are part of many enzymes, which explains the important role of vitamins in metabolism. Vitamins contribute to the action of hormones, increasing the body's resistance to adverse environmental influences (infections, high and low temperatures, etc.). They are necessary to stimulate growth, tissue and cell restoration after injury and surgery.

Unlike enzymes and hormones, most vitamins are not produced in the human body. Their main sources are vegetables, fruits and berries. Vitamins are also contained in milk, meat, and fish. Vitamins are required in very small quantities, but their deficiency or absence in food disrupts the formation of the corresponding enzymes, which leads to diseases - vitamin deficiencies.

All vitamins are divided into two large groups: a) water-soluble; b) soluble in fats. Water-soluble vitamins include the group of vitamins B, vitamins C and P. Fat-soluble vitamins include vitamins A1 and A2, D, E, K.

Vitamin B1 (thiamine, aneurin) is found in hazelnuts, brown rice, wholemeal bread, barley and oatmeal, especially in brewer's yeast and liver. The daily requirement for the vitamin is 1 mg in children under 7 years old, 1.5 mg from 7 to 14 years old, 2 mg from 14 years old, and 2-3 mg in adults.

Without vitamin B1 in food, beriberi disease develops. The patient loses his appetite, quickly gets tired, and weakness gradually appears in the leg muscles. Then there is a loss of sensitivity in the leg muscles, damage to the auditory and optic nerves, cells of the medulla oblongata and spinal cord die, paralysis of the limbs occurs, and without timely treatment - death.

Vitamin B2 (riboflavin). In humans, the first sign of a lack of this vitamin is skin lesions (most often in the lip area). Cracks appear, become wet and become covered with a dark crust. Later, damage to the eyes and skin develops, accompanied by the falling off of keratinized scales. In the future, malignant anemia, damage to the nervous system, a sudden drop in blood pressure, convulsions, and loss of consciousness may develop.

Vitamin B2 is found in bread, buckwheat, milk, eggs, liver, meat, and tomatoes. The daily need for it is 2-4 mg.

Vitamin PP (nicotinamide) is found in green vegetables, carrots, potatoes, peas, yeast, buckwheat, rye and wheat bread, milk, meat, and liver. The daily need for it in children is 15 mg, in adults - 15-25 mg.

With vitamin deficiency RR, a burning sensation in the mouth, excessive salivation and diarrhea are noted. The tongue becomes crimson-red. Red spots appear on the arms, neck, and face. The skin becomes rough and rough, which is why the disease is called pellagra (from Italian pelle agra - rough skin). In severe cases of the disease, memory weakens, psychosis and hallucinations develop.

Vitamin B12 (cyanocobalamin) in humans is synthesized in the intestines. Contained in the kidneys, liver of mammals and fish. With its deficiency, the body develops malignant anemia associated with impaired formation of red blood cells.

Vitamin C (ascorbic acid) is widely distributed in nature in vegetables, fruits, pine needles, and liver. Ascorbic acid is well preserved in sauerkraut. 100 g of pine needles contain 250 mg of vitamin C, 100 g of rose hips - 150 mg. The requirement for vitamin C is 50-100 mg per day.

Lack of vitamin C causes scurvy. Usually the disease begins with general malaise and depression. The skin takes on a dirty gray tint, gums bleed, and teeth fall out. Dark spots of hemorrhage appear on the body, some of them ulcerate and cause sharp pain.

Vitamin A (retinol, axerophthol) in the human body is formed from the common natural pigment carotene, found in large quantities in fresh carrots, tomatoes, lettuce, apricots, fish oil, butter, liver, kidneys, and egg yolk. The daily requirement for vitamin A for children is 1 mg, for adults - 2 mg.

With a lack of vitamin A, the growth of children slows down and “night blindness” develops, i.e. a sharp drop in visual acuity in dim lighting, leading in severe cases to complete but reversible blindness.

Vitamin D (ergocalciferol) is especially necessary for children to prevent one of the most common childhood diseases - rickets. With rickets, the process of bone formation is disrupted, the bones of the skull become soft and pliable, and the limbs become bent. Hypertrophied parietal and frontal tubercles form on softened areas of the skull. Lethargic, pale, with an unnaturally large head and a short bow-legged body, a large belly, such children are sharply retarded in development.

All these severe disorders are associated with the absence or deficiency of vitamin D in the body, which is found in yolks, cow's milk, and fish oil.

Vitamin D can be formed in human skin from the provitamin ergosterol under the influence of ultraviolet rays. Fish oil, sun exposure or artificial ultraviolet irradiation are means of preventing and treating rickets.

4. Age-related characteristics of energy metabolism

metabolism biological food carbohydrate

Even in conditions of complete rest, a person spends a certain amount of energy: the body continuously spends energy on physiological processes that do not stop for a minute. The minimum level of metabolism and energy expenditure for the body is called the basal metabolism. Basal metabolism is determined in a person in a state of muscular rest - lying down, on an empty stomach, i.e. 12-16 hours after eating, at an ambient temperature of 18-20 ° C (comfort temperature). In a middle-aged person, the basal metabolism is 4187 J per 1 kg of weight per hour. On average, this is 7,140,000-7,560,000 J per day. For each person, the basal metabolic rate is relatively constant.

Features of basal metabolism in children. Since children have a relatively larger body surface per unit mass than an adult, their basal metabolism is more intense than that of adults. In children there is also a significant predominance of assimilation processes over dissimilation processes. The younger the child, the higher the energy costs for growth. Thus, energy consumption associated with growth at the age of 3 months is 36%, at the age of 6 months - 26%, 9 months - 21% of the total energy value of food.

The basal metabolism per 1 kg of weight in an adult is 96,600 J. Thus, in children 8-10 years old, the basal metabolism is two or two and a half times higher than in adults.

The basal metabolic rate in girls is slightly lower than in boys. This difference begins to appear already in the second half of the first year of life. The work performed by boys entails higher energy consumption than by girls.

Determining the basal metabolic rate often has diagnostic value. The basal metabolism increases with excessive thyroid function and some other diseases. If the function of the thyroid gland, pituitary gland, or gonads is insufficient, the basal metabolism decreases.

Energy expenditure during muscle activity. The harder the muscular work, the more energy a person spends. For schoolchildren, preparing for a lesson and a lesson at school require energy 20-50% higher than the basal metabolic energy.

When walking, energy expenditure is 150-170% higher than the basal metabolism. When running or climbing stairs, energy costs exceed the basal metabolism by 3-4 times.

Training the body significantly reduces energy consumption for the work performed. This is due to a decrease in the number of muscles involved in work, as well as changes in breathing and blood circulation.

People of different professions have different energy expenditures. During mental work, energy costs are lower than during physical work. Boys have a higher total daily energy expenditure than girls.

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Plan.

Lecture 17

Topic: “Age-related features of metabolism”

12. Metabolism and energy, its age-related characteristics.

13. Nutrients, their composition, energy value, nutritional standards.

14. Prevention of gastrointestinal diseases.

Metabolism refers to the set of changes that substances undergo from the moment they enter the digestive tract to the formation of final breakdown products excreted from the body. That is, metabolism in all organisms, from the most primitive to the most complex, including the human body, is the basis of life.

In the process of life, continuous changes occur in the body: some cells die, others replace them. In an adult, 1/20 of the skin epithelial cells and half of all epithelial cells of the digestive tract, about 25 g of blood, etc. die and are replaced within 24 hours.

During the process of growth, renewal of the body's cells is possible only when the body continuously receives oxygen and nutrients, which are the building materials from which the body is built. But for the construction of new cells of the body, their continuous renewal, as well as for a person to perform some kind of work, energy is needed. The human body receives this energy through decay and oxidation in metabolic processes (metabolism). Moreover, metabolic processes (anabolism and catabolism) are finely coordinated with each other and occur in a certain sequence.

Under anabolism understand the set of synthesis reactions. Under catabolism- a set of decomposition reactions. It must be taken into account that both of these processes are continuously connected. Catabolic processes provide anabolism with energy and starting substances, and anabolic processes provide the synthesis of structures, the formation of new tissues in connection with the growth processes of the body, the synthesis of hormones and enzymes necessary for life.

Throughout individual development, the most significant changes are experienced by the anabolic phase of metabolism and, to a lesser extent, by the catabolic phase.

According to their functional significance in the anabolic phase of metabolism, the following types of synthesis are distinguished:

1) growth synthesis - an increase in the protein mass of organs during a period of increased cell division, growth of the organism as a whole.

2) functional and protective synthesis - the formation of proteins for other organs and systems, for example, the synthesis of blood plasma proteins in the liver, the formation of digestive tract enzymes and hormones.

3) synthesis of regeneration (recovery) - synthesis of proteins in regenerating tissues after injury or malnutrition.

4) synthesis of self-renewal associated with stabilization of the body - constant replenishment of components of the internal environment that are destroyed during dissimilation.

All these forms weaken, although unevenly, throughout individual development. In this case, especially significant changes are observed in growth synthesis. The intrauterine period has the highest growth rates. For example, the weight of a human embryo increases by 1 billion compared to the weight of a zygote. 20 million times, and over 20 years of progressive human growth it increases no more than 20 times.

Throughout postnatal life, there is a further decline in the level of anabolism.

Protein metabolism in a developing organism. Growth processes, the quantitative indicators of which are an increase in body weight and the level of positive nitrogen balance, are one side of development. Its second side is the differentiation of cells and tissues, the biochemical basis of which is the synthesis of enzymatic, structural and functional proteins.

Proteins are synthesized from amino acids that come from the digestive system. Moreover, these amino acids are divided into essential and non-essential. If essential amino acids (leucine, methionine and tryptophan, etc.) are not supplied with food, then protein synthesis in the body is disrupted. The supply of essential amino acids is especially important for a growing organism, for example, the lack of lysine in food leads to growth retardation, depletion of the muscular system, and a lack of valine leads to balance disorders in a child.

In the absence of essential amino acids in food, they can be synthesized from essential ones (tyrosine can be synthesized from phenylalanine).

And finally, proteins that contain the entire necessary set of amino acids that ensure normal synthesis processes are classified as biologically complete proteins. The biological value of the same protein varies for different people depending on the state of the body, diet, and age.

The daily protein requirement per 1 kg of weight in a child: at 1 year - 4.8 g, 1-3 years - 4-4.5 g; 6-10 years - 2.5-3 g, 12 and more - 2.5 g, adults - 1.5-1.8 g. Therefore, depending on age, children under 4 years old should receive 50 g of protein, up to 7 years - 70 g, from 7 years - 80 g per day.

The amount of proteins entering the body and destroyed in it is judged by the value of the nitrogen balance, that is, the ratio of the amounts of nitrogen that enters the body with food and is excreted from the body with urine, sweat and other secretions.

The ability to retain nitrogen in children is subject to significant individual fluctuations and persists throughout the entire period of progressive growth.

As a rule, adults do not have the ability to retain dietary nitrogen; their metabolism is in a state of nitrogen equilibrium. This indicates that the potential for protein synthesis remains for a long time - thus, under the influence of physical activity, muscle mass increases (positive nitrogen balance).

During periods of stable and regressive development, upon reaching maximum weight and cessation of growth, the main role begins to be played by the processes of self-renewal, which occur throughout life and which fade into old age much more slowly than other types of synthesis.

Age-related changes affect not only protein, but also fat and carbohydrate metabolism.

Age-related dynamics of fat and carbohydrate metabolism.

The physiological role of lipids - fats, phosphatides and sterols in the body is that they are part of cellular structures (plastic metabolism), and are also used as rich sources of energy (energy metabolism). Carbohydrates in the body are important as energy material.

With age, fat and carbohydrate metabolism changes. Fats play a significant role in the processes of growth and differentiation. Fat-like substances are especially important, primarily because they are necessary for the morphological and functional maturation of the nervous system, for the formation of all types of cell membranes. That is why the need for them in childhood is great. With a lack of carbohydrates in food, fat depots in children are quickly depleted. The intensity of synthesis largely depends on the nature of the diet.

The phases of stable and regressive development are characterized by a peculiar reorientation of anabolic processes: a switch of anabolism from protein synthesis to fat synthesis, which is one of the characteristic features of age-related changes in metabolism during aging.

The age-related reorientation of anabolism towards fat accumulation in a number of organs is based on a decrease in the ability of tissues to oxidize fat, as a result of which, with a constant and even reduced rate of fatty acid synthesis, the body is enriched with fats (thus, the development of obesity was observed even with 1-2 meals a day). It is also undeniable that in the reorientation of synthesis processes, in addition to nutritional factors and nervous regulation, changes in the hormonal spectrum are of great importance, in particular changes in the rate of formation of somatotropic hormone, thyroid hormones, insulin, and steroid hormones.

Restructures with age and carbohydrate metabolism. In children, carbohydrate metabolism occurs with greater intensity, which is explained by a high metabolic rate. In childhood, carbohydrates perform not only an energy function, but also a plastic function, forming cell membranes and connective tissue substances. Carbohydrates participate in the oxidation of protein and fat metabolism products, which helps maintain acid-base balance in the body. The daily requirement for carbohydrates in children is high and in infancy is 10-12 g per 1 kg of body weight. In subsequent years, at the age of 8-9 years, it increases to 12-15 g per 1 kg of body weight. From 1 to 3 years, a child needs to receive about 193 g of carbohydrates per day from food, 4-7 years - 287, 9-13 - 370, 14-17 years - 470, and adults - 500 g.

Carbohydrates are absorbed better by children's bodies than by adults. One of the significant indicators of age-related changes in carbohydrate metabolism is a sharp increase in old age in the time it takes to eliminate hyperglycemia caused by the administration of glucose during sugar load tests.

An important part of metabolism in the body is water-salt metabolism.

The transformation of substances in the body takes place in an aquatic environment; together with minerals, water takes part in the construction of cells and serves as a reagent in cellular chemical reactions. The concentration of mineral salts dissolved in water determines the osmotic pressure of blood and tissue fluid, thus being of great importance for absorption and excretion. changes in the amount of water in the body and shifts in the salt composition of body fluids and tissue structures entail a violation of the stability of colloids, which can result in irreversible damage and death of individual cells and then the body as a whole. That is why maintaining a constant amount of water and mineral composition is a necessary condition for normal life.

In the progressive growth phase, water participates in the processes of creating body weight. It is known, for example, that out of a daily increase in body weight of 25 g, water accounts for 18, protein - 3, fat - 3 and mineral salts - 1 g. The younger the body, the greater the daily need for water. In the first six months of life, a child’s need for water reaches 110-125 g per 1 kg of weight, by 2 years it decreases to 115-136 g, at 6 years - 90-100 g, 18 years - 40-50 g. Children are able to quickly lose and also quickly deposit water.

A general pattern of individual evolution is a decrease in water in all tissues. With age, a redistribution of water in tissues occurs - the volume of water in the intercellular spaces increases and the volume of intracellular water decreases.

The balance of many mineral salts depends on age. In youth, the content of most inorganic salts is lower than in adults. The exchange of calcium and phosphorus is of particular importance. Increased requirements for the supply of these elements in children under one year of age are explained by increased formation of bone tissue. But these elements are no less important in old age. Therefore, older people need to introduce foods containing these elements (milk, dairy products) into their diet to avoid wasting these elements from bone tissue. The content of sodium chloride, on the contrary, should be reduced in the diet due to the weakening of the production of mineralocorticoids in the adrenal glands with age.

An important indicator of energy transformations in the body is o main exchange.

Age dynamics of basal metabolism

The basal metabolic rate is understood as the minimum level of metabolism and energy expenditure for the body under strictly constant conditions: 14-16 hours before a meal, in a lying position in a state of muscular rest at a temperature of 8-20 C. In a middle-aged person, the basal metabolic rate is 4187 J per 1 kg of mass per 1 hour. On average, this is 7-7.6 MJ per day. Moreover, for each person the basal metabolic rate is relatively constant.

The basal metabolism in children is more intense than in adults, since they have a relatively large body surface per unit of mass, and the processes of dissimilation rather than assimilation are predominant. The younger the child, the higher the energy costs for growth. So the energy expenditure associated with growth at 3 months of age is 36%, at 6 months of age. - 26%, 9 months. - 21% of the total energy value of food.

In old age (the phase of regressive development), a decrease in body weight is observed, as well as a decrease in the linear dimensions of the human body, and the basal metabolism drops to low values. Moreover, the degree of decrease in basal metabolism at this age correlates, according to various researchers, with the extent to which signs of frailty and loss of performance are expressed in old people.

As for gender differences in the level of basal metabolism, they are detected in ontogenesis from 6-8 months. At the same time, the basal metabolic rate in boys is higher than in girls. Such relationships persist during puberty, and in old age they smooth out.

In ontogenesis, not only the average value of energy metabolism varies, but also the possibilities of increasing this level under conditions of intense, for example, muscle activity, change significantly.

In early childhood, insufficient functional maturity of the musculoskeletal, cardiovascular and respiratory systems limits the adaptive capabilities of the energy metabolism reaction during physical activity. In adulthood, adaptive capacity, as well as muscle strength, reach their maximum. In old age, the possibilities for a compensatory increase in the level of respiration and energy exchange under stress are exhausted due to a decrease in the vital capacity of the lungs, the coefficient of oxygen utilization by tissues, and a decrease in the functions of the cardiovascular system.

Various assumptions have been made and various mathematical expressions have been proposed to establish the dependence of energy production on parameters characterizing the structural features of the organism. Thus, Rubner believed that age-related changes in metabolism are the result of a decrease in the size of the relative surface of the body with age.

An attempt was made to explain the decline in metabolic processes in old age by the accumulation of subcutaneous fat and a decrease in skin temperature at this age.

Noteworthy are the works in which changes in energy metabolism are considered in connection with the formation of thermoregulation mechanisms and the participation of skeletal muscles in it (Magnus, 1899; Arshavsky, 1966-71).

An increase in skeletal muscle tone with insufficient activity of the vagus nerve center during the first year of life helps to increase energy metabolism. The role of age-related restructuring of skeletal muscle activity in the dynamics of energy metabolism is especially clearly highlighted in the study of gas exchange in people of different ages at rest and during physical activity. For progressive growth, an increase in resting metabolism is characterized by a decrease in the level of basal metabolism and improved energy adaptation to muscle activity. During the stable phase, a high functional rest metabolism is maintained and the metabolism during work increases significantly, reaching a stable, minimum level of basal metabolism. And in the regressive phase, the difference between the functional rest metabolism and the basal metabolism continuously decreases, and the rest time lengthens.

Many researchers believe that the decrease in the energy metabolism of the whole organism during ontogenesis is due, first of all, to quantitative and qualitative changes in metabolism in the tissues themselves, the magnitude of which is judged by the relationship between the main mechanisms of energy release - anaerobic and aerobic. This makes it possible to determine the potential capabilities of tissues to generate and use the energy of high-energy bonds.

Metabolism call a complex complex of various interdependent and interdependent processes that occur in the body from the moment these substances enter it until the moment they are released. Metabolism is a necessary condition for life. It constitutes one of its obligatory manifestations.

For the normal functioning of the body, it is necessary to receive organic food material, mineral salts, water and oxygen from the external environment. Over a period equal to the average life expectancy of a person, he consumes 1.3 tons of fats, 2.5 tons of proteins, 12.5 tons of carbohydrates and 75 tons of water.

Main stages

Metabolism consists of the processes of substances entering the body, their changes in the digestive tract, absorption, transformations within cells and the removal of their breakdown products. Processes associated with the transformation of substances inside cells are called intracellular or intermediate metabolism.

As a result of intracellular metabolism, hormones, enzymes and a variety of compounds are synthesized, used as structural material for the construction of cells and intercellular substance, which ensures the renewal and growth of the developing organism.

The processes that result in the formation of living matter are called anabolism or assimilation.

The other side of metabolism is that the substances that form a living structure undergo breakdown. This process of destruction of living matter is called catabolism or dissimilation. The processes of assimilation and dissimilation are very closely related, although they are opposite in their final results. Thus, it is known that the breakdown products of various substances contribute to their enhanced synthesis.

Oxidation of breakdown products serves as a source of energy, which the body constantly spends even in a state of complete rest. In this case, the same substances that are used for the synthesis of larger molecules can undergo oxidation. For example, in the liver, glycogen is synthesized from part of the carbohydrate breakdown products, and the energy for this synthesis is provided by another part of them, which is included in metabolic or metabolic processes. The processes of assimilation and dissimilation occur with the obligatory participation of enzymes.

At different age periods, the nature of metabolism changes. During the period of growth and development, it is characterized by the greatest intensity, which ensures plastic and structural processes. The protein requirement during growth per unit of body weight is significantly greater than in adults.

The basal metabolic rate in children is 1.5-2 times higher than the basal metabolic rate of an adult. The relative value of basal metabolism (in kilocalories per 1 kg of body weight) decreases with age: in children 2-3 years old - 55, 6-7 years old - 42, 10-11 years old - 33, 12-13 years old - 34, in adults - 24.

Childhood and adolescence are characterized by relatively high energy expenditure. The average energy expenditure of an adult is 45 kcal per 1 kg of body weight, for children aged 1-5 years - 80-100 kcal, for adolescents 13-16 years old - 50-65 kcal.

Increased basal metabolism and energy expenditure in children and adolescents dictate the need for a special approach to organizing their nutrition.

Thus, in school and adolescence, when energy expenditure on various types of activity increases significantly, it is necessary to take into account that their provision in the daily diet should come from proteins (about 14%), fats (about 31%) and carbohydrates (about 55%) . Ensuring the body's plastic processes and energy functions is most fully achieved with a balanced diet.

Nutrition

The concept of a balanced diet is based on determining the absolute amount of each of the nutritional factors and their ratio, taking into account the physiological characteristics of a particular age.

Imbalance of the main components of nutrition adversely affects metabolic processes, negatively affecting growth. This is especially evident when there is a violation of the ratio of protein and fat components in the diet.

The rational ratio of proteins and fats in children's nutrition is 1:1. The approximate content of fats, fats and carbohydrates in food is 1:1:3 for young children and 1:1:4 for older children. 270 Chapter b

During the period of growth and development, the plastic function of mineral elements, which are an integral part of the cells and tissues of the body, as well as biocatalysts of metabolic processes, is important. Calcium, which is a structural element of bone tissue, deserves special attention. It has been established that the metabolism and absorption of calcium in the body depends on the content of phosphorus and magnesium. With an excess of these elements, the formation of digestible forms of calcium is limited, and it is excreted from the body. The optimal ratio of calcium and phosphorus in foods for infants for absorption by the body is 1.2:1, from 1 year to 3 years - 1:1, over 4 years - 1:1.2 or 1:1.5. The optimal ratio of calcium and magnesium is 1:0.7.

Children's nutrition has a number of differences from the diet of adults. During childhood, especially in young children, the need for nutrients and energy is relatively higher than in adults. This is explained by the predominance of assimilation over desimilation, associated with the rapid pace of growth and development of the child. The scientific substantiation of the norms for the nutritional needs of children of different age groups and the substantiation of the sets of products necessary to cover these needs was carried out on the basis of the development of the child’s body. The values of the physiological needs of children of different age groups for nutrients are established taking into account the functional and anatomical and morphological characteristics inherent in each age group. The recommended nutritional requirements for children are designed to avoid, as far as possible, both malnutrition in children and the introduction of excess nutrients into their bodies.

Deviation from these principles has a negative impact on the development of children. A number of pathological conditions associated with poor nutrition in children at an early age. These include: impaired tooth formation, caries, the risk of diabetes, hypertension syndrome, renal pathology, allergic diseases, obesity.

Food is the only source from which a child receives the necessary plastic material and energy. But a child’s body differs from an adult precisely in that the processes of growth and development rapidly occur within it.

The body of children and adolescents has a number of other significant features. Children's body tissues consist of 25% proteins, fats, carbohydrates, mineral salts and 75% water. The basal metabolism in children proceeds 1.5-2 times faster than in an adult. In the body of children and adolescents, due to their growth and development, the process of assimilation prevails over dissimilation. Due to increased muscle activity, their total energy costs are increased. The average energy consumption per day (kcal) per 1 kg of body weight for children of various ages and an adult is:

As a result of mastering this chapter, the student should: know

stages of metabolism and energy: anabolism and catabolism;
characteristics of general and basal metabolism;
specific dynamic effect of food;
methods for assessing the body's energy expenditure;
age-related metabolic features; be able to
explain the importance of metabolism for the human body;
connect age-related metabolic characteristics with energy consumption at different age periods;

own

Knowledge of the participation of nutrients in metabolism.

Characteristics of metabolism in the body

Metabolism, or metabolism(from Greek metabole - transformation) is a set of chemical and physical transformations that occur in a living organism and ensure its vital activity in conjunction with the external environment. In the metabolism and energy, there are two opposing interconnected processes: anabolism, which underlies assimilation, and catabolism, the basis of which is dissimilation.

Anabolism(from Greek anabole - rise) - a set of processes of synthesis of tissue and cellular structures, as well as compounds necessary for the life of the body. Anabolism ensures growth, development and renewal of biological structures, accumulation of energy substrate. Energy is stored in the form of high-energy phosphate compounds (macroergs), such as ATP.

Catabolism(from Greek katabole - throwing down) - a set of processes of disintegration of tissue and cellular structures and the breakdown of complex compounds for the energetic and plastic support of life processes. During catabolism, chemical energy is released, which is used by the body to maintain the structure and function of the cell, as well as to ensure specific cellular activities: muscle contraction, secretion of glandular secretions, etc. The end products of catabolism - water, carbon dioxide, ammonia, urea, uric acid, etc. - are removed from the body.

Thus, catabolic processes supply energy and starting materials for anabolism. Anabolic processes are necessary for the construction and restoration of structures and cells, the formation of tissues during growth, for the synthesis of hormones, enzymes and other compounds necessary for the functioning of the body. For catabolic reactions they supply macromolecules to be broken down. The processes of anabolism and catabolism are interconnected and are in the body in a state dynamic balance. The state of equilibrium or nonequilibrium ratio of anabolism and catabolism depends on age, state of health, physical or mental stress. In children, the predominance of anabolic processes over catabolic ones characterizes the processes of growth and accumulation of tissue mass. The most intense increase in body weight is observed in the first three months of life - 30 g/day. By the year it decreases to 10 g/day, in subsequent years the decrease continues. The energy cost of growth is also greatest in the first three months and amounts to about 140 kcal/day or 36% of the energy value of food. From three years to puberty, it decreases to 30 kcal/day, and then increases again - to 110 kcal/day. Anabolic processes are more intense in adults during the recovery period after illness. The predominance of catabolic processes is typical for people who are old or exhausted by a severe long-term illness. As a rule, this is associated with the gradual destruction of tissue structures and the release of energy.

The essence of metabolism is the entry into the body of various nutrients from the external environment, their assimilation and use as sources of energy and material for building the structures of the body and the release of metabolic products formed in the process of vital activity into the external environment. In this regard, they highlight four main components of the exchange function."

extracting energy from the environment in the form of chemical energy of organic substances;
the transformation of nutrients coming from food into simpler substances, from which macromolecules that make up the components of cells are formed;
assembly of proteins, nucleic acids and other cellular components from these substances;
synthesis and destruction of molecules necessary to perform various specific functions of the body.

Metabolism in the body occurs in several stages. First stage - transformation of nutrients in the digestive tract. Here, complex substances are broken down into simpler ones - glucose, amino acids and fatty acids, which can be absorbed into the blood or lymph. When nutrients are broken down in the gastrointestinal tract, energy is released, which is called primary heat. It is used by the body to maintain temperature homeostasis.

Second phase transformation of substances takes place inside the cells of the body. This is the so-called intracellular, or intermediate, exchange. Inside the cell, the products of the first stage of metabolism - glucose, fatty acids, glycerol, amino acids - are oxidized and phosphorylated. These processes are accompanied by the release of energy, most of which is stored in high-energy ATP bonds. The reaction products provide the cell with the building blocks for the synthesis of a variety of molecular components. Numerous enzymes play a decisive role in this process. With their participation, complex chemical reactions of oxidation and reduction, phosphorylation, transamination, etc. are carried out inside the cell. Metabolism in the cell is possible only with the integration of all complex biochemical transformations of proteins, fats and carbohydrates with the participation of their common energy sources (ATP) and due to the existence common precursors or common intermediates. The total energy reserve of the cell is formed due to the reaction of biological oxidation.

Biological oxidation can be aerobic or anaerobic. Aerobic(from lat. aeg - air) processes require the presence of oxygen, are carried out in mitochondria and are accompanied by the accumulation of a large amount of energy, covering the main energy expenditure of the body. Anaerobic processes occur without the participation of oxygen, mainly in the cytoplasm and are accompanied by the accumulation of a small amount of energy in the form of ATP, used to satisfy the limited short-term needs of the cell. Thus, the muscle tissue of an adult is characterized by aerobic processes, while anaerobic processes predominate in the energy metabolism of the fetus and children in the first days of life.

With complete oxidation of 1 M glucose or amino acids, 25.5 M ATP is formed, and with complete oxidation of fats, 91.8 M ATP is formed. The energy stored in ATP is used by the body to perform useful work and is converted into secondary heat. Thus, the energy released by the oxidation of nutrients in the cell is ultimately converted into thermal energy. As a result of aerobic oxidation, nutrient products are converted into C0 2 and H 2 0, which are harmless to the body.

However, a direct combination of oxygen with oxidizable substances without the participation of enzymes, called free radical oxidation, can also occur in the cell. This produces free radicals and peroxides that are highly toxic to the body. They damage cell membranes and destroy structural proteins. Prevention of this type of oxidation is the consumption of vitamins E, A, C, etc., as well as microelements (Se, etc.), which convert free radicals into stable molecules and prevent the formation of toxic peroxides. This ensures the normal course of biological oxidation in the cell.

Final stage metabolism - the release of breakdown products with urine and excreta of the sweat and sebaceous glands.

Plastic and energy metabolism act as a single whole in the body, but the role of various nutrients in their implementation is different. In an adult, the products of the breakdown of fats and carbohydrates are mainly used to provide energy processes, and proteins are used to build and restore cell structures. In children, due to the intensive growth and development of the body, carbohydrates participate in plastic processes. Biological oxidation serves as a source not only of energy-rich phosphates, but also of carbon compounds used in the biosynthesis of amino acids, carbohydrates, lipids and other cell components. This explains the significantly higher intensity of energy metabolism in children.

All the energy of the chemical bonds of nutrients entering the body is ultimately converted into heat (primary and secondary heat), therefore, by the amount of heat generated, one can judge the amount of energy required to carry out life activities.

To assess the body's energy expenditure, direct and indirect calorimetry methods are used, with which one can determine the amount of heat generated by the human body. Direct calorimetry is based on measuring the amount of heat that the body releases into the environment (for example, per hour or per day). For this purpose, a person is placed in a special cell - calorimeter(Fig. 12.1). The walls of the calorimeter are washed by water, the heating temperature of which is used to determine the amount of energy released. Direct calorimetry provides high accuracy in assessing the body's energy expenditure, but due to its bulkiness and complexity, this method is used only for special purposes.

To determine a person’s energy expenditure, a simpler and more accessible method is often used indirect calorimeter

Rice. 12.1.

The calorimeter is used for research carried out on humans. The total energy released consists of: 1) the resulting heat, measured by the increase in the temperature of the water flowing in the chamber coil; 2) latent heat of vaporization, measured by the amount of water vapor extracted from the surrounding air by the first absorber H 2 0; 3) work aimed at objects located outside the camera. Consumption of 0 2 is measured by the amount that has to be added so that its content in the chamber remains constant

rii - according to gas exchange data. Considering that the total amount of energy released by the body is the result of the breakdown of proteins, fats and carbohydrates, and also knowing the amount of energy released during the breakdown of each of these substances (their energy value), and the amount of decayed substances over a certain period of time, it is possible to calculate the amount released energy. To determine which substances have undergone oxidation in the body (proteins, fats or carbohydrates), calculate respiratory quotient(DC), which is understood as the ratio of the volume of carbon dioxide released to the volume of absorbed oxygen. The respiratory coefficient is different during the oxidation of proteins, fats and carbohydrates. If there is information about the volumes of absorbed oxygen and exhaled carbon dioxide, the indirect calorimetry method is called “full gas analysis”. To perform this, you need equipment that allows you to determine the volume of carbon dioxide. In classical bioenergy, a Douglas bag, a gas clock, and a Holden gas analyzer, which contains carbon dioxide and oxygen absorbers, are used for this purpose. The method allows you to estimate the percentage of 0 2 and C0 2 in the air sample under study. Based on the measurement data, the volume of absorbed oxygen and exhaled carbon dioxide is calculated.

Let us examine the essence of this method using the example of glucose oxidation. The total formula for the breakdown of carbohydrates is expressed by the equation

For fats, DC is 0.7. During the oxidation of protein and mixed foods, the DC value takes an intermediate value: between 1 and 0.7.

The subject takes the mouthpiece of the Douglas bag into his mouth (Fig. 12.2), his nose is closed with a clamp, and all the air exhaled over a certain period of time is collected in a rubber bag.

The volume of exhaled air is determined using a gas clock. An air sample is taken from the bag and the oxygen and carbon dioxide content in it is determined. The content of gases in the inhaled air is known. Based on the difference in percentage, the amount of oxygen consumed, carbon dioxide released and DC is calculated:

Knowing the value of DC, find the caloric equivalent of oxygen (CEO2) (Table 12.1), i.e. the amount of heat generated in the body when 1 liter of oxygen is consumed.

Rice. 12.2.

By multiplying the value of KE0 2 by the number of liters of consumed 0 2, the exchange value is obtained for the period of time during which gas exchange was determined.

It is used to determine the daily exchange rate.

Currently, there are automatic gas analyzers that allow you to simultaneously determine the volume of consumed 0 2 and the volume of exhaled CO 2 . However, most available medical devices can only determine the volume of absorbed 0 2 , so the method is widely used in practice indirect calorimetry, or incomplete gas analysis. In this case, only the volume of absorbed 0 2 is determined, so calculation of DC is impossible. It is conventionally accepted that carbohydrates, proteins, and fats are oxidized in the body. It is believed that DC in this case is equal to 0.85. It corresponds to EC0 2 equal to 4.862 kcal/l. Further calculations are carried out as with a full gas analysis.

Table 12.1

The value of DC and EC0 2 during the oxidation of various nutrients in the body

Many people notice that getting back into shape after the holidays becomes increasingly difficult as they age. There are also cases when extra pounds begin to appear as if out of thin air. Why is this happening?

Dr. Caroline Cederquist, author of The MD Factor Diet, believes that metabolic changes (while they vary from person to person) begin to appear around age 20, 30, 40 or 50 for some people. Therefore, it will be useful for every person to know how the body’s metabolic system works and how to optimize its functioning at any age.

Metabolic changes characteristic of the body at 20, 30, 40 and 50 years old

Below are the main metabolic changes that occur in the body approximately every ten years. It is worth understanding that the time marks taken as a basis are approximate and may vary depending on the person’s health and lifestyle.

Changes in metabolism manifest themselves in each person individually.

Metabolism between 20 and 30 years of age

On average, this is the age at which many people experience their highest resting metabolic rate, i.e. when we do nothing. This feature also depends on genetic factors, but the level of human activity plays a large role in this aspect.

It is also necessary to remember that until about 25 years of age, the process of intensive bone growth continues, so calories are burned quite intensively. Closer to the age of 30, many people notice that taking liberties with high-calorie foods leads to the appearance of unnecessary centimeters in problem areas. However, regular exercise and smart eating will help you get back into shape quite quickly.

Metabolism between 30 and 40 years of age

If by this time you have not started doing strength training, it’s time to start. Your resting metabolic rate is directly related to your muscle mass. The greater the muscle mass, the more energy the body will need to burn, including at rest. From about age 30, muscle mass begins to decrease at a rate of 1% per year. If you don't use your muscles, you can accept that fat will accumulate in your body. Strength training (2-3 times a week) will help prevent the consequences of this unpleasant process.

Decreased muscle mass and decreased production of growth hormone contribute to a slower metabolism.

Women generally find it difficult to maintain muscle mass. Testosterone levels in men are much higher than in women, so the percentage of body fat in men is much lower than in women. And muscle mass in men is correspondingly greater.

Another age-related feature is a decrease in the production of growth hormone at about 30 years of age. As a result, there is a change in metabolism towards its slowdown. Strength training will help increase the amount of growth hormone produced.

Metabolism between 40 and 50 years of age

Surveys have shown that, on average, up to the age of 40, women manage to stay on diets for 6 years, but within 5 years, 95% of women who lose weight regain the lost weight. Therefore, it is important to maintain an optimal metabolic rate. Among other things, protein will be your assistant in this matter. It is necessary so that you do not feel hungry, and your muscles grow strong and strong.

The daily protein requirement depends on a number of factors. A qualified nutritionist can most accurately calculate the required amount of nutrients. But there are a number of online calculators on the Internet that make it possible to do the calculations yourself.