Sources of energy in the human body. Energy sources for living organisms

Carbohydrates and fats are one of the sources of energy for the human body. They play a special role in the nutrition of older people. At the same time, the amount of these natural organic compounds in the food of the elderly should be moderate. It is advisable to limit carbohydrates mainly due to simple sugar and sweets, while vegetables, fruits and grains should be in sufficient quantities in the diet. At the same time, one should strive to increase the proportion of vegetable oils in the diet to half the total amount of fat. But all these recommendations should be strictly controlled. Often there are cases when the desire to achieve high therapeutic efficacy from the use of, for example, vegetable oils is provided by an uncontrolled increase in its diet to quantities that cause only a violent laxative effect, adversely affecting the patient's health. That is why it is important for the clinician to pay special attention to many fundamentally important metabolic aspects of carbohydrate and fat metabolism. This knowledge will help him to properly organize well-coordinated work in the "laboratory" of the body of an elderly person.

Types of carbohydrates

Carbohydrates are polyatomic aldehyde or keto alcohols, which are subdivided depending on the amount of monomers into mono-, oligo- and polysaccharides. The main representatives of carbohydrates are presented in table 1.

Table 1. The main representatives of carbohydrates

Monosaccharides (glucose, fructose, galactose, etc.), oligosaccharides (sucrose, maltose, lactose) and digestible polysaccharides (starch, glycogen) are the main sources of energy, and also perform a plastic function.

Indigestible polysaccharides (cellulose, hemicellulose, etc.), or dietary fiber, play an important role in nutrition, participating in the formation of feces, regulating the motor function of the intestine, acting as sorbents (see Table 2). Pectins (colloidal polysaccharides) and propectins (complexes of pectins with cellulose), gums, mucus are used in diet therapy due to their detoxifying effect. Dietary fiber also includes non-carbohydrate lignin.

Digestible carbohydrates in the small intestine are broken down to disaccharides, and then, by parietal digestion, to monosaccharides.

Table 2. The role of indigestible polysaccharides (dietary fiber) in nutrition

Glucose metabolism

Absorption of monosaccharides occurs by facilitated diffusion and active transport, which ensures their high absorption even at low concentrations in the intestine. The main carbohydrate monomer is glucose, which is initially delivered to the liver through the portal vein system, and then either metabolized in it, or enters the general circulation and is delivered to organs and tissues.

Glucose metabolism in tissues begins with the formation of glucose-6-phosphate, which, unlike free glucose, is not able to leave the cell. Further transformations of this compound go in the following directions:

• splitting again to glucose in the liver, kidneys and intestinal epithelium, which allows you to maintain a constant level of sugar in the blood;
• deposit form synthesisglucose - glycogen - in the liver, muscles and kidneys;
• oxidation along the main (aerobic) pathway of catabolism;
• oxidation along the path of glycolysis (anaerobic catabolism), which provides energy for intensively working (muscle tissue) or mitochondrial-deprived (erythrocytes) tissues and cells;
• by the pentose phosphate pathway of transformations occurring under the action of the coenzyme form of vitamin B1 , during which the products used in the synthesis of biologically significant molecules (NADP∙H2, nucleic acids) are generated.

Thus, glucose metabolism can occur in various ways, using its energy potential, plasticity, or ability to be deposited.

Energy for the body

The provision of tissues with glucose as an energy material occurs due to exogenous sugars, the use of glycogen reserves and the synthesis of glucose from non-carbohydrate precursors.

In the basal (pre-absorption) state, the liver produces glucose at a rate equal to its utilization throughout the body. Approximately 30% of glucose production by the liver occurs due to glycogenolysis, and 70% - as a result of gluconeogenesis. The total amount of glycogen in the body is approximately 500 g.

If there is no exogenous supply of glucose, its reserves are depleted after 12-18 hours. In the absence of reserve glycogen, as a result of starvation, the processes of oxidation of another energy substrate, fatty acids, sharply increase. At the same time, the rate of gluconeogenesis increases, aimed primarily at providing the brain with glucose, for which it is the main source of energy.

Synthesis of glucose

From amino acids, lactate, pyruvate, glycerol and fatty acids with an odd carbon chain, glucose is synthesized. Most amino acids are capable of being glucose precursors, but, as mentioned above, alanine plays the main role in this. About 6% of endogenous glucose is synthesized from amino acid sources, from glycerol, pyruvate and lactate, respectively, 2, 1 and 16%. The contribution of fatty acids to gluconeogenesis is insignificant, since only a small percentage of them have an odd carbon number.

In the post-absorption state, the liver transforms from an organ that produces glucose into a storage organ. With an increase in the concentration of glucose, the rate of its utilization by peripheral tissues almost does not change, therefore, the main mechanism for its elimination from the bloodstream is precisely the deposition. Only a small part of excess glucose is directly involved in lipogenesis, which occurs in the liver and in adipose tissue. These features of carbohydrate metabolism become significant when highly concentrated glucose solutions are administered parenterally.

Self-service principle

The metabolism of glucose in the muscles compared with the liver is reduced. After all, the liver provides carbohydrates to all organs and tissues, and the muscles work in accordance with the principle of self-service. Here, the creation of a stock of glycogen at rest and the use of it and newly incoming glucose during work takes place. Glycogen stores in muscles do not exceed 1% of their mass.

The main energy needs of intensively working muscles are met by the oxidation of fat metabolism products, and glucose is used here to a much lesser extent. In the process of glycolysis, pyruvate is formed from it, which is utilized by skeletal muscles. With an increase in the level of work, muscle tissue enters anaerobic conditions, transforming pyruvate into lactate. It diffuses into the liver, where it is used for glucose resynthesis, and can also be oxidized in the myocardium, which almost always works under aerobic conditions.

Essential Hormones

Insulin plays a key role in the regulation of carbohydrate metabolism, ensuring the entry of glucose into the cell, activating its transport through cell membranes, and accelerating oxidation. In addition, it stimulates glycogen formation, lipo- and proteinogenesis. Glycogenolysis, lipolysis and gluconeogenesis are simultaneously inhibited.

Glucagon, on the contrary, activates the processes leading to an increase in the concentration of glucose in the blood. Glucocorticosteroids act in the direction of hyperglycemia by stimulating the production of glucose by the liver. Adrenaline enhances glycogen mobilization. Growth hormone increases the secretion of both glucagon and insulin, which leads to both an increase in glucose deposition and an increase in utilization. Somatostatin inhibits the production of growth hormone and indirectly inhibits the production of insulin and glucagon.

Fructose Pathway

Specific conversions of other digestible carbohydrates are of lesser importance compared to glucose, since their metabolism mainly occurs through the formation of glucose. Special importance is attached to fructose, which is also a rapidly utilized source of energy and participates in lipogenesis even more easily than glucose. At the same time, the utilization of fructose that has not been converted into glucose-phosphate does not require insulin stimulation; accordingly, it is more easily tolerated in case of impaired glucose tolerance.

The plastic function of carbohydrates is their participation in the synthesis of glycoproteins and glycolipids, as well as the ability to act as precursors of triglycerides, non-essential amino acids, and be used in the construction of many other biologically significant compounds.

Norm of carbohydrates

It is known that for people of any age, carbohydrates should supply from 55 to 60% of the calorie content of the daily diet. With a decrease in physical activity (which is typical for older people), the body's need for food energy supply decreases. As noted above, the daily calorie requirement is reduced by 10% in every subsequent 10 years after reaching the age of 50. In this regard, the average daily norm for providing the body of an elderly and old person with carbohydrates is taken to be 300 and 250 g, respectively. However, a physically active lifestyle of older people, the preservation of their professional activities requires an increase in the indicated amounts of carbohydrates by 10-15 and even 20% (Levin S. R. , 1990; Toshev A. D., 2008).

Beware of obesity!

Carbohydrates in the body are used primarily as a source of energy for muscle work. In the absence of physical activity, excess carbohydrates in old age easily turn into fat. A particularly unfavorable effect in this regard is exerted by a dietary excess of easily digestible carbohydrates, such as di- and monosaccharides, which stimulate the transformation of all food nutrients without exception into adipose tissue and contribute to the development of obesity.

The noted metabolic features of an excess of carbohydrates, primarily simple ones, in the diet of older people determine one of the most important conditions for their rational and preventive nutrition - a particularly careful approach to organizing adequate nutrition: the energy balance of the diet with the actual energy consumption in the aging process.

Aging rate

It is important to draw the attention of clinicians to another fundamentally significant metabolic aspect of the excess amount of simple carbohydrates in the body of older people. It has been found that the intake of large amounts of simple carbohydrates, in addition to disturbances in carbohydrate metabolism and the accumulation of excess energy in natural and unnatural fat depots, contributes to a significant distortion of fat metabolism. We are talking about the hypercholesterolemic effect of an excess of low molecular weight carbohydrates, which in its pathophysiological effect resembles the role of saturated fats in the genesis, primarily of atherosclerosis and related diseases. The progression of the noted phenomena has a noticeably potentiating effect on the rate of aging of the body (Miles J., 2004).

An excess of easily digestible dietary carbohydrates most adversely affects the normal intestinal microbiocenosis. Under conditions of excessive carbohydrate nutrition in the body of an elderly person, pathological reproduction of aerobic intestinal microorganisms is activated, especially facultative, opportunistic pathogens - staphylococci, Proteus, Clostridia, Klebsiel, citrobacteria, etc. The alimentary genesis of intestinal dysbiosis provokes the appearance of the syndrome of fermentative intestinal dyspepsia and the symptom complex associated with this process enteral disorders, metabolic disorders, regulatory dysfunctions of many organs and systems of the body, i.e. the formation of many and many pathological phenomena in the body due to the fall of the controlling and regulating influence of normal intestinal endoecology on the most important functions of the body. Intestinal dysbiosis is one of the noticeable stimulators of the rate of development of aging, the formation of premature and pathological aging.

Saving fiber

The opposite effect has carbohydrates, which are polysaccharides and dietary fiber - pectin, hemicellulose, lignin and other polysaccharides that are poorly digested in the intestine. Of particular value is the fiber of vegetables and fruits, complex carbohydrates which are most conducive to the normalization of intestinal microflora. In old age, dietary fiber is an important means of normalizing the functioning of the intestines, reducing putrefactive processes in it.

Fat metabolism

Fats (lipids), represented in the body mainly by triglycerides (compounds of glycerol and fatty acids), are the most important energy substrate. Due to their high caloric density (9 kcal/g on average, compared to 4 kcal/g for glucose), fats make up over 80% of the body's energy stores.

Scanty transisomers

During the processing of vegetable oils - the creation of margarines - isomerization of unsaturated fatty acids occurs with the creation of trans-isomers, which lose some of the biological functions of their predecessors.

The energy value of individual triglycerides is determined by the length of the carbon chains of fatty acids, therefore, when using specialized enteral and parenteral products, their calorie content may be below average (for example, for preparations of triglycerides with an average carbon chain - 8 kcal / g). With a normal diet, fats provide up to 40% of the total caloric intake.

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Fatty acid

Fatty acids are divided into saturated and unsaturated (containing double chemical bonds). The source of saturated fatty acids is mainly animal food, unsaturated fatty acids - products of plant origin.

The nutritional value of fatty foods is determined by their triglyceride spectrum and the presence of other lipid factors. The synthesis of saturated and monounsaturated fatty acids is possible in the human body.

Of particular importance in dietology is attached to unsaturated fatty acids, which are essential nutritional factors. Polyunsaturated fatty acids (PUFAs), which carry the most important functions in the body (these are the precursors of a number of biologically active substances), must be supplied exogenously.

Essential fatty acids include linoleic and linolenic. Linoleic acid is metabolized in the body into arachidonic acid, and linolenic acid into eicosapentaenoic acid, which can enter the body with meat and fish products, but in small quantities (see Table 3), components of cell membranes, precursors of hormone-like substances. Linoleic acid and arachidonic acid formed from it belong to ω -6 fatty acids, linolenic acid and its metabolic products eicosapentaenoic and deoxohexaenoic acid belong to ω -3 fatty acids.

Deficiency of essential fatty acids in the diet primarily causes a violation of the biosynthesis of arachidonic acid, which is a large part of structural phospholipids and prostaglandins. The content of linoleic and linolenic acids largely determines the biological value of food products. Insufficiency of essential fatty acids develops mainly in patients who are on total parenteral nutrition without the use of fat emulsions.

Table 3 Major dietary sources of various fatty acids

Carbon chain length

Medium chain triglycerides (MCTs, MCTs) are more digestible than other types of triglycerides. They are hydrolyzed in the intestine without the participation of bile, more attacked by lipases. In addition, the introduction of medium chain triglycerides has a hypocholesterolemic effect, since they do not participate in the micellization necessary for cholesterol absorption.

The disadvantage of using preparations containing medium chain triglycerides is that they are used exclusively as an energy (but not plastic) substrate. In addition, the oxidation of such fatty acids leads to an intensive accumulation of ketone bodies and can exacerbate acidosis.

Sterols and phospholipids

Sterols and phospholipids are not essential nutritional factors, but play an important role in metabolism.

Phospholipids are essential components of the body. Their main role is to provide the fundamental structure of the membrane as a permeability barrier. The biosynthesis of structural phospholipids in the liver is aimed at providing them to the liver itself and other organs. Phospholipids have a lipotropic effect, facilitating the micelle formation of fats in the digestive tract, their transport from the liver, and stabilizing lipoproteins.

Sterols in animal products are represented by cholesterol, and in vegetable products they are a mixture of phytosterols.

Role of cholesterol

Cholesterol is a structural component of membranes and a precursor of steroids (hormones, vitamin D, bile acids). Replenishment of cholesterol occurs due to intestinal absorption and biosynthesis (1 g / day). The amount of cholesterol absorbed in the intestine is limited (0.3-0.5 g / day), and if it is excessive in food, it is excreted with feces.

Cholesterol absorption is inhibited by its plant structural analogs, phytosterols. Phytosterols themselves can also be included in endogenous lipid formations, but their participation is minimal. With excessive intake of cholesterol with food, its synthesis in the liver, intestines and skin practically stops.

Cholesterol coming from the intestine as part of chylomicrons is largely retained in the liver, where it is used to build hepatocyte membranes and in the synthesis of bile acids. As a result of reabsorption, about 40% of fats are returned to the body in the composition of bile. Cholesterol and bile acids that have not been reabsorbed in the intestines are the main route of cholesterol excretion from the body.

Lipid transport

In the bloodstream, lipids exist in transport forms: chylomicrons, very low density lipoproteins (VLDL), low density lipoproteins (LDL) and high density lipoproteins (HDL). In enterocytes, chylomicrons and VLDL are formed, in hepatocytes - VLDL and HDL, in blood plasma - HDL and LDL.

Chylomicrons and VLDL transport mainly triglycerides, while LDL and HDL transport cholesterol. Cholesterol-containing lipoproteins regulate the balance of cholesterol in cells: LDL provides the needs, and HDL prevent excess accumulation.

There are five types of dyslipoproteinemias. Type I is associated with a violation of chylomicron lysis, type IIa is the result of a violation of LDL breakdown and a decrease in cholesterol entry into the cell, type II is characterized by a slowdown in the breakdown of VLDL, type IV is associated with an increase in triglyceride synthesis in the liver as a result of hyperinsulinism, the development mechanisms of types IIb and V are not exactly known .

The composition of triglycerides and lipoproteins is strongly influenced by the composition of food. Animal products, including predominantly polyunsaturated fatty acids and cholesterol, have an atherogenic effect, blood levels of HDL and triglycerides. Conversely, unsaturated fatty acids (sourced from vegetable oils), and in particular ω-3 fatty acids (found in fish oil), have a preventive effect (see Table 4).

Table 4 Effect of fatty acids on the lipoprotein spectrum

Note: - increase, ↓ - decrease.

The key role of the liver

As in the metabolism of carbohydrates, the liver plays a leading role in lipid metabolism. Processes such as the biosynthesis of cholesterol, bile acids and phospholipids are localized exclusively in the liver. In the metabolism of other lipids, it has modifying and regulatory functions.

In contrast to rich glycogen reserves, the liver contains practically no triglyceride reserves of its own (less than 1%), but it occupies a key position in the processes of mobilization, consumption and synthesis of fats in other tissues. This role is based on the fact that almost all fat metabolism flows through the liver: food lipids in the form of chylomicrons enter it through the general bloodstream through the hepatic artery; free fatty acids mobilized from fat depots are transported in the form of complexes with albumin; bile salts, reabsorbed in the intestine, again come through the portal vein.

The energy potential of lipids provides more than half of the basic energy needs of most tissues, which is especially pronounced in starvation conditions. During starvation or reduced glucose utilization, adipose tissue triglycerides are hydrolyzed into fatty acids, which in organs such as the heart, muscles, and liver undergo intense β-oxidation to form ATP.

Demand for ketone bodies

The products of incomplete utilization of fats by the liver are ketone bodies. These include acetoacetic acid, β-hydroxybutyrate, and acetone.

Normally, ketones are formed in small amounts and are completely utilized as an energy source by nervous tissue, skeletal and visceral muscles. Under conditions of accelerated catabolism of fatty acids and/or reduced utilization of carbohydrates, the synthesis of ketones may exceed the possibility of their oxidation by extrahepatic organs and lead to the development of metabolic acidosis. Diet carbohydrates have an inhibitory effect on ketogenesis.

The brain and nervous tissue practically do not use fats as an energy source, since β-oxidation does not occur here. However, these tissues can use ketone bodies. Normally, the proportion of ketone body oxidation processes is insignificant compared to glucose catabolism. However, under fasting conditions, ketone bodies become an important alternative source of energy.

Ketones are also used by the muscles, along with the utilization of glucose and β-oxidation that occurs here. With a slight physical load, the muscles oxidize mainly carbohydrates, an increase in the intensity and duration of work requires the predominance of fat catabolism, β-oxidation in most tissues is stimulated by the lipid carrier carnitine, but it is especially important for muscle tissue.

PUFA oxidation

Free radical forms of oxygen cause the processes of peroxidation, which are primarily subject to polyunsaturated fatty acids. This is a physiological process that regulates cell activity. However, with excessive formation of free radicals, their oxidative activity leads to disruption of the structure and death of the cell. To limit peroxidation, there is an antioxidant defense system that inhibits the formation of free radicals and decomposes toxic products of their oxidation. The functioning of this system largely depends on alimentary antioxidants: tocopherols, selenium, sulfur-containing amino acids, ascorbic acid, rutin.

Metabolism of carbohydrates and fats

The synthesis of fatty acids (with the exception of essential ones) can occur from any substances for which the end product of metabolism is acetyl-Co-A, but carbohydrates are the main source of lipogenesis. With an excessive amount of glucose in the liver (after eating) and sufficient glycogen stores, glucose begins to decompose to fatty acid precursors. That is, if the consumption of carbohydrates exceeds the energy needs of the body, their excess is further converted into fats.

The regulation of fatty acid and glucose metabolism are closely related: increased fatty acid oxidation inhibits glucose utilization. Therefore, infusion of fat emulsions with a corresponding increase in the level of free fatty acids in the blood weakens the effect of insulin on glucose utilization and stimulates hepatic gluconeogenesis. This point is important in parenteral nutrition of patients with initially impaired glucose tolerance.

The Secret of Relationship

The relationship between the exchange of basic nutrients is carried out due to the existence of common precursors and intermediate products of metabolism.

The most important common metabolic product involved in all metabolic processes is acetyl-Co-A. The flow of substances towards lipogenesis from carbohydrate and protein sources through acetyl-Co-A is unidirectional, since there is no mechanism in the body that ensures the conversion of this two-carbon substance into three-carbon compounds necessary for gluconeogenesis or the synthesis of nonessential amino acids. Although the formation of small amounts of intermediate three-carbon products occurs during lipid catabolism, it is insignificant.

The common final pathway of all metabolic systems is the Krebs cycle and respiratory chain reactions. The citric acid cycle is a supplier of carbon dioxide for the reactions of fatty acid synthesis and gluconeogenesis, the formation of urea and purines and pyrimidines. The relationship between the processes of carbohydrate and nitrogen metabolism is achieved through the intermediate products of the Krebs cycle. Other links of this cycle are precursors of liponeogenesis.

As noted above, the main role in nutrient metabolism is played by the liver (see Table 5).

Table 5 The role of the liver in the metabolism of proteins, fats and carbohydrates

The rate of fat consumption

The physiological upper limit of the quantitative provision of an elderly person with dietary fats should be considered 1 g/kg for the age of 60-75 years and 0.8 g/kg for the age over 75 years. If at a young and middle age 30% of the total amount of fat consumed should be represented by fats of vegetable origin, and 70%, respectively, by animals, then in elderly and senile people, the quantitative ratio of vegetable and animal fats to a certain extent changes towards an increase in the proportion vegetable fats up to 40% in the elderly and up to 50% in people over 75 years of age (Goigot J. Et al., 1995 and others).

The risk of developing atherosclerosis associated with the consumption of foods rich in cholesterol and high fat intake does not seem to be as critical for older people as it is for middle-aged people. An increase in the quota of fats with an unsaturated (by hydrogen) chemical structure for the elderly, and even more so for the elderly, primarily has an antioxidant focus, significantly activating the sanitizing functions of the body, increasing the intensity of lipid peroxidation processes, intensifying the protection of cellular structures from free radical damage in various ways.

Gerontoprotective nutritional factors

An important direct and indirect metabolic aspect of vegetable fats in the body of an elderly person is the use of the stimulating capabilities of vegetable oils on various physiological processes of the gastrointestinal tract and other systems, starting with the activation of intestinal motility, biliary dynamics (cholekinetic and choleretic components), enhancing the sorption properties of enterocytes and etc. and ending with multifaceted effects, a positive effect on the processes of cell regeneration, membrane function, cell differentiation, and the synthesis of many prostaglandins.

Polyunsaturated fatty acids of vegetable fats, in contrast to the predominantly energy essence of saturated fatty acids of animal fats, in an aging body every year of its life play more and more important functions for counteracting aging: they provide ever-increasing needs for vitamins and biologically active substances of an antioxidant orientation, restore a progressive decline cytoprotective properties of cellular structures, especially vital organs, level involutional disorders of cell membranes and much, much more.

In their physiological essence, polyunsaturated fatty acids, along with the so-called natural peptide bioregulators, can be considered as gerontoprotective nutritional factors, the physiological significance of which is great at any period of a person’s life, but especially increases with the onset of elderly, especially senile age.

Energy sources for the human body are proteins, fats, carbohydrates, which make up 90% of the dry weight of all nutrition and supply 100% of energy. All three nutrients provide energy (measured in calories), but the amount of energy in 1 gram of the substance is different:

• 4 kilocalories per gram of carbohydrates or proteins;
• 9 kilocalories per gram of fat.

A gram of fat has 2 times more energy for the body than a gram of carbohydrates and proteins.

These nutrients also differ in how quickly they deliver energy. Carbohydrates are delivered faster and fats are slower.

Proteins, fats, carbohydrates are digested in the intestine, where they are broken down into basic units:

• carbohydrates in sugar
• proteins in amino acids
• fats in fatty acids and glycerol.

The body uses these basic units to create the substances it needs to perform basic life functions (including other carbohydrates, proteins, fats).

Types of carbohydrates

Depending on the size of the carbohydrate molecules, they can be simple or complex.

• Simple Carbohydrates: Various types of sugars, such as glucose and sucrose (table sugar), are simple carbohydrates. These are small molecules, so they are quickly absorbed by the body and are a quick source of energy. They quickly increase blood glucose (blood sugar levels). Fruits, dairy products, honey, and maple syrup are high in simple carbohydrates, which provide the sweet taste in most candies and cakes.
• Complex Carbohydrates: These carbohydrates are made up of long strings of simple carbohydrates. Because complex carbohydrates are large molecules, they must be broken down into simple molecules before they can be absorbed. Thus, they tend to provide energy to the body more slowly than simple ones, but still faster than protein or fat. This is because they are digested more slowly than simple carbohydrates and are less likely to be converted to fat. They also raise blood sugar levels at a slower rate and at lower levels than regular ones, but for a longer time. Complex carbohydrates include starches and proteins found in wheat products (bread and pasta), other grains (rye and corn), beans, and root vegetables (potatoes).

Carbohydrates can be:

• refined
• unrefined

refined– processed , fiber and bran, as well as many of the vitamins and minerals they contain, are removed. Thus, the metabolism processes these carbohydrates quickly and provides little nutrition, although they contain about the same number of calories. Refined foods are often fortified, meaning vitamins and minerals are artificially added to increase nutritional value. A diet high in simple or refined carbohydrates tends to increase the risk of obesity and diabetes.

unrefined carbohydrates from plant foods. They contain carbohydrates in the form of starch and fiber. These are foods such as potatoes, whole grains, vegetables, fruits.

If people consume more carbohydrates than they need, the body stores some of these carbohydrates in the cells (as glycogen) and converts the rest into fat. Glycogen is a complex carbohydrate to convert into energy and is stored in the liver and muscles. Muscles use glycogen for energy during periods of intense exercise. The amount of carbohydrates stored as glycogen can provide calories per day. Several other body tissues store complex carbohydrates that cannot be used as an energy source for the body.

Glycemic index of carbohydrates

The glycemic index of carbohydrates represents how quickly their consumption raises blood sugar levels. The range of values ​​is from 1 (slowest absorption) to 100 (fast, net glucose index). However, how quickly levels actually rise depends on the foods ingested.

The glycemic index is generally lower for complex carbohydrates than for simple carbohydrates, but there are exceptions. For example, fructose (sugar in fruits) has little effect on blood sugar levels.

The glycemic index is influenced by processing technology and food composition:

• processing: processed, chopped or finely ground foods tend to have a high glycemic index
• type of starch: different types of starch are absorbed differently. Potato starch is digested and relatively quickly absorbed into the blood. Barley is digested and absorbed much more slowly.
• fiber content: The more fiber a food has, the harder it is to digest. As a result, sugar is more slowly absorbed into the blood.
• fruit ripeness: ripe fruit, more sugar in it and the higher its glycemic index
• fat or acid content: contains more fat or acid food, slowly digested and slowly its sugars are absorbed into the blood
• Cooking: How food is prepared can affect how quickly it is absorbed into the bloodstream. Generally, cooking or chopping food increases its glycemic index as it is easier to digest and absorb after the cooking process.
• other factors : The body's nutritional processes vary from person to person, how quickly carbohydrates are affected by conversion to sugar and absorption. How well the food is chewed and how quickly it is swallowed is important.

Glycemic index of some foods

The glycemic index is an important parameter, because carbohydrates increase blood sugar, if quickly (with a high glycemic index) then insulin levels increase. An increase in insulin can lead to low blood sugar (hypoglycemia) and hunger, which tends to consume excess calories and gain weight.

Carbohydrates with a low glycemic index do not increase insulin levels much. As a result, people feel full longer after eating. Consumption of low glycemic carbohydrates also leads to healthier cholesterol levels and reduces the risk of obesity and diabetes in people with diabetes, the risk of complications due to diabetes.

Despite the link between low glycemic index foods and improved health, using the index to select foods does not automatically lead to healthy eating.

For example, the high glycemic index of potato chips and some candies are not a healthy choice, but some high glycemic foods contain valuable vitamins and minerals.

Thus, the glycemic index should only be used as a general guide to food selection.

Glycemic load of foods

The glycemic index measures how quickly carbohydrates in food are absorbed into the blood. It does not include the amount of carbohydrates in food, which are important.

Glycemic load, a relatively new term, includes the glycemic index and the amount of carbohydrates in a food.

Foods such as carrots, bananas, watermelon, or wholemeal bread may have a high glycemic index but are relatively low in carbohydrates and thus have a low glycemic load of foods. These foods have little effect on blood sugar levels.

Proteins in foods

Proteins are made up of a structure called amino acids and form complex formations. Because proteins are complex molecules, it takes longer for the body to absorb them. As a result, they are a much slower and longer source of energy for the human body than carbohydrates.

There are 20 amino acids. The human body synthesizes some of the components in the body, but it cannot synthesize 9 amino acids - called essential amino acids. They must be included in the diet. Everyone needs 8 of these amino acids: isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Babies also need the 9th amino acid, histidine.

The percentage of protein that the body can use to synthesize essential amino acids varies. The body can use 100% of the protein in an egg and a high percentage from milk and meat proteins, but can use slightly less than half the protein from most vegetables and grains.

The body of any mammal needs protein to maintain and replace tissue growth. Protein is not usually used as an energy source for the human body. However, if the body is not getting enough calories from other nutrients or stored body fat, protein is used for energy. If there is more protein than needed, the body converts the protein and stores its components as fat.

The living body contains a large amount of protein. Protein, the main building block in the body and is the main component of most cells. For example, muscles, connective tissue and skin are all built from protein.

Adults should eat about 60 grams of protein per day (1.5 grams per kilogram of body weight, or 10-15% of total calories).

Adults who are trying to build muscle need a little more. Children also need more protein as they grow.

Fats

Fats are complex molecules made up of fatty acids and glycerol. The body needs fats for growth and as a source of energy for the body. Fat is also used for the synthesis of hormones and other substances necessary for the functioning of the body (for example, prostaglandins).

Fats are a slow source of energy, but the most energy efficient type of food. Each gram of fat provides the body with about 9 calories, more than twice as much as supplied proteins or carbohydrates. Fats are an efficient form of energy and the body stores excess energy as fat. The body stores excess fat in the abdomen (omental fat) and under the skin (subcutaneous fat) to be used when more energy is needed. The body can also remove excess fat from blood vessels and organs, where it can block the flow of blood, and from damaged organs, often causing serious problems.

Fatty acid

When the body needs fatty acids, it can make (synthesize) some of them. Some acids, called essential fatty acids, cannot be synthesized and must be consumed in the diet.

Essential fatty acids make up about 7% of the fat consumed in a normal diet and about 3% of total calories (about 8 grams). They include linoleic and linolenic acids, which are present in some vegetable oils. Eicosapentaenoic and docosahexaenoic acids, which are essential fatty acids for brain development, can be synthesized from linoleic acid. However, they are also present in some marine fish products, which are a more efficient source.

Where is fat located?

Linoleic and arachidonic acids are both omega-6 fatty acids.

Linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid are omega-3 fatty acids.

A diet rich in omega-3 fatty acids may reduce the risk of atherosclerosis (including coronary artery disease). Lake trout and some deep sea fish are high in omega-3 fatty acids.

You need to consume enough omega-6 fatty acids

Types of fats

There are different types of fats

• monounsaturated
• polyunsaturated
• rich

Eating saturated fat increases cholesterol levels and the risk of atherosclerosis. Products derived from animals usually contain saturated fats, which tend to be solid at room temperature. Fats derived from plants usually contain monounsaturated or polyunsaturated fatty acids, which are usually liquid at room temperature. The exceptions are palm and coconut oil. They contain more saturated fats than other vegetable oils.

Trans fats (trans fatty acids) are another category of fat. They are artificial and are formed by the addition of hydrogen atoms (hydrogenation) of monounsaturated or polyunsaturated fatty acids. Fats can be fully or partially hydrogenated (saturated with water atoms). The main nutritional source of trans fats is partially hydrogenated vegetable oils in commercially prepared foods. Consumption of trans fats can negatively affect cholesterol levels in the body and may contribute to the risk of atherosclerosis.

Fats in the diet

• fat must be limited and make up less than 30% of total daily calories (or less than 90 grams per day)
• Saturated fat should be limited to 10%.

When fat intake is reduced to 10% or less of total daily calories, cholesterol levels drop dramatically.

Carbohydrates, proteins and fats are the main sources of energy necessary for human life and their quality is important for health.

So the main and only The source of energy in the body is the ATP molecule.(adenosine triphosphoric acid). Without it, neither contraction nor relaxation of muscle fibers is possible. Very often ATP is rightly called body's energy currency!

The chemical reaction that explains the process of releasing energy from ATP is as follows:

ATP + water –> ADP + F + 10 kcal,
where ADP is adenosine diphosphoric acid, P is phosphoric acid.

Under the action of water (hydrolysis), a molecule of phosphoric acid is split off from the ATP molecule, while ADP is formed and energy is released.

However, the supply of ATP in the muscles is extremely small. It lasts for a maximum of 1-2 seconds. How then can we exercise for hours at a time?

This explains the following reaction:

ADP + P + energy (creatine phosphate, glycogen, fatty acids, amino acids) –> ATP

Thanks to the last reaction, ATP resynthesis occurs. This reaction can only take place in the presence of reserve in the body of carbohydrates, fats and proteins. They are, in fact, true sources of energy and determine the duration of the load!

It is very important that the rates of the first and second reactions are different. As the intensity of the load increases, the rate of conversion of ATP to energy also increases. While the second reaction goes obviously at a lower rate. At some level of intensity, the second reaction can no longer compensate for the consumption of ATP. In this case, muscle failure occurs. The more trained the athlete, the higher the level of intensity at which this failure occurs.

Allocate two types of exercise: aerobic and anaerobic. In the first case, the process of ATP resynthesis (the second reaction indicated above) is possible only if there is a sufficient amount of oxygen. It is in this load mode, and this is a load of moderate power, after all glycogen stores have been exhausted, the body will willingly use fat as fuel for the formation of ATP. This mode largely determines such an indicator as IPC(maximum oxygen consumption). If at rest for all healthy people the MIC = 0.2-0.3 l / min, then under load this figure increases greatly and amounts to 3-7 l / min. The more trained the body (mainly, this is determined by the respiratory and cardiovascular systems), the greater the amount of oxygen consumed can pass through it per unit time (high MPC) and the faster the ATP resynthesis reactions proceed. And this, in turn, is directly related to an increase in the rate of oxidation of subcutaneous fat.

Conclusion: In training to reduce body fat, special attention should be paid to the intensity of the load. She must be moderately powerful. The volume of oxygen consumed should not exceed 70% of the IPC. Determining the IPC is a very complicated procedure, so you can focus on your own feelings: just try to avoid a shortage of oxygen supplied; when performing the exercise, there should not be a feeling of lack of air. You should also pay special attention to the training of the cardiovascular and respiratory systems, which mainly determine the capacity of oxygen consumed per unit time. By developing the fitness of these two systems, you thereby increase the rate of fat breakdown.

So, we have considered the aerobic pathway of ATP resynthesis. In the next issue, we will focus on two other mechanisms of ATP resynthesis (anaerobic), which proceed with the use of creatine phosphate and glycogen.

PHYSIOLOGY OF METABOLISM AND ENERGY. BALANCED DIET.

Lecture plan.

The concept of metabolism in the body of animals and humans. Sources of energy in the body.

Basic concepts and definitions of the physiology of metabolism and energy.

Methods for studying energy metabolism in humans.

The concept of rational nutrition. Rules for compiling food rations.

The concept of metabolism in the body of animals and humans. Sources of energy in the body.

The human body is an open thermodynamic system, which is characterized by the presence of metabolism and energy.

Metabolism and energy is a set of physical, biochemical and physiological processes of the transformation of substances and energy in the human body and the exchange of substances and energy between the body and the environment. These processes occurring in the human body are studied by many sciences: biophysics, biochemistry, molecular biology, endocrinology and, of course, physiology.

Metabolism and energy exchange are closely interconnected, however, in order to simplify the concepts, they are considered separately.

Metabolism (metabolism)- a set of chemical and physical transformations that occur in the body and ensure its vital activity in conjunction with the external environment.

In metabolism, two directions of processes are distinguished in relation to the structures of the body: assimilation or anabolism and dissimilation or catabolism.

Assimilation(anabolism) - a set of processes for the creation of living matter. These processes consume energy.

Dissimilation(catabolism) - a set of processes of decay of living matter. As a result of dissimilation, energy is reproduced.

The life of animals and humans is a unity of the processes of assimilation and dissimilation. The factors connecting these processes are two systems:

ATP - ADP (ATP - adenosine triphosphate, ADP - adenosine diphosphate;

NADP (oxidized) - NADP (reduced), where NADP - nicotine amide diphosphate.

The mediation of these compounds between the processes of assimilation and dissimilation is ensured by the fact that ATP and NADP molecules act as universal biological energy accumulators, its carrier, a kind of "energy currency" of the body. However, before energy is stored in ATP and NADP molecules, it must be extracted from the nutrients that enter the body with food. These nutrients are known to you proteins, fats and carbohydrates. In addition, it should be added that nutrients perform not only the function of energy suppliers, but also the function of suppliers of building material (plastic function) for cells, tissues and organs. The role of various nutrients in the implementation of the plastic and energy needs of the body is not the same. Carbohydrates primarily perform an energy function, the plastic function of carbohydrates is insignificant. Fats equally perform both energy and plastic functions. Proteins are the main building material for the body, but under certain conditions they can also be sources of energy.

Sources of energy in the body.

As noted above, the main sources of energy in the body are nutrients: carbohydrates, fats and proteins. The release of energy contained in food substances in the human body proceeds in three stages:

Stage 1. Proteins are broken down into amino acids, carbohydrates into hexoses, for example, into glucose or fructose, fats into glycerol and fatty acids. At this stage, the body mainly spends energy on the breakdown of substances.

Stage 2. Amino acids, hexoses and fatty acids in the course of biochemical reactions are converted into lactic and pyruvic acids, as well as into Acetyl coenzyme A. At this stage, up to 30% of potential energy is released from food substances.

Stage 3. With complete oxidation, all substances are broken down to CO 2 and H 2 O. At this stage, in the metabolic Krebs boiler, the remaining part of the energy, about 70%, is released. In this case, not all of the released energy is accumulated in the chemical energy of ATP. Part of the energy is dissipated into the environment. This heat is called primary heat (Q 1). The energy accumulated by ATP is further spent on various types of work in the body: mechanical, electrical, chemical and active transport. In this case, part of the energy is lost in the form of the so-called secondary heat Q 2 . See diagram 1.

Carbohydrates

biological oxidation

H 2 O + CO 2 + Q 1 + ATP

Mechanical work

+ Q 2