Biochemical Foundations of Human Vital Activity - Volkov N.I., Nesen E.N. 2000

Biochemistry of Sports
Biochemical Foundations of Athletes' Rational Nutrition
The role of individual dietary chemical components in supporting muscular activity

The main Cell/6.html">Chemical Components of food include the following six groups of substances: energy suppliers (CARBOHYDRATES, fats, Proteins), Essential Amino Acids, Essential Fatty acids, Vitamins, minerals, and Water (see Table 39). Each of these substances performs a specific function in the body's vital activity and influences physical performance.

The primary sources of energy in body Tissues are carbohydrates and fats. Fats also perform a structural function. While proteins can serve as an energy source, their main function is structural. Vitamins are components of many Enzymes and act as regulators of various metabolic processes. Minerals also play a regulatory role and form part of The Structure of various tissues—especially bone—as well as Blood. Water creates the body's internal environment and ensures that Chemical Reactions take place smoothly.

Although The Human Body is capable of synthesizing and storing many nutrients, some cannot be synthesized internally. These are known as essential dietary factors and must be obtained from food. A deficiency in these elements disrupts numerous metabolic processes, impairs adaptation during muscular activity, and can lead to various diseases.

The Role of Carbohydrates in Supporting Muscular Activity

Carbohydrates occupy one of the most crucial places in Human Nutrition, as they serve as the primary source of energy during intense physical exertion (Fig. 212). The duration of aerobic exercise, the maintenance of a high level of endurance, and the onset of fatigue all depend on carbohydrate reserves in the skeletal Muscles and Liver. Dietary carbohydrates ensure an adequate Blood Glucose Level—the principal energy substrate for the Brain—as well as the accumulation of Glycogen reserves in skeletal muscles and the liver.

Specific Applications of Different types of carbohydrates. Carbohydrates are found mainly in plant-based foods (bread, cereals, pasta, potatoes, sugar, vegetables, and fruits) in the form of mono-, di-, and Polysaccharides (see Chapter 9). Dietary di- and polysaccharides undergo Enzymatic Hydrolysis in the Digestive System and are converted primarily into glucose.

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Fig. 212 Relative contribution of carbohydrates and fats to running energetics depending on exercise intensity

Dietary Monosaccharides are represented mainly by glucose and fructose, which are found in many fruits and honey and are commonly referred to as sugars. They enter the body either in free form or are formed during Digestion from dietary di- and polysaccharides. Consuming a large amount of free glucose and its rapid absorption into the bloodstream (it appears in the blood just 15–20 minutes after a meal) leads to hyperglycemia. This stimulates the Pancreas to secrete the hormone Insulin, which ensures the uptake of glucose into tissues where it is used to synthesize glycogen, or—in the case of a significant surplus—fats. Following insulin action, blood glucose levels drop, which may lead to hypoglycemia and general weakness. Systematic stimulation of the pancreas can contribute to The Development of Diabetes Mellitus. Therefore, the proportion of monosaccharides in the diet, especially among older adults, should be limited to no more than 25–35% of total carbohydrate intake.

In clinical practice, free glucose is used to rapidly elevate blood concentration and improve tissue nourishment. In sports practice, glucose is administered during exercise and recovery periods to accelerate the restoration of glycogen stores. However, taking glucose 1.5–3 hours before long-term physical exertion is not recommended, particularly during competitions, as it accelerates the depletion of glycogen reserves and inhibits fat utilization. Fructose is frequently used instead of glucose to replenish liver glycogen. Although fructose is absorbed into the bloodstream from the gastrointestinal tract at a slower rate and does not stimulate pancreatic function, it restores glycogen at half The rate of glucose and other carbohydrates.

Disaccharides in plant foods are represented by sucrose, the main component of table sugar and many sweets (candies, cakes, preserves). During The breakdown of polysaccharides in the digestive system, the disaccharide maltose is formed, which further breaks down into two glucose molecules. Sucrose breaks down into glucose and fructose. The simultaneous consumption of large amounts of sucrose, much like monosaccharides, can cause hyperglycemia and its associated consequences; thus, it is justified only when a rapid restoration of energy reserves is required.

Milk and dairy products contain the disaccharide lactose, or "milk sugar." This is the primary dietary carbohydrate for infants during their first year of life. In adults, lactose digestion can sometimes be impaired, leading to recommendations to exclude dairy products from the diet. However, physicians refute this view, especially since Fermented milk products are virtually lactose-free.

Dietary polysaccharides are represented mainly by starch, found in plant foods (potatoes, cereals, bread, rice, etc.), and glycogen, known as "animal starch." In the human digestive system, starch is slowly broken down into glucose molecules, which are gradually absorbed into the bloodstream without causing blood hyperglycemia. Therefore, polysaccharides should predominate in the diet (up to 65%). Glycogen is ingested with food in small quantities (5–15 g ⋅ day^-1).

Individual groups of carbohydrates differ in their accessibility to hydrolytic enzymes in the gastrointestinal tract and the rate at which glucose enters the blood, a characteristic known as the glycemic index. Foods are classified into those with high, medium, and low glycemic indices, the consumption of which leads to varying degrees of increase in blood glucose levels.

Dietary fibers are plant polysaccharides that are not broken down during human digestion. They include Cellulose, hemicellulose, pectin, and Lignin. They pass through the gastrointestinal tract unchanged and are therefore referred to as ballast substances.

Although dietary fibers are not nutrients, they play a vital regulatory role in digestive processes. They accelerate intestinal transit, promote the secretion of digestive juices and Bile, stimulate the Elimination of Cholesterol, slow down Glucose Absorption following a high sugar intake, and bind toxic substances to facilitate their removal from the intestine. A regular intake of dietary fiber lowers the risk of atherosclerosis and Cancer while improving gastrointestinal function. Nevertheless, excessive amounts can impair the absorption of minerals (Fe, Ca, Mg, Cu) and Fat-soluble vitamins. Dietary fibers are found in rye bread, vegetables (cabbage, beets, carrots), and fruits (apples, prunes). The recommended daily intake is 10–15 g ⋅ day^-1.

Carbohydrate intake after physical exertion. The daily carbohydrate requirement for an adult depends on the body's Energy Expenditure and averages 300–400 g ⋅ day^-1.

For athletes, Carbohydrate Requirements increase due to the additional energy expended during training and competition. In certain sports, energy expenditure is nearly 1.5–2 times higher than that of individuals engaged in physical labor, raising the average carbohydrate requirement to 400–700 g ⋅ day^-1. Because energy expenditure depends on body mass and the level of physical activity, The amount of carbohydrates needed to replenish expended energy can be calculated by multiplying body mass (kg) by the carbohydrate factor (g ⋅ kg^-1 ⋅ day^-1) corresponding to the given activity level (Table 44).

In endurance sports with intense training and During the first 24 hours post-exercise, it is recommended to consume 10 g of carbohydrates per 1 kg of body mass per day, whereas in strength and speed-strength sports, the recommendation is 7 g per 1 kg of body mass. For a 70 kg athlete, this amounts to 700 and 490 g ⋅ day^-1, respectively.

TABLE 44 Carbohydrate intake at varying levels of physical activity

For athletes, simple carbohydrate (sugar) intake may be increased up to 100 g ⋅ day^-1 or more. For sedentary individuals and older adults, sugar intake should not exceed 50 g.

Reducing dietary carbohydrate intake below 300 g intensifies the breakdown of cellular proteins, fat oxidation, and the Formation of Ketone bodies, which can lead to acidosis. Systematic excessive dietary carbohydrate intake can lead to obesity, atherosclerosis, and diabetes mellitus, as surplus carbohydrates are converted into fats and cholesterol.

Glycogen reserves in skeletal muscles and the liver are depleted after 2–3 hours of intense Physical Exercise corresponding to 60–80% of $\text{VO}_2\text{max}$. They can be exhausted even faster during high-power work within the range of 90–130% of $\text{VO}_2\text{max}$ (see Chapter 9), yet they recover quite slowly—at a rate of about 5% per hour. Therefore, specific conditions must be established during the recovery period to accelerate glycogen replenishment.

The rate of glycogen restoration in muscles and the liver following physical exertion depends on the speed of carbohydrate delivery to the body, the type of carbohydrates consumed, and the timing of carbohydrate intake during the recovery period.

It takes about 20 hours to fully restore Muscle glycogen stores after exhaustive physical exertion on a carbohydrate-rich diet, and even longer with an unbalanced diet. Proper timing of carbohydrate intake after a competition or intense workout promotes more efficient glycogen replenishment. Research shows that consuming carbohydrates (50 g or more) immediately following high-intensity endurance exercise (within the first 20 min) and then every 2 h helps restore muscle glycogen levels much faster. Faster muscle glycogen resynthesis occurs with glucose and sucrose (but not fructose) when consuming foods with a high glycemic index (Table 45).

Athletic performance in cyclic sports largely depends on glycogen reserves in the muscles and liver; therefore, athletes must approach competitions with maximal muscle glycogen stores. To achieve this, a "glycogen loading" or carbohydrate supercompensation method is used. First, glycogen stores in the muscles and liver are depleted through intense training over several days combined with carbohydrate restriction. This is followed by a three-day high-carbohydrate diet to reach the glycogen supercompensation phase by the time of the competition (Fig. 213). This method helps increase muscle glycogen stores by 20–40%.

TABLE 45. Foods that provide 50 g of carbohydrates

Fig. 213 Effect of the glycogen loading method on muscle glycogen levels: mixed diet (1), high-carbohydrate diet (2), and low-carbohydrate diet (3)

During competition periods, energy expenditure for a workload of identical volume increases by 26–29% compared to training sessions, so carbohydrate intake should be increased accordingly. To prevent fatigue associated with depleted glycogen stores during prolonged physical exertion, it is recommended to consume about 30–60 g of high-glycemic carbohydrates every hour starting from the beginning of the competition, preferably in liquid form.

The Role of Fats in Muscle Activity

Dietary fats, much like carbohydrates, serve as essential energy substrates during prolonged, low-intensity exercise up to 50% VO_2max (see Fig. 212). Furthermore, they supply Unsaturated fatty acids that cannot be synthesized by the body yet perform critical biological Functions. Unlike carbohydrates, fat reserves in the human body are virtually inexhaustible (see Chapter 10).

The Biological value of dietary fats depends on their content of essential unsaturated fatty acids, particularly polyunsaturated ones.

Utilization of specific dietary fats. Dietary fats primarily consist of triglycerides (neutral fats), which account for about 98% of total fat intake, alongside Phospholipids and cholesterol (2%). Their chemical composition is discussed in Chapter 10.

Triglycerides, or neutral dietary fats, enter the human body through animal and plant-based foods and can vary significantly in their fatty acid composition (Table 46). For instance, animal fats (solid fats)—excluding poultry and fish fats—mainly contain saturated fatty acids. Among unsaturated fatty acids, they may contain functionally important arachidonic acid. These fats also store vitamins A and D. Plant-based dietary fats contain large amounts of unsaturated fatty acids, primarily linoleic and linolenic acids, which are necessary for the body to synthesize other unsaturated fatty acids as well as Prostaglandins (regulators of hormone action). Unsaturated fatty acids improve the release into the bloodstream of fats synthesized in the liver, prevent Fatty liver disease, and exhibit a lipotropic effect.

TABLE 46. Fatty acid composition of PLANT AND ANIMAL fats (g per 100 g)

Triglycerides are the primary form of stored energy utilized during physical exercise. There are three pools of triglycerides: adipose tissue, muscle, and blood. Triglycerides from adipose tissue serve as the main energy source supporting muscle work. During lipolysis, they break down into glycerol and free fatty acids, which immediately enter the Circulatory system and are transported to various tissues. During muscular work, free fatty acids intensively flow into skeletal muscles, acting as an efficient energy substrate for their contraction.

Dietary phospholipids are chemically similar to the phospholipids found in the human body. They supply the body with polyunsaturated fatty acids, phosphorus, Choline, Inositol, and other substances.

Among the various phospholipids, lecithin is of paramount importance, exhibiting a lipotropic effect. It also helps prevent atherosclerosis and stimulates hematopoiesis, as well as overall GROWTH AND DEVELOPMENT. Lecithin is found in animal-based foods such as brain, fish roe, liver, egg yolk, and butter. The recommended daily human requirement for lecithin is 0.5 g.

Cholesterol does not serve as an energy substrate, yet it performs numerous vital functions in the body (see Chapter 10). Disruptions in its METABOLISM lead to cardiovascular diseases and other disorders. However, a direct correlation between dietary cholesterol intake and the development of diseases has not been conclusively proven. Nevertheless, the previously recommended daily cholesterol intake of 600 mg·day^-1 has recently been lowered to 300 mg·day^-1.

Sources of cholesterol include animal products such as liver, meat, chicken egg yolk, butter, and sour cream. Plant-based foods are virtually cholesterol-free. Vitamins A, E, C, PP, and prolonged physical activity help improve Cholesterol Metabolism.

Fat intake during physical exertion. The average daily requirement of an adult for fats is 80–100 g, which accounts for 30–35% of total caloric intake. Of this amount, animal fats make up 70%, and vegetable oil makes up 30% (25–45 g depending on work intensity).

Fat intake depends on daily energy expenditure and can be estimated as follows: for an energy expenditure of 1500 kcal—42 g, 2000 kcal—56 g, 2500 kcal—69 g, 3000 kcal—83 g, 3500 kcal—97 g, and 4000 kcal—111 g per day. Approximate fat content in common foods includes: 1 tablespoon of mayonnaise—23 g, 50 g of cheese—16 g, 85 g of pork chop—6 g, 5 g of butter—4 g, and 100 g of mashed potatoes—0.1 g. For residents of northern regions, fat intake increases by about 10%, whereas for residents of southern regions, it decreases by approximately 5%.

For athletes, a slight reduction in the proportion of dietary fat to 20–30% of total caloric intake is recommended, as high-fat diets do not enhance athletic performance.

Fats are intensively utilized for the Energy supply of skeletal muscles and The Heart primarily during aerobic physical activity, i.e., in endurance sports. As the body adapts to such training, Lipids become a more significant energy source for working muscles compared to carbohydrates.

Consuming a high-fat meal is discouraged 1.5–2 hours before exercise and immediately following prolonged and intense physical exertion, as fats will hinder the utilization of fatty acids mobilized from adipose tissue and promote fat accumulation in the liver. Excessive fat consumption, as well as eliminating fats entirely from the diet, negatively impacts human health and physical performance.

Certain ergogenic substances can enhance fat mobilization during muscular activity and their utilization by tissues, thereby helping to spare muscle glycogen stores. These include caffeine, which promotes triglyceride breakdown in tissues, and carnitine, which accelerates The transport of fatty acids into the Mitochondria and their subsequent oxidation.

The Role of Proteins in Muscle Activity

Proteins perform numerous biological functions in the body, the primary ones being building, growth, development, and repair of all cellular structures, REGULATION OF METABOLISM (Hormones and enzymes), and, in certain cases, serving as an energy source. All of this generates significant interest in The Use of proteins in athletic nutrition.

Biological Value of Dietary Proteins. During digestion, dietary proteins undergo hydrolysis and break down into 20 different amino acids, which enter the bloodstream, are delivered to tissues, and are used to synthesize new, unique human body proteins or in other metabolic processes. Proteins contain 8 essential amino acids, which the body desperately needs because it cannot synthesize them itself (see Chapter 12). The biological value of a dietary protein is determined by two parameters: its amino acid profile and its digestibility. If a dietary protein contains all essential amino acids—meaning it is complete—and easily undergoes enzymatic hydrolysis in the intestines, its biological value is maximal. Proteins of animal origin—such as eggs, meat, and fish—have a high biological value, which is set at a baseline of 100 units, whereas proteins from plant sources—such as potatoes, corn, white bread, and vegetables—have a lower biological value: 67, 36, and 30 units, respectively. They lack several essential amino acids, particularly Tryptophan and Lysine.

For normal Protein Synthesis in the human body, all essential amino acids must be supplied simultaneously, as they are not stored in the body. Therefore, protein nutrition must be complete. If consuming animal proteins is not possible, plant proteins containing different amino acids must be combined.

A failure to supply the body with specific essential amino acids disrupts the synthesis of structural and enzymatic proteins or hormones, leading to a decreased rate or even cessation of growth, self-renewal, and recovery processes, as well as a reduction in body mass and, consequently, overall physical performance.

Protein Intake and Its Impact on Physical Performance. The amount of protein consumed depends on sex, body weight, and the intensity of work performed. The protein intake recommendations established by the WHO for the adult population, which fully meet their requirements, are 0.8 g ⋅ kg^-1 of body weight per day, and 1 g ⋅ kg^-1 for children and adolescents. Consequently, for a 70 kg man, this standard amounts to 56 g of protein per day, and for a 55 kg woman, 44 g. These amounts provide 10–12% of total energy intake. However, other recommendations exist, according to which protein intake for an adult should be at least 1.5 g ⋅ kg^-1 ⋅ day^-1.

For athletes specializing in endurance sports, the protein requirement is 1–1.8 g ⋅ kg^-1 ⋅ day^-1. According to some data, during prolonged muscular activity, the protein requirements of highly trained athletes should not drop below 1.5 g ⋅ kg^-1 ⋅ day^-1, as only this level maintains a positive nitrogen balance in the athlete's body.

For athletes in strength sports, additional protein intake is necessary to increase muscle mass during training. Protein intake recommendations vary widely across different guidelines. On average, the protein requirement for endurance athletes performing low-volume and low-intensity physical loads, depending on energy expenditure, is 1.3–1.8 g ⋅ kg^-1 ⋅ day^-1, for high training loads it is 2 g ⋅ kg^-1 ⋅ day^-1, and for weightlifters and bodybuilders, it reaches 3 g ⋅ kg^-1 ⋅ day^-1. The total daily requirement for a track runner is within 90–105 g ⋅ day^-1, while for a weightlifter, it is 250 g ⋅ day^-1 (Table 47).

Excessive Dietary Protein Intake (exceeding 2.5 g ⋅ kg^-1 for sedentary individuals and 5 g ⋅ kg^-1 for athletes) overloads the gastrointestinal tract, causes putrefaction in the Large Intestine, and leads to the accumulation of under-oxidized and End products of Protein metabolism in tissues, which alters the body's acid-base balance and hinders peak athletic performance.

When dietary protein is insufficient, tissue redistribution of proteins occurs, drawing proteins from the liver, Blood Plasma, and muscles to supply the brain and heart. An inadequate supply of complete protein is particularly dangerous for children: it leads to delayed growth and development, anemia, and impaired Water-Salt Metabolism, which can be fatal.

Protein requirements should be met through foods containing complete proteins (low-fat milk and meat, eggs, fish). Numerous protein supplements are expensive and offer no significant advantages over natural foods, except for the fact that a large amount of protein is delivered in a small food volume, which is crucial for weightlifters and bodybuilders.

TABLE 47. Recommended Protein Intake for Athletes

The Role of Vitamins in Muscle Activity

The involvement of individual vitamins in Metabolic Regulation was discussed in Chapter 7. Under conditions of muscular activity, vitamins play a crucial regulatory role by ensuring a high rate of metabolic and oxidative processes associated with energy production mechanisms, protein and carbohydrate Biosynthesis, Lipid Peroxidation, Mineral Metabolism, and more. Therefore, an inadequate supply of specific vitamins to an athlete's body leads to decreased physical performance, impairing both anaerobic and aerobic energetic capacities.

There is a prevailing view that the daily Vitamin Requirements of athletes in certain sports are significantly elevated compared to sedentary individuals. This is due to the high energy expenditure of athletes during physical exertion, which can reach 5,000 kcal ⋅ day^-1 or more, as well as an increased rate of vitamin metabolism. In such cases, to maintain the physiological levels of vitamins, intake guidelines may exceed recommended values by 2–3 times. Replenishing vitamins during heavy physical loads is possible only through a varied diet and the additional intake of multivitamin complexes. However, consuming large quantities of vitamins—5 to 10 times the recommended daily allowance—does not positively impact athletic performance and, in some cases, can cause adverse health conditions (especially fat-soluble vitamins).

Depending on the dietary focus and the specific nature of muscular activity in various sports, the consumption of different vitamins is recommended. For instance, endurance sports primarily utilize vitamins that facilitate carbohydrate assimilation and oxygen utilization (B₁, B₃, C, E); speed-strength sports favor vitamins with anabolic effects or those that enhance protein synthesis (B₂, B₆, B₁₂, C, E); while marksmanship, biathlon, and auto racing preparation focus on vitamin A, which regulates visual processes. It has been established that certain vitamins must be supplied to the body in a balanced manner. Excessive intake of one vitamin increases the demand for others. If this demand is not met, hypo- or avitaminosis may occur. For example, consuming vitamin A increases the body's need for vitamins C and B₁, while vitamin B₁ increases The Need for Vitamin PP. Consequently, multivitamin complexes have been developed and are widely used to specifically balance individual vitamins. These include Aerovit, Decamevit, Undevit, Gendevit, Penghexavit, Ascorutin, Revit, Pentavit, Hexavit, Glutamevit, and many others. They are indispensable during heavy physical and neuro-emotional stress (especially during competitive periods), as well as under conditions of low or high ambient temperatures. The use of these preparations improves energy processes, cardiac contractility, and helps the body adapt to physical loads.

To enhance the efficacy of vitamins, numerous multivitamin complexes containing Trace Elements have been formulated (Vitrum, Unicap, Triovit, Manevit, Oligovit, Complevit, Glutamevit, etc.). The combination of multivitamins and minerals has a positive effect on metabolism, improving tolerance to training loads and enhancing athletic performance.

Additional vitamin supplementation should be pursued not only during intensive training and crucial competitions, but also in late winter and spring, when the vitamin content in food products declines. Only a consistently balanced diet rich in VITAMINS AND MINERALS allows an athlete to improve performance without health complications over years of training.

The Role of Minerals in Athletes' Diets

Athletes exhibit an increased demand for various minerals—particularly phosphorus, calcium, potassium, and iron—which are intensively excreted from the body during muscular activity. For instance, inorganic phosphate is essential for the resynthesis of high-energy phosphate compounds during recovery periods and for the replenishment of salts in Bone tissue. Therefore, the diet must include phosphorus-rich foods, with the highest amounts found in fish and eggs. Additional intake can be provided by glycerophosphate, lecithin, sodium phosphates, etc.

Calcium is involved in Muscle contraction and bone tissue formation, and it enhances phosphorus absorption. Therefore, calcium should be ingested in a 1:1.5 ratio with phosphorus. The primary sources of calcium are milk and cottage cheese.

During intense muscular activity, potassium losses can occur, causing alterations in the Functions of the heart muscle, Nervous system, and other Organs. Consequently, it must be supplied to the athlete's body in greater quantities than for non-athletes. The Main sources of potassium are potatoes, raisins, and dried apricots.

Training can disrupt iron metabolism and its assimilation by the body. Inadequate iron intake, poor absorption—especially from plant-based sources (where only 1–3% is absorbed)—can lead to the development of anemia, a sharp drop in blood Hemoglobin levels, particularly in female athletes. Iron deficiency negatively affects athletic performance, especially in endurance sports, as well as recovery processes.

To cover the daily iron requirement (1.5–2 mg), a 10-fold intake is necessary due to absorption difficulties. The most valuable sources of iron are animal products, such as liver and red meat. Excessive iron intake impairs zinc absorption and increases the risk of cancer and Heart Failure.

To ensure an adequate supply of all essential minerals for the body, the diet should include a generous amount of vegetables and fruits. Additional intake can be achieved through mineral water or multivitamin complexes.

Athletes experience an increased demand for water, especially during training in hot, dry weather, in strong airflow conditions (such as running), or with excessive salt intake. Water must be supplied to the body in the required amounts. Fluids should be consumed frequently, but in small portions.