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403
Foods and Raw Materials, 2018, vol. 6, no. 2 ISSN 2308-4057 (Print)
ISSN 2310-9599 (Online)
Review Article DOI: http://doi.org/10.21603/2308-4057-2018-2-403-412
Open Access Available online at http:jfrm.ru
Sport nutrition: the role of macronutrients
and minerals in endurance exercises
Rudolf Valenta and Yulia A. Dorofeeva
Medical University of Vienna,
Spitalgasse Str. 23, 1090 Vienna, Austria
* e-mail: -90julliet@gmail.com, rudolf.valenta@meduniwien.ac.at
Received June 1, 2017; Accepted in revised form August 2, 2018; Published December 20, 2018
Abstract: Athletes’ nutrition optimization is very important for the nutritional support in all sport specializations.
Macronutrients, as well as minerals and vitamins, are functionally active components that play an important role in
nutrition of athletes especially in endurance sport. Optimal use of diets, including specialized sport nutrition, normalizes
biochemical, immune, endocrine functions and restores athletes’ energy balance at different stages of sport exercises.
Non-optimal athletes’ nutrition of different age groups, inadequate to their physiological needs, and no personalized
approach to athletes’ diets, violate their right to adequate safe nutrition, according to international standards and criteria.
Nutritional factors are one of the most important key factors in the risk prevention measures for a large number of diet-
dependent diseases (e.g. digestive, liver, pancreas, cardiovascular system, endocrine system, and kidney diseases). The
review presents the information on energy requirements, balance and availability, types and content of functional
products for athletes. It also gives an overview of the specialized food market in Russia.
Keywords: Sport nutrition, minerals, proteins, energy, carbohydrates, specialized products
Please cite this article in press as: Valenta R. and Dorofeeva Yu.A. Sport nutrition: the role of macronutrients and minerals in
endurance exercises. Foods and Raw Materials, 2018, vol. 6, no. 2, pp. 403–412. DOI: http://doi.org/10.21603/2308-4057-2018-
2-403-412.
INTRODUCTION
Optimization of athletes’ nutrition, which takes into
account the phase state of the organism, athletes’
individual, age-sex and other features, is very important
for the nutritional support in all sport specializations. It
is of a great importance for athletes involved in
endurance sport, e.g. sportsmen of the world national
teams. Particular attention should be paid to young
athletes. A full-value optimal nutrition for all these
categories of athletes creates conditions for maximum
physical performance, increases a body's resistance to
stress and the effects of any unfavorable factors. Control
over the adequacy of nutrition, as well as its
optimization, is included in the structure of the
mandatory athletes’ check-ups to ensure timely detection
of health and fitness dynamics. Nutritional disorders
significantly reduce the effectiveness of training
activities, especially in trauma and stress, and increase
the risk of pathology development. Along with other
factors, they may adversely affect the effectiveness and
duration of athletes’ professional activity.
The introduction of specialized sport nutrition into
the diet is crucially important in the medico-biological
support of highly skilled athletes. It contains additional
macronutrients as well as essential micronutrients, such
as vitamins, minerals and other biologically active
substances. There are different types of sport nutrition:
foods and beverages containing high concentrations
of different types of carbohydrates for creating and
maintaining the glycogen in muscles for providing
energy;
protein enriched products for enhancing protein
synthesis in muscles and adapting to exercises;
multiple micronutrients (vitamins, minerals,
biologically active substances) in different forms; and
isotonic solutions for rehydration, additional energy
supply and etc.
RESULTS AND DISCUSSION
Energy requirements, energy balance, and energy
availability. An athlete’s energy requirements depend
on sport, the training period, competition cycle, and
recovery period. It varies from day to day depending on
changes in training volume and intensity level. It is well-
known that energy consumption is directly proportional
to the athletes’ physical activity. Therefore, people
involved in general fitness programs (for example,
exercises for 30 to 40 minutes a day, 3 times a week) can
usually meet energy needs, using regular foods in
accordance with a normal diet. Their energy
consumption can be in the range 1,800–2,400 kcal/day
or about 25–35 kcal/kg per day [1, 2]. Athletes who have
a moderate level of training (for example, 2–3 hours a
day of training, 5–6 times a week) or a high intensity of
Valenta R. et al. Foods and Raw Materials, 2018, vol. 6, no. 2, pp. 403–412
404
training (3–6 hours per day of intensive training for
5–6 days a week) may additionally have energy
consumption of 600 to 1,200 kcal or more per hour
during a workout [1, 2]. For elite athletes energy
consumption during endurance training or a competition
can be huge, e.g. the estimated energy expenditure for
cyclists participating in the Tour de France was
12,000 kcal per day [3, 4]. In addition, the requirement
for calories for athletes with significant body weight
(e.g., 100–150 kg) can range from 6,000 to 12,000 kcal
per day, depending on the volume and intensity of
various training skills [3]. That is why the only way to
optimize the athletes’ nutrition is the mandatory use of
specialized products and dietary supplements. The
violation of nutritional status, especially in highly
qualified athletes with extreme physical activity, has a
significant negative impact on health indicators. It is a
serious risk factor for the development of many diet-
dependent diseases which may be prevented by diet
regulation.
Energy consumption in sports can be calculated in
accordance with the recommendations, e.g., of the
American College of Sports Medicine [5]. Energy
balance occurs when total energy intake (EI) equals
total energy expenditure (TEE), which in turn consists
of the summation of basal metabolic rate (BMR), the
thermic effect of food (TEF), and the thermic effect of
activity (TEA).
TEE = BMR + TEF + TEA
TEA = Planned Exercise Expenditure +
+ Spontaneous Physical Activity + Nonexercise
Activity Thermogenesis
Below is the example of calculating of the energy
availability (EA) for a sportsman with body weight of
60 kg, body fat 20%, FFM 80% (= 48.0 kg FFM), EI
2,400 kcal/day, and additional energy expenditure from
exercise – 500 kcal/day:
EA = (EI – EEE) / FFM = (2,400 – 500) kcal /
/48.0 kg = 39.6 kcal/kg FFM
One should also take into account the peculiarities
of the three types of energy production, which differ
drastically:
– aerobic energy production, which is typical of sports
that require endurance exercises (marathon, skiing,
road racing, etc.);
– anaerobic energy production, i.e. the ability to
perform muscular work in conditions of oxygen
deficiency, which is realized mainly in sports that
require short-term energy release (weightlifting,
sprinting, etc.); and
– mixed anaerobic-aerobic energy production, which is
typical of sports with different alternating exercises
(combat sports, game sports, etc.)
Specialized foods that include easily recyclable
energy sources, micronutrients and biologically active
substances allow regulating and activating the main
functional processes (biochemical, immune, cardiac,
endocrine etc.) at various stages of the training process.
At the same time, the unbalanced athletes’
nutrition, inadequate to their physiological needs, the
lack of a personalized approach to athletes’ diets
violate their right to adequate safe food, according to
international standards and criteria (Resolution number
2001/25 of April 20, 2001, the human rights mission of
the United Nations).
History of sports nutrition. Sports nutrition is the
application of basic nutritional principles to improve
the training process, athletic performance and recovery
of athletes in post-training periods.
It is believed that the first evidence-based research
on athletic nutrition is closely related to the studies of
carbohydrate and fat metabolism, conducted in Sweden
in the late 1930s. In the late 1960s, Scandinavian
scientists began to study the processes of storing,
consuming and re-synthesizing glycogen in muscles
during long-term sports training. Technologies for
assessing the response of human tissues to physical
activity were also developed. Later, in 1965, the
scientific advances gave an opportunity to a group of
researchers at the University of Florida, led by Dr.
Robert Cade, to develop and scientifically prove the
possibility of using a carbohydrate-containing beverage
in sports. Thus, in 1965 the Gatorade appeared – one
of the first well-known sport drinks.
In the 1970s, physiologists from all over the world,
including the leading scientists of the Soviet Union,
began to develop a new direction – the physiology of
sports. These studies were carried out mainly in highly
skilled athletes, especially in long-distance runners as
these athletes developed the fastest and most life-
threatening depletion of glycogen stores in the muscles.
In addition, this sport was easily modeled in
laboratories with the use of treadmills and exercise
bikes. In this regard, much of the initial research of
sports nutrition has been associated with the study of
carbohydrate-containing foods.
Many studies in this area were empirical and
largely subjective, primarily related to the use of
protein products by body builders. Despite a large
number of studies on the use of protein products in
sports, many fundamental questions about the quantity,
quality and timing of protein intake remained
unrevealed. Despite the recommendations for optimal
protein intake in different sports and for athletes of
different ages, many aspects of this problem remained
controversial.
In the 1980s, physiological research ultimately
contributed to the research conducted by sport
physiologists and nutritionists. This was a necessary
step, since many aspects of nutrition in sports laid in
the plane of dietetics. Physiologists, on the basis of
studies by marathon runners and cyclists for long
distances, determined the need for consumption of
about 8 g of carbohydrates per 1 kg of body weight.
But it was nutritionists’ domain of competence to
determine which drinks, foods, and carbohydrates
athletes should to use in their diet to maintain the
balance.
Thus, in the 1980s sports nutrition appeared as a
new direction in the nutrition science. Taking into
account the importance of sports nutrition products in
maintaining high sports results, a significant part of the
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405
research was aimed at increasing the endurance of
athletes when using sports nutrition products.
By the 1990s, educational programs in many
countries appeared not only in sports medicine but also
in sports nutrition. They were developed not only for
dietitians, but for athletes and coaches.
Winter Olympics ‘Sochi-2014’ played a special
catalytic role in the development of research and
educational programs, expanding the range of sports
and technology of food production. The event revealed
the problem and forced further studies.
Types of specialized products for athletes. The
need to use specialized sport nutrition is due to the fact
that during training a large volume and high intensity
recovery efficiency and basic metabolic functions
cannot be accomplished with traditional foods and
diets.
In this regard, in the athletes’ diets, especially those
with high physical activity, various ‘specialized foods
for athletes’, or ‘sports nutrition’, are introduced.
In accordance with the official regulatory acts No.
1414 of the Ministry of Sports of the Russian
Federation, there are following types of sports
nutrition:
– carbohydrate (energy) drinks with high concentration
of carbohydrates;
– sport/rehydration drinks (isotonic solutions);
– non-liquid carbohydrate nutrition;
– natural proteins of animal and plant origin (animal
meat, fish, dairy – casein and whey proteins, egg white,
soy protein);
– hydrolyzed proteins with different degree of the
hydrolysis (mixture of peptides of different structure
and amino acids);
– individual amino acids or mixtures of 2 to 3 amino
acids;
– product for body weight control; complexes of
vitamins and mineral supplements;
– sports dietary supplements – individual compositions
of protein and non-protein nature that activate
biochemical processes (carnitine, creatine, succinate,
ribose, etc.); and
– additives for recovery after intensive workloads and
injuries.
By the effect on metabolism, special nutrients in
sports nutrition products are divided into the following
groups:
– with metabolic action, i.e. aimed at stimulating the
processes of anaerobic and aerobic metabolism;
– with anabolic action, i.e. enhancing the processes of
synthesis of substances in the body;
– used to maintain the biochemical homeostasis of the
body; and
– aimed at accelerating recovery processes after
physical training with antioxidant and antihypoxic
effect.
Market of specialized products for athletes in
the Russian Federation. At present, in the Russian
market there is a large number of specialized food
products for athletes (SFPA) with different ingredients
that can be characterized both by their ‘basic’
component and by the intended purpose.
The greatest demand on the sports nutrition market
is for protein (59%), followed by vitamins and minerals
(50%), amino acids (48%), creatine (38%), energy
(30%), and gainers (18%).
The sports nutrition market is rapidly growing. In
2013 it exceeded 1.3 billion rbls. It is more than 70%
higher than in 2012. According to IndexBox, the
supply in the Russian market of sports nutrition in 2012
was 40% higher than in 2011. The high growth rate of
the sports nutrition market was also observed in
2010–2011 (142% and 148% respectively) and
extremely high during 2014 Winter Olympics in Sochi.
According to the Discovery Research Group
agency, more than 90% of goods at the present sports
nutrition market in Russia is occupied by foreign
products. The volume of imported goods in value terms
following the results of 2012 amounted to more than
1.7 billion rbls., by the end of 2013 – more than
2.0 billion rbls. The protein compositions were more
than 40% of the total SFPA and about 17% is creatine-
containing SFPA. The analysis shows that most
Russian consumers prefer foreign-made goods. Only
13% of consumers choose sports foods of domestic
production.
In the end of 2015, the United States became the
undisputed leader in the supply of sports nutrition,
accounting for 70% of the total import volume. The
production of Germany accounted for about 18% of the
sports nutrition supplied to the Russian market.
Products from Canada, which accounted for about 7%
of all supplies, took the third place.
The analysis of specialized products for athlete
nutrition held at the Federal Center of Nutrition and
Biotechnology (Moscow) showed that over the period
2011–2016, more than 1000 SFPA of various
composition and different food and energy values were
submitted for examination. Protein and protein-
carbohydrate products were most popular, followed by
carbohydrate enriched with biologically active
substances, crystalline amino acids and their mixtures,
isotonic drinks, carbohydrate-mineral complexes with or
without vitamins, as well as vitamin and mineral
complexes and their combinations. For the last years, the
number of biologically active substances of plant origin,
mostly from Asian countries, as well as supplements that
are used mainly for the nutrition of athletes (creatine and
L-carnitine in the form of various compounds, carnosine,
lipoic acid, hydroxymethylbutyrate, etc.) has increased
dramatically.
About 60% of products are based on concentrates
and isolates of whey proteins and about 15–20% –on
amino acids. L-carnitine, creatine, glutamine, HMB
(hydroxymethylbutyrate), glucosamine, chondroitin,
leucine, and arginine are used more often.
Recently, the products of sports nutrition (mainly of
foreign origin) contain such new ingredients as
hydroxyisocaproic acid (HICA), agmatin, β-alanine,
and norvaline.
As for protein-containing products, two types are
represented in the market:
– concentrated protein, which consists of 70–90%
protein in the form of a monocomponent without or
with additives in different compositions with vitamins,
minerals, creatine, individual amino acids, digestive
enzymes, plant extracts, etc.;
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406
– carbohydrate-protein containing 18–35% protein with
or without similar additives.
The most popular ones and often found in the
SFPA are:
– milk proteins;
– combination of whey proteins with egg albumin;
– combination of whey and soy proteins;
– meat proteins;
– soy proteins per se;
– proteins of peas;
– collagen hydrolyzates; and
– proteins of plant origin.
Whey proteins are the most commonly used source
of protein. They are used as whole and hydrolyzed
proteins. Caseins and their salts in the form of
caseinates, both as mono-components and as mixtures
of these whey protein fractions, are also popular
among athletes.
A protein component in the products imported into
the Russian Federation and recently undergoing
research is almost always represented by whey proteins
or their mixture with casein or chicken egg protein.
Attention is drawn to the fact that there is practically
no soy both in foreign products and those
manufactured in the Russian Federation. This fact is
apparently explained by the active anti-advertising in
Russia on soy due to its genetically modified forms.
In a number of products, hydrolyzed collagen
(usually with milk and egg protein) is present as an
integral part of the protein base. At the same time, a
limited amount of protein products is made on the basis
of pure collagen (hydrolyzate), usually with the
addition of vitamin and mineral complexes, and is
advertised as a source of individual components to
maintain the functions of the skeletal muscles.
A sufficiently large segment in the total amount of
sports nutrition products is taken by mixtures of
crystalline amino acids, which come in the form of
capsules, tablets, and in liquid form. A pure BCAA
(a mixture of branched amino acids) is the most
popular, while BCAA with other components,
including various amino acids and vitamins, takes a
second place, and a complex of essential and non-
essential amino acids comes next. In some cases, as a
source of amino acids, products are declared in the
form of hydrolysates of milk, whey proteins or
collagen.
The carbohydrate component in the products is
usually represented by corn maltodextrin and/or simple
carbohydrates (sucrose, fructose). The latter are often
the basis of liquid forms of products. Carbohydrate
products with vitamins and/or mineral components
make up the hypo- and isotonic group and are more
often present as ready-made beverages or liquid
concentrates that require additional dilution.
In addition to protein products, carbohydrate or
mixed basis with a high food and energy value, a
sufficient amount of products is made up of specialized
products that can equally be attributed to biologically
active additives to food, but designed to feed athletes:
creatine, glutamine, caffeine, taurine; carnitine,
glucosamine and chondroitin, omega-3 fatty acids,
vitamins and/or vitamins-mineral complexes, herbal
compositions and their extracts (guarana, ginseng,
ginkgo biloba, green tea, bearberry, garcinia etc.). The
listed components, with the exception of plants, are
usually offered both as mono-components (in the form
of powders, tablets, capsules), and in the form of
various combinations.
One of the trends observed in the last few years was
the presence of specialized products from abroad,
mainly from the USA, except for long-used creatine
monohydrate, amino acids in L-form, carnitine and
other components that are products of intermediate
metabolism in energy cycles or their substrates: lipoic
acid, alpha-ketogluthorate, ketogluthorates of amino
acids and esters of ketoforms of amino acids,
acetylated forms of amino acids, creatine compounds
in the form of taurine or ethyl ether yl or
hydroxymethylbutyrate, or other compounds (beta-
alanine, norvaline, agmatine, etc.). These components
are also produced as individual additives and are often
present in the composition of sports products in the
form of complexes not only in carbohydrate, but also in
carbohydrate-protein compositions.
Carbohydrates in the diet of athletes. It is known
that the consumption of carbohydrates is extremely
important for optimal adaptation to frequent stress
signals, which is typical of sports. Adequate and timely
intake of carbohydrates is one of the key factors for the
recovery of glycogen, the work of muscles and liver [6].
With increasing of physical exercise activity, the
total demand for carbohydrates increases significantly.
At endurance sports, the daily requirement for
carbohydrates is 5–8 g per 1 kg of body weight [7].
Carbohydrates are the key energy factor for both
aerobic and anaerobic pathways of metabolism, the
main nutrients for muscle contraction during physical
exercises of varying intensity. The degree of use and
depletion of carbohydrates accumulated in muscles is
different for different sports and largely depends on the
duration and intensity of the training process, as well as
the degree of hydration of the organism and, the
athletes’ level of training [8]. Along with this, the lack
of carbohydrates becomes a limiting factor for the
cognitive functions of athletes [9, 10].
The carbohydrate component in the products is
usually represented by corn maltodextrin and/or simple
carbohydrates (sucrose, fructose). The latter are often
the basis of liquid products.
One of the products of European origin is
amylopectin barley starch ‘Vitargo®’ (Sweden). The
chain length of its carbohydrates is 500,000–700,000
(carbohydrate chain length of starch-like foods is more
than 2.5 х 108 D, maltodextrin – 1,000–10,000 D,
dextrose – 180 D). Besides, it is characterized by low
osmolality in comparison with other carbohydrates.
The molecular structure of the carbohydrate resembles
glycogen, which ensures its rapid entry into the blood.
Clinical trials have shown it to be significantly more
effective than dextrose and maltodextrin. Carbohydrate
products with vitamins and/or mineral components
constitute a group of hypo- and isotonic agents.
It should be noted that different carbohydrates
differ in glycemic index (food rating depending on the
response of blood glucose to reference food)
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407
and are accordingly applied for different phases of
training, competitive, and recovery processes.
Glycemic index of sucrose is 65, fructose – 23,
glucose – 100, and maltodextrin – 96.
Given the significant differences in the properties
and types of carbohydrates used in sports practice,
glycemic index (GI) is extremely important criteria for
their usage in different periods of the sports process. It
is used to characterize the rate of carbohydrate to
glucose conversion in blood using the concept of
glycemic index. GI ranks all products in relation to
glucose, less often – white bread. The glycemic index
is determined by the rate of a given carbohydrate (or
product) causing an increase in blood sugar levels.
Glucose has a high glycemic index, sucrose –
moderate, fructose – low.
Foods with a high GI provide a rapid increase in
blood sugar levels. Carbohydrates contained in the
relevant products are easily digested and absorbed by
the body; they are quickly used to produce energy and
glycogen. Foods with a high glycemic index are best
used immediately before or immediately after training.
When using products with a low glycemic index, the
blood sugar level increases more slowly.
Carbohydrates from such foods are not acquired
immediately, but provide a more lasting effect, so it is
more appropriate to use it at least 1.5–2.0 hours before
training.
There are special features when using the form of
carbohydrates, e.g., combined carbonated drinks used
in sports. One of the criteria for assessing the
tolerability, and absorption of specialized foods is
osmolality, which characterizes the osmotic pressure of
liquids and is the sum of cations, anions, and non-
electrolytes, i.e. of all kinetically active particles in 1 l
of water (or 1 kg of water) and is expressed in MMol
per liter (mOsm/l) or MMol per kg (mOsm/kg).
In accordance with the medical and biological
requirements for carbohydrate-mineral drinks intended
to overcome the effects of dehydration and loss of
electrolytes during training and competitions, their
osmolality should be in the range of 200–330 mOsm/kg,
preferably 270–330 mOsm/kg.
Carbohydrates make a significant contribution to
the osmolarity of ready-made beverages. The degree of
degradation of complex carbohydrates affects this
index of the product, while mono- and disaccharides
increase it. Mineral salts being used for replenishment
of electrolyte losses also contribute to the osmolarity of
beverages.
In this regard, to optimize the carbohydrate-mineral
composition of the products being developed, studies
have been carried out to determine the osmolarity of
solutions of carbohydrates and mineral salts, which, as
a rule, form part of hypo- and isotonic drinks. Glucose
and fructose, related to monosaccharides, have a high
osmolarity, and its values increase directly in
proportion to the concentration of solutions. Thus, 6%
solutions of glucose and fructose have osmolarity of
309 and 341 mOsm/l, and the sugar solution of this
concentration has an osmolality of 180 mOsm/l. The
smallest osmolality is represented by solutions of
maltodextrins (dextrose equivalent value of 18.9%): a
20% solution has an osmolality of 200 mOsm/l. In this
regard, for the preparation of an isotonic beverage, it is
necessary to use several carbohydrate components in
ratios, which would provide both the optimal
osmolarity and the content of carbohydrates required
for the restoration of the organism.
To prepare beverages for the replenishment of the
body with carbohydrates and salts, various
concentrations of salt-electrolyte solutions are
introduced into their formulation: calcium lactate,
magnesium citrate, potassium citrate, and citrate and
sodium chloride, which affect the osmolarity of drinks.
Osmolarity of solutions of all salts should be in a direct
proportion to their concentration [11].
The principles and strategies for carbohydrates intake
in different phases of the training process are presented
in Table 1. The data are from [12].
Proteins in the diet of athletes. Proteins are the
main ‘building’ material of the body. They are part of
the muscles, ligaments, skin, and internal organs, used
as an energy source (1 g of protein ideally gives
4.46 kcal, however, given the cost of digestion, this
figure decreases to about 3 kcal).
The protein of the food hydrolyses into the amino
acids, which are then used as a ‘building material’ for
body proteins. Therefore, the amino acid composition
of the protein is of great importance, especially leucine,
isoleucine, and valine. They are a kind of basis around
which the entire metabolism of proteins is built. The
proteins of milk, meat, and eggs are optimal in
nutrition. Meat is rich in glutamine, eggs in
methionine. The most balanced composition of the
whey protein is cow milk protein (lactoalbumin) and
protein contained in egg yolk. Besides, milk contains
casein, which is less valuable as a food protein, but not
much. Egg protein (albumin) is also a very valuable
component of food. Protein-rich foods are eggs,
chicken, turkey, cottage cheese, cheese, yoghurt, kefir,
milk, lean beef, fish, beans (peas, beans, lentils), and
nuts. The assimilation of proteins is essentially related
to its structure. Milk and egg proteins, which are in
solution in the form of separate molecules ‘rolled up
into tangles’, are absorbed quite well. However, when
we get cottage cheese from milk or cook eggs, a
process of protein denaturation takes place, in which
some of the bonds in the protein molecules are broken,
especially the sulfide bridges and weak bonds between
some amino acid residues. At the same time, their
assimilation becomes more complicated. On the
contrary, proteins contained in meat foods, when heat-
treated, become more easily assimilated, although their
nutritional value decreases. Soy proteins, which have
high biological value and good digestibility, are
optimal. Proteins of leguminous plants are better
absorbed after a long treatment. Plant proteins are
mostly obtained from seeds, where the protein is stored
as a ‘building material’ for the future plant. The
proteins contained in mushrooms are undesirable,
because they are poorly absorbed by the body (because
of their fibrous structure, the presence of carbohydrate
residues, etc.).
Valenta R. et al. Foods and Raw Materials, 2018, vol. 6, no. 2, pp. 403–412
408
Table 1. Summary of guidelines for carbohydrate intake by athletes
Situation Carbohydrate targets Comments on type and timing of carbohydrate intake
Daily needs for fuel and recovery:
(1) The following targets are intended to provide high carbohydrate availability (i.e, to meet the carbohydrate needs of the muscle
and central nervous system) for different exercise loads for scenarios where it is important to exercise with high quality and/or at
high intensity. These general recommendations should be fine-tuned with individual consideration of total energy needs, specific
training needs, and feedback from training performance.
(2) On other occasions, when exercise quality or intensity is less important, it may be less important to achieve these carbohydrate
targets or to arrange carbohydrate intake over the day to optimize availability for specific sessions. In these cases, carbohydrate
intake may be chosen to suit energy goals, food preferences, or food availability.
(3) In some scenarios, when the focus is on enhancing the training stimulus or adaptive response, low carbohydrate availability may
be deliberately achieved by reducing total carbohydrate intake, or by manipulating carbohydrate intake related to training sessions
(e.g,, training in a fasted state or undertaking a second session of exercise without adequate opportunity for refuelling after the first
session).
Light – Low intensity or skill-based
activities
3–5 g/kg of athlete’s
body weight/d
– Timing of intake of carbohydrate over the day may be
manipulated to promote high carbohydrate availability
for a specific session by consuming carbohydrate
before or during the session, or during recovery from a
previous session
– Otherwise, as long as total fuel needs are provided,
the pattern of intake may simply be guided by
convenience and individual choice
– Athletes should choose nutrient-rich carbohydrate
sources to allow overall nutrient needs to be met
Moderate – Moderate exercise program
(e.g., ∼1 h/d)
5–7 g/kg/d
High – Endurance program
(e.g., 1–3 h/d moderate to high-
intensity exercise)
6–10 g/kg/d
Very high – Extreme commitment
(e.g., > 4–5 h/d moderate
to high-intensity exercise)
8–12 g/kg/d
Acute fueling strategies – These guidelines promote high carbohydrate availability
to promote optimal performance during competition or key training sessions
General
fueling up
– Preparation for events < 90 min
exercise
7–12 g/kg/24 h as for
daily fuel needs
– Athletes may choose carbohydrate-rich sources that
are low in fiber/residue and easily consumed to ensure
that fuel targets are met, and to meet goals for gut
comfort or lighter “racing weight”
Carbo-hydrate
loading
– Preparation for events > 90 min
of sustained/intermittent exercise
36–48 h of
10–12 g/kg body
weight/24 h
Speedy
refueling
– < 8 h recovery between
2 fuel-demanding sessions
1–1.2 g/kg/h for first
4 h then resume daily
fuel needs
– There may be benefits in consuming small, regular
snacks
– Carbohydrate-rich foods and drink may help to ensure
that fuel targets are met
Pre-event
fueling
– Before exercise > 60 min 1–4 g/kg consumed
1–4 h before exercise
– Timing, amount, and type of carbohydrate foods and
drinks should be chosen to suit the practical needs of
the event and individual preferences/experiences –
Choices high in fat/protein/fiber may need to be
avoided to reduce risk of gastrointestinal issues during
the event – Low glycemic index choices may provide a
more sustained source of fuel for situations where
carbohydrate cannot be consumed during exercise
During brief
exercise
– < 45 min Not needed
During
sustained high
intensity
exercise
– 45–75 min Small amounts,
including mouth rinse
– A range of drinks and sports products can provide
easily consumed carbohydrate
– The frequent contact of carbohydrate with the mouth
and oral cavity can stimulate parts of the brain and
central nervous system to enhance perceptions of well-
being and increase self-chosen work outputs
During
endurance
exercise,
including
“stop and
start” sports
– 1–2.5 h 30–60 g/h – Carbohydrate intake provides a source of fuel for the
muscles to supplement endogenous stores
– Opportunities to consume foods and drinks vary
according to the rules and nature of each sport
– A range of everyday dietary choices and specialized
sports products ranging in form from liquid to solid
may be useful
– The athlete should practice to find a refuelling plan
that suits his or her individual goals, including
hydration needs and gut comfort
During ultra-
endurance
exercise
– > 2.5–3 h Up to 90 g/h – As above
– Higher intakes of carbohydrate are associated with
better performance
– Products providing multiple transportable
carbohydrates (Glucose:fructose mixtures) achieve high
rates of oxidation of carbohydrate consumed during
exercise
Valenta R. et al. Foods and Raw Materials, 2018, vol. 6, no. 2, pp. 403–412
409
The ‘ideal’ protein contains 40 mg of isoleucine, 70
mg of leucine, 55 mg of lysine, 35 mg of methionine
and cystine (in total), 60 mg of phenylalanine and
tyrosine (in total), 10 mg of tryptophane, 40 mg of
threonine, and 50 mg of valine (in 1 g).
Using the composition of the ‘ideal’ protein, one
can calculate the content of essential amino acids in a
given protein relative to the ideal one. This criterion is
then used to assess the balance of the diet. Analysis of
this indicator immediately reveals what amino acids
will be missing in nutrition. For example, if the food
lacks sulfur-containing amino acids, you can
supplement the diet with egg whites. It should be noted
that exercises impose requirements on the quality of
the protein, and even interchangeable amino acids must
come from food in sufficient quantities.
The indicator of the biological value of the protein
(BV) is ‘the amount of protein stored by the body when
eating 100 grams of this protein food’. For the whey
protein of cow milk (lactoalbumin, albumin) BV is
almost equal to 100, for casein and soy proteins – 75,
and for proteins of meat and fish – 80. For most
vegetable protein BV is approaching 50. The exception
is the protein contained in potato and nuts. The thermal
processing of food leads to a drop in the biological
value of the protein, but it is necessary, and not only
because of the organoleptic properties of food: eating
cheese, eggs, for example, can lead to salmonellosis,
and raw milk – to intestinal disorders.
Another widely used criterion is the protein
efficiency index (PEI). It is determined by the effect of
this protein on muscle growth. Performance indicators
for different proteins are also different, but here again
whey protein remains the leader. The balance of amino
acids and the optimal chemical structure are the most
important characteristics of the protein.
The newest criterion for the quality of the consumed
protein is the amino acid-adjusted digestibility index
(PDCAAS). However, it does not take into account the
significant difference in the nutritional value of proteins
from different sources. Soy protein, caseinate, and egg
white are the leaders – 1 (compare: beef – 0.92,
peas – 0.69, canned beans – 0.68, oats – 0.8, canned
lentils – 0.2, peanuts – 0.52, wheat –0.40, whole wheat
gluten – 0.25).
Dietary protein during a workout acts as a trigger
and substrate for the synthesis of contractile muscle
fibers and metabolic proteins, and also contributes to
structural changes in the ligament apparatus and bone
tissue of athletes [13, 14]. Studies show that
stimulation of the synthesis of muscle proteins in
response to even a single sports load occurs for at least
24 hours, with an increase in sensitivity to the inclusion
of dietary proteins in muscle tissue [15].
It is widely believed that the requirements for high
physical loads in the protein are increased. It is
believed that to increase endurance, it is necessary to
compensate for the consumption of muscle protein
consumed by oxidative processes. To increase strength,
it is useful to give extra protein in order to build muscle
mass (the so-called anabolic effect). At the same time,
convincing scientific findings confirming these
provisions have not been obtained at present (unlike
the additional intake of carbohydrates, for which the
effect of increasing stamina is a strictly proven fact).
Moreover, giving hypothetical assumptions about the
benefits of additional amounts of protein, one cannot
ignore the obvious negative effects of its overdose,
which can begin with a dose of 2–4 g of protein per 1
kg of body weight.
It is now established that, at high physical
exercises, despite the increase in energy consumption,
the need for protein does not increase very much. An
adult who leads an average lifestyle should receive 11–
12 % of the daily calorie intake from proteins (both
animal and plant ones, approximately in equal
proportions). In intensively trained athletes under
certain conditions, the quota of protein intake can be
slightly increased in comparison with these indicators.
A special role in the diet of athletes of any age and
sports qualifications is given to protein products.
Maintaining a balance between the synthesis,
breakdown and re-synthesis of protein is the basis of
physiological adaptation of athlete's muscles to
stresses. The recommended protein intake for athletes
varies from 1.2 to 2.0 g/kg per day. It is important to
control not only the lack of protein in the diet, but also
its excess, which affects not only the athletic
performance, but also the safety for the body of
athletes, especially young ones. Excessive consumption
of protein can lead to osteoporosis, impaired renal
function, and other pathologies.
The problem of protein dosing in athletes is still the
subject of debates. One thing is clear that protein intake
beyond these standards does not increase adaptation to
the load [16].
It is now generally accepted that protein intake in
the amount of 1.2–1.6 g/kg body weight per day
provides the optimal amount of amino acids for
growth, maintenance, and recovery of all tissues
provided adequate calorie intake. In particular, it was
shown that in actively trained cyclists (with more than
5900 kcal diurnal energy consumption), a positive
balance of nitrogen is observed when the protein is
consumed at 1.4 g/kg body weight, which is only
20–40% higher than the protein requirement among
people who lead an average lifestyle [17, 18].
Studies have shown that protein synthesis in
muscles is gradually optimized depending on physical
loads by assimilating proteins with high biological
value. Approximately 10 g of essential amino acids are
included in the re-synthesis in the muscle tissue already
in the early recovery period [14, 18], which is
transformed into a recommended protein intake equal
to 0.25–0.3 g/kg body weight or 15–25 grams per
average weight of the athlete (60–80 kg). Higher doses
of protein (e.g., > 40 g of dietary protein) do not have
much effect and can be significant only for athletes
with a large body weight or when weight loss is
required [19].
The proportion of proteins of animal origin should
be at least 60%, which provides the desired optimum
Valenta R. et al. Foods and Raw Materials, 2018, vol. 6, no. 2, pp. 403–412
410
for the amino acid composition. The remaining
40% should account for proteins of plant origin. In
special cases, the proportion of animal proteins can be
80%: for example, during training, aimed at the
development of speed-strength qualities, as well as
increasing muscle mass, or performing long and
intense training loads.
Minerals in sport. Mineral substances contained in
food are extremely important for body’s life. Thus,
sodium is the main extracellular ion taking part in
water transfer, blood glucose, generation and
transmission of electrical nerve signals, and muscle
contraction. Potassium is the main intracellular ion that
takes part in the regulation of water, and acid and
electrolyte balance. Chlorine is necessary element for
the regulation of osmotic pressure, the formation of
gastric acid (chloride ions concentrate mainly in the
extracellular fluid).
With intensive training and increased sweating,
additional sodium intake (in the form of salt) is
recommended to prevent seizures. Excess sodium
negatively correlates with the calcium content. The
constancy of osmotic pressure and the constancy of the
volume of fluid are important interrelated processes of
the body. The change in the amount of salts in the body
(their retention or loss) is associated with the
corresponding compensatory changes in the volume of
the liquid. Sodium regulates fluid balance in the
intercellular space. Sodium ions are largely responsible
for the distribution of water in the body. Consequently,
the increase or decrease in sodium ions leads to a
proportional fluid retention or loss. The constancy of
the osmotic pressure is maintained by changing the
volume of the liquid. Sodium also participates in the
transport of amino acids, sugars, and potassium.
Most products, such as cheese, bread, meat
products, fish, vegetables, and canned foods contain
sodium chloride.
The main part of sodium and chlorine ions is
excreted from the body with urine, and with intensive
work, physical exertion, especially in conditions of
elevated ambient temperatures, with sweat. The
demand for sodium sharply increases during physical
exertion (long-distance running, marathon, etc.). In this
case, it is necessary to increase the amount of salt
consumed, taking into account the food content of up
to 20–25 g per day [20]. Sodium chloride is widely
used as an additive to food. The intake of sodium
chloride with food can fluctuate significantly. With
excessive consumption of sodium chloride in the body,
the liquid is retained. Increased salt intake is one of the
main risk factors for the development of arterial
hypertension [21], including in athletes.
At the same time, it should be noted, that to avoid
the risk of dehydration and reduce performance people,
who are engaged in heavy work or exertion, one should
use drinks containing carbohydrates and electrolytes
during and after physical activity. The use of dilute
solutions of carbohydrates and electrolytes (including
sodium chloride because of its loss with sweat) has a
more favorable effect on the recovery of the organism
under severe working conditions than the use of water
only [22, 23].
With short physical exertion, there is no need to
consume additional amounts of sodium. Evidently, the
compensation of the losses of this electrolyte acquires
in the course of prolonged heavy physical exertion, to
maintain its concentration in the blood plasma and the
osmotic pressure. Specialized food products, including
beverages, can be used.
The sodium concentration in such beverages varies
generally between 20 and 40 Mmol/l. The purpose of
adding this electrolyte is not only to recover its
reserves. It pursues the goal of maintaining the volume
of extracellular fluid, increasing the rate of absorption
of water and glucose in the small intestine. Moreover,
the addition of sodium to the drink contributes to the
desire to drink, and this can increase the amount of
fluid consumed, which is favorable for maintaining the
volume of extracellular fluid [24, 25].
The inclusion of various carbohydrates in
beverages, including glucose, sucrose, and
maltodextrin, has certain advantages both in terms of
the rate of absorption of water and sugars, as well as in
improving the taste of the drink [26]. Taste sensations
play an important role, since they can affect the amount
of drink consumed.
Thus, with heavy physical exertion and unfavorable
environmental factors (high temperature), dilute
solutions remain the advantage. In most situations, a
carbohydrate concentration of 2–8% is recommended.
As noted above, in practice, mixtures of various
carbohydrates are often used, including free glucose,
sucrose, maltose, and maltodextrin.
The addition of fructose is permissible, but it is
worthwhile to avoid the use of high concentrations or
fructose alone, since fructose absorption is worse than
glucose, and, ultimately, high doses can lead to a risk
of diarrhea. Rehydration after physical exertion is an
important part of the recovery process. To compensate
for losses, it is recommended to use a volume of liquid
that exceeds by at least 50% its amount lost with
sweat [27]. In order to quickly restore the body's
resources, dilute solutions of glucose with the addition
of sodium chloride are used, since these hypotonic
solutions are most effective in reducing the retention in
the stomach and absorption in the intestine.
Replenishment of fluid loss in the body of athletes
should occur due to regular compliance with the
drinking regime. It is shown that the loss of 9–12% of
water is an emergency situation for the body and can
lead to death. Loss of 2% of weight due to water
reduces the workability by 3–7%, while with the loss
of 40% of protein, fat and carbohydrates, a person can
stay alive for a long time. In severe physical exertion it
is necessary to monitor the state of the water balance
and continuously replenish the fluid loss. Water comes
in with liquids and foods and as a result of metabolic
processes. The first way gives about 60% of the total
water consumption, the second one – 30% and the third
– about 10%. There are also different ways of
removing water from the body. 50–60% of water per
day is discharged with urine, about 20% - with exhaled
air, 15–20% with sweat (depending on the intensity of
exercise), and less than 5% – with feces. The average
person needs about two liters of water a day to make up
for the losses. With intensive loads, expenditure
Valenta R. et al. Foods and Raw Materials, 2018, vol. 6, no. 2, pp. 403–412
411
increases, reaching 3–4 l per day. It is proved that
when the volume of fluid in the body decreases by 2%,
the athlete's result may deteriorate by 15%.
Biochemical and physiological recovery of the
body begins immediately after physical activity. The
most efficient way to compensate for the loss of a large
amount of water and salts can be with the help of
weakly acidic and slightly sweet mineralized drinks,
and the hypo-and isotonic solutions of carbohydrate-
mineral complexes which are the most physiological.
CONCLUSION
Optimization of nutrition of athletes is very
important for the nutritional support in all sport
specializations. Macronutrients as well as minerals and
vitamins are functionally active components, especially
in endurance sport. Optimal uses of diets, including
specialized sport nutrition, improves biochemical,
immune, and endocrine body’s functions and restores
energy balance at different stages of sport exercises.
Nutritional factors are one of the most important key
factors in the risk prevention measures for a large
number of diet-dependent diseases (e.g. digestive,
liver, pancreas, cardiovascular system, endocrine
system, kidney diseases).
CONFLICT OF INTEREST
The authors declare no conflict of interest.
ACKNOWLEDGEMENTS
We are grateful to Prof. R. Khanferyan for the
assistance in the preparation of the article.
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ORCID IDs
Rudolf Valenta https://orcid.org/0000-0001-5944-3365
Yulia A. Dorofeeva https://orcid.org/0000-0003-4781-0185
