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Review Mayo-Agosto 2022;6(2):73-84
https://doi.org/10.33936/qkrcs.v6i2.4534
Facultad de Ciencias de la Salud. Universidad Técnica de Manabí. Portoviejo, Ecuador 73
Isotonic sports drinks: formulation and physiological effects of their consumption
Bebidas deportivas isotónicas: formulación y efectos fiosiológicos de su consumo
Yanelis Ruiz
1
* Mario A. García
2
Abstract
When practicing intense physical exercise for more than an hour, it is recommended to counteract the loss of
water and electrolytes and provide an energy substrate by drinking isotonic sports beverages. These contain
carbohydrates and mineral salts at the same osmotic pressure as blood, facilitating the rapid absorption of
their constituents. Its consumption before, during, and after prolonged physical exercise is more effective than
water in preventing dehydration, helping to maintain performance during exercise, delaying the onset of
fatigue, and accelerating recovery. Based on the demand for more natural foods, there is an interest from the
food industry to produce isotonic drinks from ingredients such as fruits, cereals, among others. In this sense,
this review describes some aspects of the formulation and physiological effects of consuming this type of drink.
Keywords: isotonic drink; electrolyte; osmolality.
Resumen
Al practicar ejercicio físico intenso durante más de una hora, se recomienda contrarrestar la pérdida de agua
y electrolitos y proporcionar un sustrato energético mediante el consumo de bebidas deportivas isotónicas.
Estas contienen carbohidratos y sales minerales a la misma presión osmótica que la sangre, facilitando la
rápida absorción de sus constituyentes. Se ha demostrado que su consumo antes, durante y después del
ejercicio físico duradero es más efectivo que el agua en la prevención de la deshidratación, ayuda a mantener
el rendimiento durante el ejercicio, retrasa la aparición de la fatiga y aceleran la recuperación. A partir de
la demanda de alimentos más naturales, existe un interés de la industria alimentaria por producir bebidas
isotónicas a partir de ingredientes como frutas, cereales, entre otros. En este sentido, en la presente revisión
se describen algunos aspectos sobre la formulación y efectos fisiológicos del consumo de este tipo de bebida.
Palabras clave: bebida isotónica; electrolito; osmolalidad.
*Dirección para correspondencia: yaneruiz1992@gmail.com
Artículo recibido el 24-03-2022 Artículo aceptado el 21-06-2022 Artículo publicado el 28-06-2022
Fundada 2016 Facultad de Ciencias de la Salud de la Universidad Técnica de Manabí, Ecuador.
Introduction
The water balance of the body at rest is maintained thanks to an adequate balance between the
inflows and outflows of fluids1. Nevertheless, when physical exercise is performed, lost fluids must
be replenished before symptoms of dehydration occur since it affects sports performance and
increases the risk of injury2.
Although when practicing physical exercise for less than an hour, it is enough to drink water before,
during, and after to maintain an adequate hydration, when the exercise is intense and long-lasting or
is practiced in a particularly hot environment, the body loses water and electrolytes rapidly through
sweat and increases energy consumption, with a consequent decrease in blood sugar concentration
and glycogen stores3. Therefore, during prolonged physical exercise, it is advisable to counteract the
loss of these substances by consuming isotonic sports drinks.
Thus, starting in the 1960s, at the University of Florida, a formula of carbohydrates, electrolytes,
and water was developed to improve the performance of a group of American football players and to
prevent dehydration caused by intense physical activity4.
1
Universidad de Chile, Facultad de Ciencias Químicas y Farmacéuticas, Máster en Ciencia y Tecnología de los Alimentos, Santiago de Chile, Chile,
yaneruiz1992@gmail.com, https://orcid.org/0000-0001-9889-322X
2
Universidad Técnica de Manabí, Facultad de Ciencias de la Salud, Doctor en Ciencias de los Alimentos, Departamento de Ciencias Biológicas, Portoviejo, Manab í,
Ecuador, mario.garcia@utm.edu.ec, https://orcid.org/0000-0002-0304-9665
Isotonic sports drinks: formulation and physiological effects of their consumption
Ruiz, García
74 Facultad de Ciencias de la Salud. Universidad Técnica de Manabí. Portoviejo, Ecuador
To date, the development of new formulations that are increasingly more effective and more widely
accepted by consumers has continued. This increase is mainly due to the increased competitiveness
in the market of the different brands, among the best known are Gatorade® (The Quaker Oats Co.),
Isostar® (Wander), Powerade® (Coca-Cola), and Aquarius® (Coca-Cola).
Commercial sports drinks usually contain ingredients such as preservatives, colorants, artificial
sweeteners, aromatizers, and flavorings, used to improve palatability and to prolong shelf life, but
they have been severely questioned for their potential harm to consumer health5. Based on the demand
for more natural drinks, there is an interest from the food industry to produce isotonic drinks from
fruits, cereals, and other natural ingredients. The use of these raw materials is advantageous, not only
because they add natural flavor and color, but also they provide vitamins, minerals, and antioxidant
substances that enrich the product nutritional profile. In this sense, this review describes some aspects
of the formulation and physiological effects of consuming this type of drink.
Requirements of water, carbohydrates, and electrolytes during the practice of physical exercise
Fatigue has been defined as the inability to maintain a given or expected force or power and is
unavoidable during intense exercise6. During the competition, the objective of nutritional strategies
is to improve performance, which is achieved by minimizing the influence of factors that cause
fatigue, which are hyperthermia, dehydration, depletion of carbohydrate stores, electrolyte imbalance,
and gastrointestinal discomfort7.
In healthy individuals, water is the largest component of the body. Its homeostasis is essential for
virtually all physiological functions. Therefore, it is of vital importance to replace the water lost
during the practice of physical exercise. Effective fluid replacement relies primarily on the ingestion
of appropriate beverages throughout the day. Thirst is implicated in water intake, although certain
behavioral habits also have an important influence on drinking. Sports drinks play an important role
in this regard, as their flavor profile encourages fluid intake, and their electrolyte content is crucial
for retention of ingested water8.
In general, the administration of carbohydrates and electrolytes is not considered necessary for
physical activity practiced for less than one hour, but in events of longer duration and to supply
energy, prevent dehydration and promote recovery after exercise, this kind of supplementation plays
a fundamental role3.
For the sustained practice of sports, energy must be provided in the form of carbohydrates. Its
addition to beverages consumed before, during, and after intense and prolonged exercise:
• Provides an energy substrate for the muscles. A substantial portion of the carbohydrates
ingested during exercise is available for oxidation, but there appears to be a maximum rate
(approximately 1 g/min) at which it can be oxidized, even when much larger amounts are
consumed9.
• Prevents the development of hypoglycemia by maintaining or increasing the concentration of
circulating glucose. Most of the common types of carbohydrates, such as glucose, sucrose,
and glucose polymers, are effective in maintaining blood glucose concentration, due to their
high glycemic index10.
• Prevents liver but not muscle glycogen depletion11,12. In addition, it can contribute to the
restoration of endogenous glycogen stores after exercise13.
• Stimulates the absorption of water and sodium in the small intestine.
Thus, the most important effect of carbohydrate intake is the improvement of physical
performance during prolonged exercise, since the mechanisms responsible for improving
endurance capacity have been related to the prevention of hypoglycemia, maintenance of a
high rate of carbohydrate oxidation, and, in some studies, sparing of glycogen14.
There has been much debate about the value of adding electrolytes to fluids ingested during
exercise. Normally, electrolyte replacement during exercise is not a priority and it is
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considered that, if a balanced diet is followed, its concentrations may be restored in the
post-exercise period.
However, the addition of sodium to beverages consumed during physical exercise promotes
rehydration as it:
• Stimulates the absorption of glucose and water in the small intestine. This is crucial when a
quick replacement is needed, such as during exercise.
• Stimulates the voluntary intake of fluids: it reduces the capacity of the drink to quench thirst
and improves its palatability. Sodium, being the main electrolyte in the extracellular fluid, is
closely involved in the homeostatic control of body water and, therefore, in many of the
sensory signals and mechanisms that control water intake15.
• Favors fluid retention: by raising plasma osmolality, urine production is reduced, allowing the
body to retain more of the water ingested, which allows the restoration of the volume of
extracellular fluid after exercise15.
• Prevents hyponatremia, a dangerous condition given in conditions of hyperhydration, during
which the serum concentration of sodium is abnormally low due to a dilution effect16.
Although only sodium plays an active role in the absorption of water and carbohydrates, it has been
speculated that the inclusion of potassium would improve intracellular water replenishment after
exercise and thus promote rehydration, but there is little evidence to support its inclusion17.
Potassium, which is the main osmotically active cation in the intracellular space, does not seem to
play a role like sodium in maintaining water balance15.
Although there is some loss of potassium in sweat, an increase in its plasma concentration is the
normal response to exercise, due to the release of potassium from working muscles and liver, as well
as from red blood cells and other tissues subjected to damage on the membrane7. Intense exercise
may cause hyperkalemia (potassium plasma concentration above 5.5 mM), followed by abrupt
hypokalemia (potassium plasma concentration below 3.5 mM) on exercise cessation, which can pose
a threat to stability of the myocardium and may contribute to sudden cardiac death18. Given this
situation, additional potassium increase through fluid intake during exercise may be
counterproductive.
In the case of magnesium, a slight decrease in its plasma concentration is generally observed during
exercise, which appears to be the result of a redistribution of storage sites7. Exercise cramps are
commonly associated with decreased plasma magnesium concentration; however, magnesium
supplementation for preventing these cramps has not shown any efficacy19.
Although alterations of the distribution of electrolytes, such as potassium and magnesium, within
the tissues have implications for the maintenance of their function, replacement is generally not a
problem since the movements between compartments are reversed in the post-exercise period7.
Ingestion and absorption of drinks
Gastric emptying
In situations where a rapid supply of exogenous nutrients or water is required, it is essential that
any beverage ingested is rapidly emptied from the stomach and rapidly and completely absorbed in
the small intestine. As these are critical elements for the effectiveness of any sports drinks, they are
formulated in such a way as to optimize these processes.
Gastric emptying is the transfer of stomach contents into the small intestine. The speed at which it
occurs is considered the main limiting factor for the assimilation of ingested fluids. The gastric
emptying rate of liquids is faster than that of solids. Therefore, nutrients and water supplied as
beverages are more rapidly absorbed and assimilated than are ingested as solid food15.
The main determinant of the rate of gastric emptying of a drink are the volume and the composition.
If the liquid is low in nutrients (for example, water), there is an exponential relationship between the
Isotonic sports drinks: formulation and physiological effects of their consumption
Ruiz, García
76 Facultad de Ciencias de la Salud. Universidad Técnica de Manabí. Portoviejo, Ecuador
volume and the rate of emptying: the higher the volume, the higher the rate. In contrast, if the fluid is
rich in nutrients, the rate of gastric emptying will be considerably slower and not exponential. In this
case, the energy density of the beverage is the main inhibitory regulator of gastric emptying;
increasing the energy density proportionally decreases the rate of gastric emptying. Carbohydrates
are the main source of energy in sports drinks, but other nutrients such as protein, fat, and alcohol
delay emptying to the same extent15. Any carbohydrate content in the drink will slow emptying, an
effect that becomes evident from a concentration of approximately 40 g/L3. Although increasing the
carbohydrate content of the drink decreases the rate of gastric emptying, it usually results in a higher
rate of carbohydrate delivery to the duodenum. To some extent, increasing beverage osmolality also
slows gastric emptying, but this effect is very slight at typical sports drink concentrations.
Intestinal absorption
The process of absorption of the components of a drink occurs in the small intestine. Water
absorption is a passive process that occurs by osmotic action only, but it is closely related to active
solute transport. If sodium and sugars are also present in the ingested fluid, then active transport
mechanisms operate, which promote water absorption. This, in turn, promotes the absorption of
solutes through a phenomenon known as solvent drag15.
Sodium is absorbed into the cell by various mechanisms, but the main one is by co-transport with
glucose and amino acids. This means that the efficient absorption of sodium depends on the
absorption of these organic solutes. Water diffuses in response to the osmotic gradient created by
sodium15.
In the small intestine, glucose is directly absorbed by an active, Na+-dependent transport system,
while a series of hydrolytic enzymes rapidly digest disaccharides and polysaccharides to their
monomeric forms, which are then efficiently transported across the mucosa by transportation systems.
The rate of glucose absorption through the active transport system reaches its maximum at a
glucose concentration of 200 mmol/L, but tends to continue to increase through mechanisms such as
diffusion down the concentration gradient and solvent drag, until 555 mmol/L. That is, the maximum
rate of glucose absorption occurs in solutions with glucose concentrations of 3.6 to 10.0%15.
In contrast, fructose is absorbed by a facilitated transport mechanism, its absorption rate is
approximately 2/3 that of glucose. Moreover, since it tends to accumulate in the intestine, the intake
of large amounts of fructose should be avoided, as it can cause gastrointestinal discomfort and
diarrhea. There are no other nutrients, apart from carbohydrates and sodium, which are necessary to
stimulate water absorption15.
Osmolality plays a key role in the flow of water through the upper part of the small intestine. Water
absorption is isotonic. That is, water is not absorbed until what has been ingested has been diluted to
a level equal to the osmolality of the blood. The osmolality of blood serum varies slightly within
individuals and from person to person, but it is usually considered to be 287 mOsm/kg. Any solution
with an osmotic pressure equivalent to that of serum is considered isotonic, if its osmolality is lower,
hypotonic, and if it is higher, hypertonic3.
The net flux of water is largely determined by the osmotic gradient between the luminal contents
and the intracellular fluid of the cells lining the intestine. The effect is concentration-dependent; the
maximum rate of water absorption occurs when solute concentrations result in a slightly hypotonic
solution (200 to 250 mOsm/kg)3. The time required to achieve isotonicity reduces the rate of net water
absorption.
Therefore, when the content of the lumen is significantly hypertonic, water is secreted from the
plasma into the intestine by osmotic action; this is a dehydrating effect that results in lower rates of
water absorption3. Hypertonic solutions are eventually absorbed. This delay, along with the initial net
movement of water from the circulation to dilute luminal contents, makes hypertonic solutions
ineffective in promoting fast rehydration.
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Isotonic sports drinks. Formulation
Isotonic sports drinks are those that contain carbohydrates and electrolytes at the same osmotic
pressure as blood. There is no international standard definition that includes formulation requirements
for carbohydrate and electrolyte solutions; however, entities such as the European Food Safety
Authority (EFSA) and the Food Standards of Australia and New Zealand have made
recommendations in this regard20,21.
Carbohydrates
Carbohydrates should be the main source of energy and it is recommended that they provide 80 to
350 kcal/L of beverage, which corresponds to a concentration range of 20 to 87 g/L. At least 75% of
the energy must be derived from metabolizable carbohydrates, characterized by a high glycemic index
(glucose, glucose polymers, and sucrose)20. Another recommendation establishes that they must
contain between 50 and 100 g/L of glucose, fructose, glucose syrup, maltodextrin, and/or sucrose,
with the amount of fructose being lower than 50 g/L21.
The amount of carbohydrates in the sports drink will be that which allows a balance between the
energy content and the inhibition of gastric emptying. A too low concentration will not optimize the
flavor of the drink and will not supply enough carbohydrates to enhance exercise performance. On
the other hand, excess carbohydrates delay gastric emptying and intestinal absorption, can cause
gastrointestinal disorders (>10% w/v) and a feeling of satiety, and may impair palatability15,22.
Sports drinks typically contain between 60 and 80 g of carbohydrates per liter. When deciding
which carbohydrate(s) will be used, the key factors are molar weight (MW) (and therefore its
contribution to osmolality), sweetening power, and electrolyte content3. Some types of commercially
available carbohydrates are3:
• Glucose: its low MW (180 g/mol) produces a greater impact on osmolality It has low
electrolyte content.
• Fructose: with a low MW (180 g/mol), it is not rapidly absorbed in the intestine and is not
readily available for muscle use since it is metabolized in the liver.
• Sucrose: MW of 342 g/mol, it has a lower contribution to osmolality per gram than
monosaccharides. It has a negligible quantity of electrolytes. In acid solutions, it is inverted
into glucose and fructose, reducing its MW by half, and causing an increase in osmolality.
• Glucose syrup: it is a complex mixture of sugars produced by hydrolysis of starch. Available
in various degrees of dextrose equivalence (DE), from 42 to 95 DE. As DE increases, average
MW decreases and sweetness increases. It has a moderate electrolyte content.
• High fructose corn syrup: produced from the partial enzymatic conversion of glucose to
fructose. It has an approximate composition of 42% fructose, 52% glucose, and 6% higher
saccharides. Its MW is like that of glucose syrup with 95 DE. It is sweeter than glucose syrup
and it has minimal electrolyte content. The presence of fructose is not desirable, but low levels
of this syrup does not provide more fructose than partially inverted sucrose.
• Maltodextrins: produced by the partial hydrolysis of starch. They range of DE is from 15 to
30 and have a very high average MW (typically 1100 g/mol for 15 DE). They have a high
content of electrolytes and virtually no sweetness.
Several papers have been published regarding the merits of different carbohydrates, but aside from
the above considerations, any commercially available sugars could be used. The exception is fructose,
which, being absorbed more slowly and metabolized in the liver, is not readily available for oxidation
and can cause gastrointestinal discomfort3.
Mixing different carbohydrates can be beneficial: 1) by providing solutes that are absorbed by
different mechanisms, it can maximize the rate of absorption of sugars and water in the small
Isotonic sports drinks: formulation and physiological effects of their consumption
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78 Facultad de Ciencias de la Salud. Universidad Técnica de Manabí. Portoviejo, Ecuador
intestine; 2) it has implications on the taste, which can positively influence the amount of drink
consumed; 3) allows better management of the osmolality of the product during its formulation. That
is why in most commercial sports drink various forms of carbohydrates are combined11.
Electrolytes
Ideally, hydrating drinks should have a sodium concentration like that of sweat, but since the
sodium content of sweat varies widely between people, a single formulation is not possible. The
sodium concentration of most sports drinks ranges from 10 to 30 mmol/L, while most fruit juices and
soft drinks contain virtually no sodium13.
The Australia and New Zealand food standards establishes a minimum sodium concentration of 10
mmol/L and the EFSA recommends 20-50 mmol/L (460-1150 mg/L)20,21. It can be added in the form
of salts, such as sodium chloride or sodium citrate3,21. Sodium intake in very low amounts discourages
the need to drink, stimulates urine production, and therefore delays the hydration process22. Very high
concentrations of sodium can lead to the perception of the drink as too salty, an important defect that
can reduce voluntary consumption. Due to its importance, this problem must be evaluated during the
formulation of any new hydration drink17.
Although only sodium plays an active role in the absorption of water and carbohydrates, sports
drinks are often also fortified with potassium, magnesium, calcium, and chloride, which are added in
concentrations like those in sweat3. It is possible to use salts such as3,21: potassium (chloride, citrate,
phosphate); calcium (chloride, lactate), and magnesium (chloride, sulfate). However, the presence of
these do not have a discernible impact on the absorption of water and carbohydrates and may produce
an increase in the osmolality of the solution15.
Other components
Sports drinks were originally developed as relatively simple solutions of carbohydrates and
electrolytes in known amounts. However, today it is common to find ingredients such as high-
intensity sweeteners, aromas, flavorings, and colorants, added to improve palatability, in commercial
sports drinks.
Vitamins are also included in many formulations. Some concern has been fueled by the idea that
fluid loss during sweating increases the loss of water-soluble vitamins, or that the high metabolic
demands of training athletes increase vitamin requirements. However, the available research indicates
that sweat is not a significant route of loss of these vitamins. Although thiamin is linked to
carbohydrate metabolism, it has not been shown to improve this by supplementation with any of the
B2 complex vitamins23.
Antioxidant vitamins A, C, and E can help in scavenging free radicals that form within the muscle,
which occurs at a higher rate during strenuous physical activity. Therefore, they could be valuable
for post-exercise recovery drinks3.
The addition of other ingredients such as starch, amino acids, proteins, lipids, glycerol, alcohol,
caffeine, organic acids, and herbs have also been investigated. They have been studied for their ability
to induce increased fluid absorption or increased performance, but so far without convincing success.
The addition of amino acids to a sports drink does not offer any benefits for sports performance.
Amino acids in solution are not stable during storage for long periods and, even under the best
circumstances, their presence may negatively affect the overall palatability and acceptance of
beverages. The addition of caffeine to beverages limits the effectiveness of hydration due to its
diuretic effect. Beer has been considered as a beverage with the potential to stimulate hydration, both
due to its composition and its high acceptance among consumers but, as with caffeine, alcohol has
diuretic properties.
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Carbonation promotes gastric emptying since carbon dioxide occupies an additional volume in the
stomach. However, carbonated drink consumed during exercise has a strong negative impact on its
acceptability, due to the burning sensation in the throat caused by the presence of high volumes of
CO222.
Lastly, sports drinks are not good vehicles for delivering nutrients because the doses that can be
included without adversely affecting taste and physiological efficacy are quite small15.
Osmolality
The osmotic pressure of a solution is a colligative property, that is, it is proportional to the number
of solute particles present in the solution. Most sports drinks are formulated to be isotonic and thus
optimize absorption in the intestine, which favors the rapid assimilation of its constituents24. Although
water absorption is optimal with slightly hypotonic solutions, as stated above, higher osmolality is
unavoidable when adequate amounts of carbohydrate are incorporated into the sports drink3.
An osmolality range between 200 and 330 mOsm/kg of water is recommended. Beverages with an
osmolality of 300 mOsm ± 10% of the range (270-330 mOsm/kg of water) can be designated as
isotonic20. However, the composition of the beverages and the nature of the solutes are just as
important as the osmolality itself.
Hyperosmolality has a dehydrating effect and delays absorption. However, small variations are not
clinically significant. Therefore, slightly hypertonic solutions with an osmolality of 340 to 400
mOsm/kg can still be effectively used as sports drinks25.
Today's sports drinks are complex solutions of nonionic and ionic substances; the latter will
dissociate to different degrees depending on their nature and the rest of the solutes present. The
osmolality of formulated beverages can be estimated by calculations from tables available, for
example, in the Handbook of Chemistry and Physics, The Merk Index, and The British Pharmacopeia.
The osmolality of ingredients for which no data is available can be calculated from the osmolality of
substances of similar MW and ionic character3.
Theoretical estimates of osmolality should be checked by direct measurement with an osmometer.
This equipment determines osmolality through the measurement of some colligative properties, such
as melting point depression. A molar solution of a non-ionic substance will produce a freezing point
depression of about 1.86 °C, but for ionic substances, the decrease will be 1.86 multiplied by the
number of ionic components generated per molecule3.
Final formulation
Once the carbohydrate system and the salt content, which is close to the desired level, have been
chosen, a first drink prototype can be proposed. The sweetness will then be adjusted by the addition
of high-intensity sweeteners, a level of acidity will be selected, and flavor, color, and preservatives
will be added at appropriate levels3.
Afterwards, the osmolality must be set. A reduction can be achieved by substituting low MW
sugars for a maltodextrin, or by reducing the total carbohydrate content. An increase can be achieved
by making the opposite changes. Typically, 70% of the osmolality of the beverage is due to the
carbohydrate content, 10% to salts, 15% to juice/flavor/acids/high-intensity sweeteners, and 5% to
carbonation (if any)3.
Palatability
Physical activity alters the hedonic characteristics of beverages in a way that a beverage that may
be preferable in sedentary conditions, may be rejected during exercise. For this reason, a properly
formulated isotonic carbohydrate-electrolyte sports drink has organoleptic characteristics that are
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Ruiz, García
80 Facultad de Ciencias de la Salud. Universidad Técnica de Manabí. Portoviejo, Ecuador
most valued when people are hot, sweaty, and thirsty. Therefore, it is essential to conduct sensory
field surveys with athletes during and after physical activity. Aspects that require attention are
sweetness, acidity, and flavor type and intensity26.
Taste is a very important element in promoting voluntary fluid intake. Some flavorings added to
hydration drinks mask the taste of salt. In addition to flavor, beverage temperature can affect a variety
of sensory and physiological functions, directly influencing the volume consumed. Temperature of
15 °C is considered as ideal for fluid intake26.
The palatability of sports drinks is measured in a variety of ways, either using scaling techniques
(e.g., a 9-point verbal hedonic scale) or inferred from differences in voluntary fluid intake.
Achieving the optimal balance between sports drink efficacy and palatability is a significant
challenge for manufacturers. From a food science perspective, sports drinks are relatively simple
beverage systems, and that fact makes it difficult to manipulate the types and amounts of solutes
without having an immediate and noticeable effect on palatability.
Physiological effects of the consumption of isotonic sports drinks
Beneficial effects
Research agrees that isotonic sports drinks, consumed before, during, and after prolonged and
intense exercise or other strenuous physical activity, are more effective than water in preventing
dehydration, helping to maintain exercise performance, delaying the onset of fatigue, and accelerating
recovery20,27,28. For the restoration of carbohydrate and electrolyte levels, it is recommended to drink
120 to 180 mL of sports drinks every 15 minutes during vigorous exercise29.
Some sports are especially demanding due to their duration and intensity, such as soccer, long-
distance running, cycling, and tennis, among others. For example, when sports drinks were consumed
before, during, and after playing tennis, the decrease in exertional capacity was minimal and
performance was improved compared to situations in which the only liquid consumed was water30.
The behavior of the plasma concentration of sodium during physical exercise is not distinguished
by a specific response. Its change can be variable, meaning that hyponatremia or hypernatremia could
occur or that there would be no alteration. However, it seems that, during too much exercise, an
isotonic drink containing sodium can reduce the possibility of hyponatremia31.
Adverse effects
Isotonic drinks may have adverse effects if they are consumed in excess. They can cause a
deterioration of dental enamel due to the erosive potential imparted by some compounds that appear
in certain brands. Dental deterioration appears to be more related to the frequency of consumption
than to the quantity consumed. Athletes belong to the highest risk group since with physical activity,
fluids are lost and the volume of saliva is reduced, which is an important buffer for acids in the mouth.
However, it is believed that the calcium content of isotonic drinks could protect against this erosive
effect, which could justify their incorporation in the formulation32.
Isotonic sports drinks from natural products
Sports drinks available on the market often contain flavorings, sweeteners, and other synthetic
compounds. Currently, and because of consumer demand for more natural products, the sports
nutrition industry is looking for alternatives to traditional sports drinks.
The carbohydrate content of a fruit juice diluted at 50% is like that of a commercial isotonic sports
drink, so it can be used for fluid replacement during exercise. Most juices lack the necessary
electrolytes, so they can be fortified with sodium chloride. Fruit juices are easily accessible,
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affordable drinks that are widely accepted by consumers. A simple substitute for sports drinks like
Gatorade and Powerade® could be diluted with 50% of apple juice and mixed with sodium chloride.
Gatorade® contains 6% carbohydrates, while an apple juice diluted at 50% contains 5.9%
carbohydrates, which is a very similar amount33.
A diluted juice drink that is as effective as a commercial sports drink in rehydration and
performance enhancement would not only have economic advantages, but it could provide additional
beneficial nutrients and phytochemicals not found in commercial sports drinks33.
It is possible to prepare a hydrating drink with natural ingredients, which can be cheaper and
healthier and can produce beneficial effects on physical performance, in a similar way to commercial
sports drinks. An example would be the mixture of 5 g of baking soda, 5 g of kitchen salt, 2
tablespoons of sugar, the juice of 2 citrus fruits, and 1 L of water34. The drawback is that its isotonicity
cannot be guaranteed.
Several isotonic sports drinks have been developed from fruits, cereals, and other natural
ingredients. An example of this is the isotonic sports drink designed by López et al.35 from an apple
concentrate with the addition of sodium, potassium, magnesium, and calcium salts, in addition to
vitamins B1, B2, B6, B12, C, E, folic acid, niacin, pantothenic acid and biotin contained in the
concentrate. An isotonic energy drink with almond milk can be obtained by blanching and crushing
almonds, adding fruit juices or infusions, pasteurizing the mixture, correcting the loss of nutrients,
and a final stage to adjust pH and osmolality, which is 275 mOsm/kg approximately36.
Penggalih et al.37 developed an isotonic sports drink from banana flour, with an osmolality of 269
mOsm/kg. Later, Afriani et al.38 studied the effect of this drink on maintaining hydration, through the
measurement of the level of electrolytes (chloride, sodium, and potassium) in plasma and urine. The
product was able to maintain the body's normal electrolyte levels by reducing the amount of those
electrolytes eliminated through urine.
An isotonic sports drink was also developed from pineapple (Ananas comosus L.) juice using a D-
optimal blend design. The beverages with the highest percentages of sucrose and pineapple juice
turned out to be the ones with the highest osmolality and sensory acceptance. A drink containing
pineapple juice (34.0%; 628 mOsm/kg), distilled water (62.8%), sucrose (3.1%), and NaCl (0.1%; 20
mmol/L) was obtained, which had 7.7% of total sugars, an osmolality of 328 mOsm/kg and an
adequate sensory acceptance39.
Some researchers have focused on substituting synthetic food additives usually found in
commercial sports drinks for natural substances. For example, Bovi et al.40 were able to successfully
produce an isotonic sports drink with a nanoemulsion of buriti oil as coloring agent, in substitution
of artificial dyes. Similarly, Porfírio et al.41 used a hydroethanolic extract of peel and pulp of
Myrciaria jaboticaba to add dark red color to an isotonic beverage.
More recently, spray drying was applied to a mixture of honey, plant infusions, fruit juices, and
salt, to prepare powdered isotonic sports drinks with enhanced antioxidant properties and a variety of
colors and flavors, depending on the ingredients used in each formulation42.
Conclusions
The benefits of consuming isotonic sports drinks are proven in athletes and individuals who
perform strenuous, long-lasting physical exercises or in very hot environments; however, its
consumption should not be encouraged in people who only engage in moderate physical activity,
especially children and adolescents. In addition, its consumption must be combined with a balanced
diet that provides essential macro and micronutrients. Further research is required to personalize, by
optimizing, the amount of each of the ingredients in isotonic drinks, based on individual preferences
and exercise characteristics, and to develop alternatives to commercially available sports drinks using
natural ingredients, following market trends.
Isotonic sports drinks: formulation and physiological effects of their consumption
Ruiz, García
82 Facultad de Ciencias de la Salud. Universidad Técnica de Manabí. Portoviejo, Ecuador
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