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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

* Mario A. García

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 fluids

. 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 injury

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 stores

. 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 activity

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

Universidad Técnica de Manabí, Facultad de Ciencias de la Salud, Doctor en Ciencias de los Alimentos, Departamento de Ciencias Biológicas, Portoviejo, Manabí,

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 health

. 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 exercise

. 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 discomfort

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 water

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 role

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

consumed

• 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 index

• Prevents liver but not muscle glycogen depletion

11,12

. In addition, it can contribute to the

restoration of endogenous glycogen stores after exercise

• 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 glycogen

 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 intake

• 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 exercise

• Prevents hyponatremia, a dangerous condition given in conditions of hyperhydration, during

which the serum concentration of sodium is abnormally low due to a dilution effect

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 inclusion

Potassium, which is the main osmotically active cation in the intracellular space, does not seem to

play a role like sodium in maintaining water balance

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 membrane

. 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 death

. 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 sites

. Exercise cramps are

commonly associated with decreased plasma magnesium concentration; however, magnesium

supplementation for preventing these cramps has not shown any efficacy

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 period

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 food

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 extent

. Any carbohydrate content in the drink will slow emptying, an

effect that becomes evident from a concentration of approximately 40 g/L

. 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 drag

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

sodium

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%

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 absorption

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, hypertonic

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)

. 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 absorption

. 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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Facultad de Ciencias de la Salud. Universidad Técnica de Manabí. Portoviejo, Ecuador 77

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 regard

20,21

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)

. 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/L

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 palatability

15,22

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 content

. Some types of commercially

available carbohydrates are

• 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 discomfort

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 combined

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 sodium

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 citrate

3,21

. Sodium intake in very low amounts discourages

the need to drink, stimulates urine production, and therefore delays the hydration process

. 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 drink

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 sweat

. It is possible to use salts such as

3,21

: 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 solution

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

complex vitamins

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 drinks

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

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 small

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 constituents

. 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 drink

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

isotonic

. 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 drinks

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 character

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 molecule

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 levels

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)

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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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 intensity

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 intake

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

recovery

20,27,28

. 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 exercise

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 water

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 hyponatremia

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 formulation

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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Facultad de Ciencias de la Salud. Universidad Técnica de Manabí. Portoviejo, Ecuador 81

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 amount

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 drinks

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 water

. 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.

from an apple

concentrate with the addition of sodium, potassium, magnesium, and calcium salts, in addition to

vitamins B

, B

, 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 approximately

Penggalih et al.

developed an isotonic sports drink from banana flour, with an osmolality of 269

mOsm/kg. Later, Afriani et al.

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 acceptance

Some researchers have focused on substituting synthetic food additives usually found in

commercial sports drinks for natural substances. For example, Bovi et al.

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.

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 formulation

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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