Perhaps you've already heard of so-called endurance drinks, sports drinks, or even energy drinks. All these terms refer to "isotonic" beverages.
A drink is isotonic when its osmolality is close to that of blood plasma, favoring its absorption.
Osmolality is expressed in mOsm/L (milliosmoles per liter of solute) and corresponds to the number of osmotically active particles (mainly electrolytes) that exert osmotic pressure on a membrane. Osmolarity is a similar measure, expressed in mOsm/kg.
We use the osmolality of blood plasma, which is approximately 300 mOsm/L, as a reference. Thus, three types of drinks are distinguished:
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Isotonic drinks, whose osmolality is between 270 and 330 mOsm/L, similar to that of plasma.
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Hypotonic drinks, which have an osmolality lower than plasma, between 100 and 270 mOsm/L.
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Hypertonic drinks have an osmolality higher than that of plasma.
What do isotonic drinks contain?
Isotonic drinks contain sugars (carbohydrates), electrolytes, and, of course, water. The proportion of electrolytes to water is chosen to bring its osmolality close to the 300 mOsm/L of blood plasma.
The most important electrolytes are sodium and potassium, but magnesium, calcium, and other minerals or trace elements may also be found depending on the specific solution.
Carbohydrates, for their part, provide a rapid energy source to support exertion. Different forms of sugars may be present, such as glucose, fructose, or sucrose.
Why drink an isotonic drink?
Isotonic drinks during exercise have several uses, especially during intensive sports sessions like long-distance races (marathon, trail running, running...). In such cases, your body loses water and electrolytes to regulate your body temperature and burns calories to generate energy.
An isotonic drink allows you to compensate for these losses as you provide your body with water, minerals, and carbohydrates in a single intake. But the benefit of an isotonic drink goes beyond simple compensation for losses, as the combination of electrolytes, carbohydrates, and water with an osmolality similar to blood plasma will maximize their absorption by the body and thus your hydration level!
Indeed, osmolality impacts the movement of water and osmotically active molecules across a membrane. Imagine a membrane with plasma on one side and an isotonic liquid on the other. The osmotic pressure exerted on both sides of this membrane is equivalent, the electrolyte concentrations are then the same, so exchanges around this membrane will be balanced. The isotonic drink provides the necessary energy during your physical efforts and continuously compensates for water loss to prevent dehydration. It's ideal for exertion!
In your body, the liquid you drink ends up in your intestine where absorption and exchanges with plasma occur. If you drink a hypertonic liquid, the exchanges between the external environment (intestine) and blood plasma will be unbalanced; water absorption will not be as efficient as with an isotonic drink where both environments are balanced.
[osmotic movement]
When should you drink an isotonic drink?
Thanks to its specific properties, isotonic drinks are particularly suitable for physical exertion, especially to provide energy while ensuring minimum hydration. They help maintain performance by compensating for carbohydrate and electrolyte losses, thanks to the combination of glucose and mineral salts, thus promoting rapid absorption and effective recovery.
In case of high heat or excessive sweating, a hypotonic drink can be used in addition to an isotonic drink, to maximize fluid intake and prevent dehydration, especially when the stakes are related to hydration.
What are the differences between hypotonic, isotonic, and hypertonic drinks?
Hypotonic drinks are low in solutes; these include drinks like tea or mineral water. They contain electrolytes (sodium, bicarbonates, potassium...) in a smaller proportion compared to blood plasma. This type of drink is particularly suitable for maintaining hydration over a long period. Indeed, thanks to its water-rich composition compared to plasma, water absorption will be favored over that of electrolytes: partly because water will move from the most dilute environment (hypotonic drink) to the plasma, and partly because the electrolytes contained in the most concentrated environment (plasma) will move to the least concentrated environment until equilibrium between the two environments is reached.
For a drink to have the same osmolality as plasma, it must have enough molecules exerting osmotic pressure on the membranes, equivalent to that of plasma. To calculate plasma osmolality, we consider natremia, kalemia, glycemia, and uremia, i.e., the levels of sodium, potassium, glucose, and urea, as these are the major osmotically active molecules in plasma, although electrolytes such as chloride or bicarbonates also contribute.
Isotonic drinks therefore preferentially contain sodium, potassium, and glucose, diluted in a sufficient quantity of water. Hydratis is a solution specifically dedicated to body hydration. It allows you to easily prepare an isotonic or hypotonic drink and has been designed not only for effective hydration but also to facilitate recovery and fight against cellular oxidative stress. Thanks to their practical format and composition of sodium, glucose, potassium, and chloride, you just need to dilute 2 tablets in 500mL of water for an isotonic drink or 1 tablet in 250ml for a hypotonic drink.
[plasma osmolality]
Hypertonic drinks, on the other hand, are particularly rich in electrolytes and sugars as they contain higher amounts of sugar and mineral salts than plasma, such as sodas. These drinks should be consumed when you are primarily looking to provide nutrients and energy to your body and are not at risk of dehydration. Indeed, hypertonic drinks will very well compensate for sugar losses but can worsen water losses!
To understand this, imagine a membrane with a hypertonic liquid on one side and plasma on the other. The hypertonic environment is more concentrated than plasma, resulting in a movement of electrolytes to restore a state of equilibrium. Here, electrolytes will move from the more concentrated environment (hypertonic liquid) to the plasma. Associated with this movement, there will also be a leakage of water from the less concentrated environment (plasma) to the more concentrated environment (hypertonic liquid) until equilibrium is reached, thereby leading to water loss and occasionally digestive discomfort. This is why you should not consume a hypertonic drink if you want to hydrate yourself, as the effect will be the opposite!
What are the differences between isotonic and electrolyte drinks?
As previously established, isotonic vs electrolyte drinks are primarily water with electrolytes but aim to maintain a very precise proportion that promotes assimilation by the body. However, for very specific needs, such as a deficiency of a particular electrolyte, the more direct consumption of said electrolyte may then be the optimal solution.
Isotonic drinks are designed to promote the assimilation of water and electrolytes to prevent dehydration and optimize athletic performance and efforts. They are therefore an asset in the sports world for maximizing energy, even if they are beneficial to everyone.
Hydratis allows you to easily prepare your endurance drinks wherever you are, thanks to airtight tubes that can be carried anywhere. Rediscover the pleasure of drinking a flavored isotonic or hypotonic drink to stay energized and thus improve your performance by staying well hydrated!
Bibliography
Rowlands DS, Kopetschny BH, Badenhorst CE. The Hydrating Effects of Hypertonic, Isotonic and Hypotonic Sports Drinks and Waters on Central Hydration During Continuous Exercise: A Systematic Meta-Analysis and Perspective. Sports Med. 2022 Feb;52(2):349-375. doi: 10.1007/s40279-021-01558-y
American College of Sports Medicine; Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS. American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc. 2007 Feb;39(2):377-90. doi: 10.1249/mss.0b013e31802ca597.
