Perhaps you have already heard of drinks called sports drinks, energy drinks , or sports drinks . All these names refer to the "isotonic" drink.
A drink is isotonic when its osmolarity is close to that of blood plasma , promoting its absorption .
Osmolarity 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 measurement, expressed in mOsm/kg.
The osmolarity of blood plasma, which is approximately 300 mOsm/L, is used as a reference. Thus, three types of drinks are distinguished:
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The isotonic drink, whose osmolarity is between 270 and 330 mOsm/L, is close to that of plasma.
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The hypotonic drink, which has an osmolarity lower than plasma, between 100 and 270 mOsm/L.
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The hypertonic drink has a higher osmolarity than 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 approximate its osmolarity 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 can also be found depending on the different solutions.
Carbohydrates , on the other hand, provide a quick source of energy to sustain exertion. Different forms of sugars can be present, such as glucose, fructose, or sucrose.
Why drink an isotonic beverage?
Isotonic drinks have several uses during exercise , particularly during intense workouts such as long-distance races ( marathons , trail runs, road races , etc.). In these situations, your body loses water and electrolytes to regulate your body temperature and burns calories to generate energy.
An isotonic drink helps replenish these losses by providing your body with water, minerals, and carbohydrates in a single serving. But the benefits of an isotonic drink go beyond simply replacing lost fluids, as the combination of electrolytes, carbohydrates, and water, with an osmolarity similar to blood plasma, maximizes their absorption by the body, thus boosting your hydration level!
Indeed, osmolarity impacts the movement of water and osmotically active molecules across a membrane. Imagine a membrane with plasma on one side and an isotonic fluid on the other. The osmotic pressure exerted on both sides of this membrane is equivalent, the electrolyte concentrations are therefore the same, and thus the exchanges around this membrane will be balanced. Isotonic drinks provide the necessary energy during physical exertion and continuously replenish lost fluids to prevent dehydration . They are ideal for exercise!
In your body, the liquid you drink ends up in your intestine where absorption and exchange with the blood plasma take place. If you drink a hypertonic liquid, the exchanges between the external environment (intestine) and the blood plasma will be unbalanced, and water absorption will not be as efficient as with an isotonic drink where the two environments are in balance.
[ osmotic movement ]
When should you drink an isotonic beverage?
Thanks to its specific properties, isotonic drinks are particularly well-suited for physical exertion, notably for providing energy while ensuring adequate hydration. They help maintain performance by replenishing carbohydrates and electrolytes, 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 the isotonic drink, in order to maximize fluid intake and avoid dehydration, especially when hydration is a key factor.
What are the differences between hypotonic, isotonic, and hypertonic drinks?
Hypotonic drinks are low in solutes; examples include tea and mineral water. They contain electrolytes (sodium, bicarbonates, potassium, etc.) in a lower proportion compared to blood plasma. This type of drink is particularly well-suited for maintaining hydration over extended periods . Indeed, thanks to its high water content relative to plasma, water absorption is prioritized over electrolyte absorption: firstly, because water will move from the more dilute environment (hypotonic drink) to the plasma, and secondly, because the electrolytes contained in the more concentrated environment (plasma) will move to the less concentrated environment until equilibrium is reached between the two.
For a beverage to have the same osmolarity as plasma, it must contain a sufficient number of molecules that exert an osmotic pressure on its membranes equivalent to that of plasma. To calculate plasma osmolarity, serum sodium, potassium, glucose, and urea levels are taken into account, as these are the predominant osmotically active molecules in plasma, although electrolytes such as chloride and bicarbonate also contribute.
Isotonic drinks therefore primarily contain sodium, potassium, and glucose, diluted in a sufficient amount of water. Hydratis is a solution specifically designed for It hydrates the body. It allows you to easily prepare an isotonic or hypotonic drink and has been studied not only for effective hydration but also to facilitate recovery and combat oxidative stress in cells . Thanks to their convenient format and composition of sodium, glucose, potassium, and chloride, you simply need to dissolve 2 tablets in 500ml of water to obtain an isotonic drink or 1 tablet in 250ml for a hypotonic drink.
[ plasma osmolarity ]
Hypertonic drinks, on the other hand, are particularly rich in electrolytes and sugars, as they contain higher amounts of sugar and minerals than plasma, like sodas for example. These drinks should be consumed when your primary goal is to provide your body with nutrients and energy, and when you are not at risk of dehydration. Indeed, while hypertonic drinks will effectively compensate for sugar loss, they can exacerbate water loss!
To understand this, imagine a membrane with, on one side, a hypertonic fluid and on the other, plasma. The hypertonic fluid is more concentrated than the plasma, resulting in a movement of electrolytes to restore equilibrium. Here, the electrolytes will move from the more concentrated fluid (hypertonic fluid) to the plasma. Associated with this movement, there will also be a loss of water from the less concentrated fluid (plasma) to the more concentrated fluid (hypertonic fluid) until equilibrium is reached, leading to water loss and occasionally digestive discomfort. This is why you shouldn't 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 drinks versus electrolyte drinks are primarily water with added electrolytes, but with a very precise ratio designed to promote absorption by the body. However, for very specific needs, such as a deficiency of a particular electrolyte, consuming that electrolyte directly may be the optimal solution.
Isotonic drinks are beverages designed to promote the absorption of water and electrolytes in order to prevent dehydration and optimize athletic performance and exertion. They are therefore a valuable asset in the sports world for maximizing energy, although they are beneficial to everyone.
Hydratis lets you easily prepare your sports drinks wherever you are, thanks to its portable, airtight tubes. Rediscover the pleasure of drinking a flavored isotonic or hypotonic beverage to stay energized and 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 booth. Exercise and fluid replacement. Med Sci Sports Exercise 2007 Feb;39(2):377-90. doi:10.1249/mss.0b013e31802ca597 .
