What is an isotonic drink?

Perhaps you have already heard of so-called sports drinks, energy drinks , or even energy 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), which 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:

• Isotonic drink, whose osmolarity is between 270 and 330 mOsm/L, approaching that of plasma.

• Hypotonic drink, which has an osmolarity lower than plasma, between 100 and 270 mOsm/L.

• 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 so as to bring its osmolarity closer 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 support exercise. Different forms of sugars can be present, such as glucose, fructose, or sucrose.

Why drink an isotonic drink?

Isotonic drinks during exercise have several uses, particularly during an intensive sports session such as a long race ( marathon , trail, running, etc.). In these 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 by providing your body with water, minerals, and carbohydrates in a single intake. But the benefits of an isotonic drink go beyond simply compensating for losses, since the combination of electrolytes, carbohydrates, and water, with an osmolarity similar to blood plasma, will maximize their absorption by the body and therefore your hydration level!

Indeed, osmolarity has an impact on the movement of water and osmotically active molecules on either side of a membrane. Let's 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 the exchanges around this membrane will be balanced. The isotonic drink provides the energy necessary during your physical efforts and compensates for water losses continuously to avoid dehydration . It's ideal for exercise!

In your body, the liquid you drink ends up in your intestine where absorption and exchange with the plasma take place. If you drink a hypertonic liquid, the exchanges between the external environment (intestine) and the blood plasma will be unbalanced, the absorption of water will not be as efficient as with an isotonic drink where the two environments are balanced.
[ osmotic movement ]

When should you drink an isotonic drink?

Thanks to its specific properties, the isotonic drink is particularly suitable for physical exertion, in particular to provide energy while ensuring a minimum of hydration. It helps 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 cases of high heat or excessive sweating, a hypotonic drink can be used in addition to the isotonic drink, in order to maximize water intake and avoid dehydration, particularly when the issues are related to hydration.

What are the differences between hypotonic, isotonic and hypertonic drinks?

Hypotonic drinks are low in solutes, for example, drinks like tea or mineral water. They contain electrolytes (sodium, bicarbonates, potassium, etc.) in a lower proportion compared to blood plasma. This type of drink is particularly suitable for maintaining hydration for a long time . Indeed, thanks to its composition rich in water compared to plasma, the absorption of water will be favored over that of electrolytes: on the one hand because the water will go from the most dilute medium (hypotonic drink) to the plasma, and on the other hand because the electrolytes contained in the most concentrated medium (plasma) will go to the less concentrated medium, until the two environments are balanced.

For a beverage to have the same osmolarity as plasma, it must have enough molecules exerting osmotic pressure on the membranes, equivalent to that of plasma. To calculate plasma osmolarity, we take into account the natremia, the kalemia, the glycemia and the uremia, that is to say the level of sodium, potassium, glucose and urea because these are the majority osmotically active molecules in plasma, although electrolytes such as chloride or bicarbonates also participate.

The isotonic drink therefore preferably contains sodium, potassium and glucose, diluted in a sufficient quantity of water. Hydratis is a solution specifically dedicated to hydrating the body . It will allow you to easily create an isotonic or hypotonic drink and has been designed not only to hydrate effectively but also to facilitate recovery and combat oxidative stress in cells . Thanks to their practical format and their composition of sodium, glucose, potassium and chloride, you just need to dilute 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 since they contain higher amounts of sugar and mineral salts than plasma, like sodas in particular. These drinks should be consumed when you are looking to provide your body with nutrients and energy as a priority and when you are not at risk of dehydration. Indeed, hypertonic drinks will compensate for sugar losses very well but can aggravate water losses!

To understand this, we need to imagine a membrane with, on one side, a hypertonic liquid and on the other side, plasma. The hypertonic medium is more concentrated than plasma, resulting in a movement of electrolytes to restore a state of equilibrium. Here, the electrolytes will move from the more concentrated medium (hypertonic liquid) to the plasma. Associated with this movement, there will also be a leakage of water from the less concentrated medium (plasma) to the more concentrated medium (hypertonic liquid) until equilibrium is reached, thus leading to a loss of water and occasionally digestive discomfort. This is why you should not consume a hypertonic drink if you want to hydrate yourself since the effect will be the opposite!

What are the differences between isotonic and electrolyte drinks?

As previously stated, isotonic drinks vs. electrolytes are primarily water with electrolytes, but aim to maintain a very precise proportion to promote assimilation by the body. However, for very specific needs, such as a deficiency of a particular electrolyte, more direct consumption of said electrolyte may then be the optimal solution.

Isotonic drinks are beverages designed to promote the absorption of water and electrolytes to prevent dehydration and optimize athletic performance and effort. They are therefore an asset in the sports world to maximize energy, although they are beneficial to any individual.

Hydratis lets you easily concoct your sports drinks wherever you are, thanks to its airtight tubes that can be transported anywhere. Rediscover the pleasure of drinking a flavored isotonic or hypotonic drink to stay energized and improve your performance while 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 .