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Qu’est-ce qu’une boisson isotonique ?

What is an isotonic drink?

Perhaps you have already heard of so-called effort, sports or energy drinks, all these names refer to the “ isotonic ” drink.

A drink is isotonic when its osmolarity is close to that of blood plasma.

Osmolarity is expressed in mOsm/L, to read milliosmoles per liter of solute, corresponds to the number of osmotically active particles ( electrolytes ), which exert pressure on a membrane, in a solution. There is also osmolality, which is the same thing expressed in mOsm/kg, only the units change.

Plasma osmolarity, which is approximately 300 mOsm/L, is used as a reference for beverage osmolarity. Thus, there are three types of drinks:

  • The isotonic drink whose osmolarity will be between 270 and 330 mOsm/L, approaching that of plasma.
  • The hypotonic drink , which has a lower osmolarity than plasma, between 150-200 mosm/L
  • The hypertonic drink, on the other hand, has a higher osmolarity than plasma.


What do hypotonic, isotonic and hypertonic drinks contain?

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

For a drink to have the same osmolarity as plasma, it must have enough molecules exerting an osmotic pressure on the membranes equivalent to that of plasma. Plasma osmolarity is calculated by taking into account sodium, potassium, blood sugar and uremia, that is to say the rate of sodium, potassium, glucose and urea because these are the molecules osmotically majority active 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 body hydration. It allows you to reconstitute an isotonic or hypotonic drink easily and studied not only to hydrate effectively but also to facilitate recovery and fight against oxidative stress of cells. Thanks to their sodium, glucose, potassium and chloride composition, you just need to dilute 2 lozenges in 500mL of water for an isotonic drink or 1 lozenge 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 quantities of sugar and mineral salts than plasma such as sodas. These drinks are to 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 very well compensate for the loss of sugars but can aggravate the loss of water.

To understand it, you have to imagine a membrane with, on the one hand, a hypertonic liquid and on the other hand the plasma. The hypertonic medium is more concentrated than plasma, this will result in a movement of electrolytes to restore a state of equilibrium. Here, the electrolytes will flow from the more concentrated medium (hypertonic fluid) 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 causing a loss of water and occasional 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!

Why drink an isotonic drink?

The interest of isotonic drinks during the effort is multiple. During an intensive sports session such as a long run (marathon, trail, etc.) your body loses water and electrolytes.

An isotonic drink allows you to compensate for these losses since you provide your body with water, electrolytes and carbohydrates all at once. But the benefit of an isotonic drink goes beyond simple compensation for losses since the alloy of electrolytes, carbohydrates and water with an osmolarity similar to blood plasma maximizes their absorption by the body and therefore your level. of hydration!

Indeed, osmolarity has an impact on 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 either side of this membrane is equivalent, the electrolyte concentrations are the same, the exchanges around this membrane will therefore be balanced. The isotonic drink restores electrolytes and water losses continuously to avoid dehydration precisely, moreover, if dehydration occurs during an effort, the plasma will become hypertonic rather than hypotonic because the water losses will be greater than the electrolyte losses .

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

The cotransport mechanism of isotonic drinks

To fully understand the mechanism of isotonic drinks, it is necessary to understand the mechanism of cotransport of liquids. There are several modes of movement of molecules classified into two main categories:

  • A so-called passive diffusion, i.e. the molecule passes alone through the membrane, according to a concentration gradient
  • The second mode of absorption is active, this means that the molecule requires a transporter and energy to pass the membrane, of which the cotransport mechanism is a part.

Among the components of the isotonic drink, water will pass through the intestinal membrane to the blood plasma passively, by diffusion. Electrolytes can pass the intestinal membrane passively, actively, or both. This is particularly the case for sodium which, initially, needs glucose to be absorbed by the intestinal cell: it is a cotransport mechanism.

Sodium and glucose pass through a transporter that needs the presence of both molecules to transfer them from the intestinal lumen into the cell interior. Then the sodium leaves the other side of my cell by active transport and passively diffuses into the plasma. Sodium helps maintain osmolarity and therefore participates in facilitating the absorption of water and electrolytes.

[ glucose sodium cotransport ]

When to drink isotonic drinks?

Due to its properties, the isotonic drink is the ideal ally for hydration during exercise, allowing you to stay hydrated throughout your sports session, compensating for your water and electrolyte losses quickly and optimally thanks to the alliance of glucose with electrolytes, also ensuring a necessary nutritional contribution to your body.
You can nevertheless choose a hypotonic drink if you do long-term physical activity and in high heat when the priority is to compensate for water losses rather than sugar losses.

Hydratis allows you to concoct your effort drinks simply wherever you are, thanks to airtight tubes that can be transported everywhere. Rediscover the pleasure of drinking an isotonic or hypotonic flavored drink to keep you going and improve your performance by staying well hydrated.

Find more details during our interview on Europe 1 as well as our products on the Hydratis Shop .

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