Isotonic drinks are called those rehydrating drinks or sports drinks, that is, those with great rehydration capacity.

They include in their composition low doses of sodium, normally in the form of sodium chloride or sodium bicarbonate, sugar or glucose and, usually, potassium and other minerals.

These components help the absorption of water, which is vital for the proper functioning of the human body and the living being.

They should not be confused with energy drinks, nor with stimulating drinks, since they do not contain stimulating substances. They are drinks that replace the substances lost during physical activity.

They are isotonic or slightly hypotonic hydrating drinks, since an excessive concentration of solutes will hinder the absorption of water, even compared to water alone. For this not to happen, carbohydrates should not exceed 10% of the composition of the drink.

Other components that have been studied to improve water absorption are carbohydrates that do not increase osmolarity, that is, they do not make the drink hypertonic and hinder absorption, such as maltodextrin, a glucose polymer with less osmolarity; amino acids such as glycine, glutamine and alanine seem to have a function similar to that of glucose in the absorption of water; also some dipeptides or tripeptides that reduce osmotic pressure relative to amino acids.