What is Osmolality?

Osmolality is a measure of the concentration of solutes (for example, carbohydrates and salts) in a solution, often expressed in millimoles per Litre of solvent (mmol/L). It's a crucial concept in sports nutrition, especially when it comes to hydration and the formulation of sports drinks.

Your blood has a certain osmolality, and so do the fluids that you drink. A beverage that has a higher osmolality than your body's fluids will arrive in your small intestine, where cells draw water out of the bloodstream to decrease the osmolality of the fluid in your gut. During hard physical exercise, this can lead to dehydration - not an outcome that we want!

High osmolality drinks are hypertonic. An example of a hypertonic drink is apple juice, soft drinks or overly concentrated sports drinks. High osmolality (hypertonic) drinks can lead to gastrointestinal symptoms if you're not careful. 

Drinks with a lower osmolality (hypotonic) can help with rehydration. Beverages that contain some carbohydrate/sugar and about 1,000 mg of sodium per litre are considered hypotonic. Water from a hypotonic drink will get pulled into the blood stream as the sugar and salts get absorbed. If you think that guzzling down plain water is the most effective rate to rehydrate, you'd be wrong. Including some salts and/or carbohydrates will speed up the process. 

Consuming too much of a hypotonic fluid during exercise can lead to over hydration and water retention. Some signs include puffy fingers you're exercising. The biggest risk however, is increased fluid retention in your brain, which can have serious consequences. 

For athletes, understanding osmolality can help in choosing the right hydration strategy. Isotonic drinks, which have the same osmolality as body fluids, are often preferred during exercise as they provide a balance of hydration and energy without causing gastrointestinal distress.

In everyday terms, osmolality can be thought of as the "strength" or "concentration" of a solution. For example, a sports drink with a high sugar content would have a higher osmolality, while one with less sugar would have a lower osmolality. The right balance ensures that the drink provides energy without upsetting the stomach or causing other hydration-related issues.