# Do sports drinks hydrate better than water?

An isotonic sports drink counts as 525 ml per 500 ml bottle and carries 125 calories. What isotonic really means, and when the fuel is worth it.

## Numbers the app uses

| Field | Value |
| --- | --- |
| Default serving | 500 ml |
| Hydration factor | 1.05 |
| Counts toward the daily goal | 525 ml per serving |
| Calories | 25 kcal per 100 ml (125 kcal per serving) |

## "Isotonic" is a statement about your stomach

The word describes concentration, not benefit. An isotonic drink is mixed so
its osmolality is close to that of blood, near 290 milliosmoles per kilogram.
That lets it leave the stomach and cross the gut wall quickly. Make it more
concentrated and it sits there, drawing water into your intestine. That is what
a warm flat cola does to a runner at kilometre 30. The formula exists so that a
runner can swallow fuel at speed.

The carbohydrate load follows from the same target: about 6 g per 100 ml. That
is where the app's 25 calories per 100 ml comes from. A 500 ml bottle is 125
calories and roughly 30 g of carbohydrate. That is genuinely useful in the
second hour of hard exercise, and a soft drink on a desk.

## Level with water, well behind a rehydration solution

The Beverage Hydration Index trial included a commercial sports drink among its
thirteen beverages and measured urine output over four hours. It came out
alongside water. The two drinks that clearly held fluid better were milk and
oral rehydration solution, and the reason is salt. A rehydration solution
carries several times the sodium of a sports drink. It is engineered for
illness and severe fluid loss, not for taste over an hour of running.

So if you are recovering from a stomach bug, a sports drink is the wrong tool
and a pharmacy rehydration sachet is the right one. If you are drinking one at
your desk because it says hydration on the bottle, plain water does the same job
for 125 fewer calories.

## Why the app still gives it 1.05

500 ml logged becomes 525 ml toward the goal. The 5% reflects two things. The
sugar and the modest sodium slow gastric emptying slightly compared to water.
And people finish a flavoured drink more readily than a plain one, so the
bottle actually gets emptied. It is a small bonus, not a claim of superiority.
The place a sports drink genuinely wins is long, sweaty sessions where the
carbohydrate and the sodium are both the point. There the app's larger 500 ml
default serving matches what you would really drink.

## Source

Hydration factors follow the Beverage Hydration Index. Maughan RJ, Watson P, Cordery PA, et al. “A randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index.” American Journal of Clinical Nutrition, 2016;103(3):717-723. https://pubmed.ncbi.nlm.nih.gov/26702122/

Page: https://waterchamp.app/drinks/sports-drink/