# Osmolality in sports drinks: why concentration decides what your stomach does

> It is not the amount of carbohydrate that upsets the stomach but its concentration. What research shows about gastric emptying, high-molecular-weight starch and dosing - and how WOO® Fast Endurance Lemon is set up.

Most gastrointestinal trouble in endurance sport has nothing to do with the amount of carbohydrate and everything to do with its concentration. Anyone who has ever climbed a hill with a sloshing stomach has experienced osmolality first hand - without knowing the term.

## Osmolality: the underrated variable

Osmolality describes how many dissolved particles sit in a fluid. The more particles, the slower a drink leaves the stomach and the more strongly it pulls water into the gut. Vist and Maughan (1995) showed in humans that gastric emptying is governed by both carbohydrate content and osmolality - and independently of one another. In practice: two drinks with identical carbohydrate loads can feel completely different depending on which molecules those carbohydrates are made of.

## High-molecular-weight starch: much energy, few particles

This is the trick of long-chain carbohydrates. A single molecule of high-molecular-weight maize starch carries many glucose units yet counts osmotically as just one particle. That allows high energy density to be paired with **low osmolality**. Leiper and colleagues (2000) found faster gastric emptying for a high-molecular-weight glucose polymer than for conventional solutions, and Piehl Aulin and colleagues (2000) additionally showed a higher glycogen resynthesis rate after exercise. Short-chain carbohydrates still belong in the mix because they are available immediately.

## Heat, sweat and sodium

In summer the equation shifts. Baker (2017) summarised that sweat rates range from 0.5 to more than 2.0 litres per hour depending on person and conditions, and that sweat sodium concentration varies strongly between individuals. Ride for two hours at 28 degrees and you lose relevant amounts of sodium - plain water then only dilutes what is already scarce. Magnesium **contributes to normal muscle function**.

## Dosing instead of guessing

This is exactly where the box plays its strength. Recommendations for carbohydrate intake are quantity-based: Jeukendrup (2014) outlines 30 to 90 g per hour depending on duration and intensity. Those numbers are only actionable if you know how much is actually in the bottle. A single-serve sachet is a fixed quantity: no scoops, no estimating, no drifting concentration. For training the gut, reproducibility is the precondition.

## How WOO® Fast Endurance Lemon is set up

**[WOO® Fast Endurance Lemon](/en/shop/woo-fast-endurance-lemon-box)** combines high-molecular-weight maize starch with maltodextrin, glucose and sucrose. One sachet holds 60 g and supplies 56.1 g carbohydrates, of which 27.7 g sugar, 230 kcal, 300 mg sodium and 25 mg magnesium. The box contains ten sachets, meaning ten identically dosed units - enough for a full training block. The lemon flavour is the tart, fresh pole of the range and goes down more easily in warm conditions than sweeter variants, which matters by the third bottle of a hot afternoon. WOO® Fast Endurance is vegan, gluten- and lactose-free and free from artificial additives.

## Frequently asked questions

**How much should I drink per hour?**
Carbohydrate intake follows duration and intensity, not thirst. One sachet per hour is a good starting point for long sessions, and the dose can be adjusted individually.

**Why sachets instead of a tub?**
Because a fixed portion keeps the concentration constant. Only if you always mix the same way can you compare tolerance and effect at all - and in a pack the sachet is more practical.

**Is this useful for shorter sessions too?**
Under 60 minutes the body generally needs no external carbohydrate. From 90 minutes it becomes relevant, and earlier in the heat.

## Sources

Vist GE, Maughan RJ (1995), Journal of Physiology - Effect of osmolality and carbohydrate content on gastric emptying of liquids in man.
Leiper JB et al. (2000), Scandinavian Journal of Gastroenterology - Improved gastric emptying rate of a unique glucose polymer with gel-forming properties.
Piehl Aulin K et al. (2000), European Journal of Applied Physiology - Muscle glycogen resynthesis rate with carbohydrates of low and high molecular masses.
Baker LB (2017), Sports Medicine - Sweating rate and sweat sodium concentration in athletes.
Jeukendrup AE (2014), Sports Medicine - A step towards personalized sports nutrition: carbohydrate intake during exercise.

*WOO® Fast Endurance Lemon Box in the NEMAPO shop.*