The instruction on every energy gel packaging — "take with water" — is not a precaution. It is physiologically mandatory. An athlete who regularly takes gels dry, or washes them down with a sports drink, is making a mistake that goes beyond taste preference. The osmolality mismatch between a concentrated gel and intestinal fluid is a direct cause of the GI distress that ends endurance performances.
---
Osmolality: The Core Concept
Osmolality is a measure of solute concentration in a solution, expressed in milliosmoles per kilogram (mOsm/kg). The human body maintains plasma osmolality in a tightly regulated range of 275–295 mOsm/kg. Fluids and foods that enter the digestive tract must approach isotonic (approximately 300 mOsm/kg) to move efficiently through the GI system without disrupting fluid balance.
A standard energy gel — concentrated maltodextrin and sugar — has an osmolality of approximately 600–900 mOsm/kg. That is two to three times the concentration of blood plasma.
---
What Happens When You Take a Gel Dry
When a hypertonic gel enters the small intestine without diluting fluid:
1. Osmotic fluid draw. The intestinal wall responds to the high-concentration bolus by drawing water from the bloodstream and surrounding tissue into the intestinal lumen — attempting to dilute the solution to isotonic. This is the opposite of the absorption process. Net fluid movement is *into* the gut, not out of it.
2. Gastric emptying slows. The stomach's duodenal osmoreceptors detect a hypertonic solution and throttle the rate of gastric emptying to prevent the small intestine from being overwhelmed. This delay — lasting 15–30 minutes — means the carbohydrate from the gel reaches the bloodstream significantly later than intended.
3. Intestinal distension and cramping. The accumulated fluid in the intestinal lumen creates distension, triggering peristaltic cramping. The bloating and "side stitch" commonly reported after taking gels are often osmolality-driven rather than running mechanics-related.
4. Nausea. Persistent osmotic imbalance in the gut activates vagal nausea pathways — the same protective mechanism that produces nausea from eating too much, too fast. In the context of racing, this is frequently misattributed to effort or heat rather than its actual cause: a concentrated carbohydrate bolus in an inadequately hydrated GI environment.
---
Why Sports Drink Is Not a Substitute
A common error is washing down a gel with a sports drink rather than water. Sports drinks typically contain 4–8% carbohydrate, corresponding to osmolalities of approximately 200–400 mOsm/kg. Adding this to a gel bolus *increases* the total carbohydrate concentration in the stomach relative to taking the gel with water alone — amplifying the osmotic load, not resolving it.
At aid stations where only sports drink is available:
- Take the gel approximately 10 minutes before the aid station
- Use water to dilute — if sports drink is the only option, drink additional water from a carried bottle or dilute the sports drink
- Avoid stacking gel + sports drink as a combined bolus
Isotonic Gels: The Alternative Engineering Approach
Some gel formulations — notably SiS Go Isotonic — are pre-formulated at isotonic concentration (approximately 280 mOsm/kg) using a lower carbohydrate concentration and larger gel volume (~60mL vs ~30mL for standard gels). The trade-off:
- Isotonic gels can be taken without water
- Lower carbohydrate density (~22g vs 25–40g for concentrated gels) means more gels required per hour at high carb rates
- Larger volume per serving may be harder to carry in high quantities
---
The Minimum Fluid Protocol
For standard hypertonic concentrated gels, the minimum fluid recommendation from sports gastroenterology is 150–200 mL of water per gel — sufficient to dilute the concentrated bolus to approximately isotonic in the stomach before duodenal emptying.
Timing: fluid should be consumed simultaneously or immediately after the gel — not 2–3 minutes later — to allow mixing in the stomach before gastric emptying begins.
For athletes building a fuelling plan that accounts for fluid requirements at each gel — and calculating the total water they need to carry between aid stations based on their gel schedule — the energy gel calculator at winsport.uk/tools/nutrition/energy-gel-calculator shows fluid requirements per gel alongside the full timed fuelling schedule.
In races where GI distress is most common — has the issue been gel timing, taking gels without adequate water, or stacking gels with a sports drink at aid stations?