The 10 mistakes that ruin your race fueling: the scientific principles for optimizing your nutrition strategy

In an endurance race, performance depends not only on physical condition, training level, or equipment used. The ability to maintain an appropriate energy intake throughout the effort is a decisive factor, particularly when the duration exceeds 90 minutes.

During prolonged exercise, several factors progressively limit performance: depletion of muscle and liver glycogen stores, dehydration, disruption of electrolyte balance, central fatigue, and the onset of gastrointestinal problems.

Yet many endurance athletes compromise their performance not because of insufficient training, but because of a poorly managed fueling strategy: insufficient carbohydrate intake, poor digestive tolerance, lack of planning, or inappropriate use of energy products.

Competition nutrition should therefore leave nothing to chance. It should be individualized, tested in training, and adapted to the physiological demands of exercise.

Here are the 10 most common mistakes that can limit your performance on race day.

1. Starting to eat too late: the “emergency fueling” mistake

One of the most common mistakes is waiting for the first signs of fatigue before consuming carbohydrates.

When the feeling of reduced energy appears, the metabolic situation has already deteriorated: blood glucose may fall, glycogen stores are heavily taxed, and the ability to maintain intensity decreases.

During prolonged exercise, the brain relies heavily on circulating glucose. Reduced carbohydrate availability increases perceived exertion and may lead to an involuntary decrease in intensity.

Recommended strategy

Start carbohydrate intake from the early stages of exercise, generally after 20 to 30 minutes depending on the intensity and planned duration.

The goal is not to correct an energy deficit, but to prevent it from occurring.

2. Underestimating your carbohydrate needs

Carbohydrates are the main energy substrate during moderate- to high-intensity efforts.

Current recommendations have evolved considerably: modern strategies are no longer limited to avoiding “hitting the wall,” but seek to maximize energy availability during exercise.

Consensus recommendations indicate:

• 30 to 60 g of carbohydrates/hour for efforts lasting 1 to 2.5 hours;
• 60 to 90 g/h for prolonged efforts;
• up to 120 g/h in athletes specifically trained to tolerate high intakes.

This increase is possible thanks to the use of different intestinal transporters:

• glucose primarily uses the SGLT1 transporter;
• fructose uses GLUT5.

The glucose-fructose combination thus makes it possible to increase exogenous carbohydrate oxidation and exceed the absorption limits of a single type of sugar.

Common mistake

Consuming only one gel per hour during an ultramarathon when the body sometimes requires two to three times more energy.

3. Neglecting digestive training ("gut training")

The digestive system is not a fixed factor: it adapts to the demands placed on it.

Many athletes limit their intake during training for fear of digestive problems, then try to significantly increase their consumption on competition day.

This approach is counterproductive.

Digestive training notably helps to:

• improve gastric emptying;
• increase intestinal absorption capacity;
• improve tolerance to high carbohydrate intake.

Practical application

Gradually test your intake during long sessions:

• increase the amount of carbohydrates per hour;
• vary the textures;
• reproduce race conditions.

4. Choosing an energy product without considering its composition

Not all energy gels meet the same needs.

The choice should depend on:

• duration of the effort;
• intensity;
• digestive tolerance;
• whether or not caffeine intake is needed.

A few differences:

Gel mainly based on glucose/maltodextrin

Advantage:

• rapid absorption;
• good energy availability.

Glucose-fructose gel

Advantage:

• greater absorption capacity;
• useful during long efforts.

Caffeinated gel

Advantage:

• possible improvement in alertness;
• reduced perception of effort.

However, caffeine should be tested because individual responses vary greatly.

5. Drinking only water during prolonged exercise

Water is essential, but it does not replace the electrolytes lost in sweat.

Sodium plays several roles:

• maintenance of plasma volume;
• fluid balance;
• nerve transmission;
• muscle contraction.

Excessive consumption of water low in sodium during prolonged exercise may contribute to the development of exercise-associated hyponatremia.

The right strategy

Adjust fluid intake according to:

• their sweating rate;
• the temperature;
• the duration of the run;
• the sodium concentration of their sweat.

6. Consuming too much fiber, fat, or protein before and during exercise

During intense exercise, digestive blood flow decreases in order to prioritize the muscles and thermoregulation.

Some foods then become more difficult to digest:

• foods rich in fiber;
• very fatty meals;
• large amounts of protein.

This increases the risk of:

• bloating;
• reflux;
• abdominal pain;
• diarrhea.

Before the race

Prioritize:

• easily digestible carbohydrates;
• low fiber content;
• low fat content.

7. Not adapting your strategy to environmental conditions

The same nutrition strategy does not work in all conditions.

Heat causes:

• increased cutaneous blood flow;
• increased sweating;
• faster dehydration;
• decreased digestive tolerance.

In the mountains, altitude can also alter the perception of effort and energy needs.

Fueling must therefore evolve according to:

• temperature;
• humidity;
• altitude;
• planned duration.

8. Copying an elite athlete's strategy

An elite athlete's nutrition strategy is often based on:

• a high training volume;
• specific digestive adaptation;
• a different body mass;
• years of experimentation.

An amateur runner does not necessarily have the same needs or tolerance.

The best strategy is the one that matches your physiology.

9. Not quantifying your intake

A common mistake is to rely solely on "feel."

However, two gels can provide very different amounts depending on their composition.

To improve, it is useful to know:

• grams of carbohydrates consumed per hour;
• amount of fluid consumed;
• amount of sodium provided;
• digestive tolerance.

This approach allows you to gradually refine your strategy.

10. Forgetting recovery immediately after the race

Fueling does not stop at the finish line.

After prolonged exercise, the goal is to:

Restore glycogen

The first hours after exercise are a favorable period for muscle glycogen resynthesis.

Promote muscle repair

Consuming protein with sufficient essential amino acids promotes muscle protein synthesis.

General recommendations are around:

• 20 to 40 g of protein after exercise, depending on body size and training load.

Conclusion

Effective fueling is not simply a succession of gels and energy drinks. It is a genuine physiological strategy aimed at maintaining energy availability, limiting dehydration, preserving digestive comfort, and optimizing recovery.

The best performances are often achieved through attention to detail: starting your intake early enough, reaching an appropriate amount of carbohydrates per hour, training your digestive system, and personalizing your strategy according to your constraints.

As with training, competition nutrition should be prepared several weeks before the goal event. On race day, there should be no more experimentation: you must apply a strategy that has already been validated.