Carbohydrate loading: when and how should you do it? Is it really essential?

As a major endurance race or goal approaches, many endurance athletes turn to a well-known nutritional strategy: carbohydrate loading (or "carb loading"). It promises to increase energy stores and delay fatigue, but is it really necessary for every race? Who is it for, and above all, how can it be applied effectively without risking the opposite effect?

In this article, we review what the science says, the mistakes to avoid, and the best practices for maximizing your performance on race day.

1) Why replenish glycogen stores?

Glycogen glycogen is the form in which the body stores carbohydrates, mainly in the muscles and liver. During prolonged endurance exercise, it is the body’s preferred energy source. The problem is that these reserves are limited.

On average, an athlete can store:

• Approximately 400 to 500 g of muscle glycogen, or 1,600 to 2,000 kcal,
  

• And 80 to 100 g of liver glycogen, or 300 to 400 kcal.
  

At moderate to high intensity, these reserves can be depleted in 1h30 to 2h. This is precisely where carbohydrate loading comes in: it allows these stores to be increased to their maximum, to maintain a high intensity for longer.

2) What the studies say

The research is conclusive: for prolonged endurance efforts, carbohydrate loading improves performance. A meta-analysis by Burke et al. (2011) showed an average gain of 2 to 3% during events lasting more than 90 minutes.

Other classic studies confirm this benefit:

• Karlsson & Saltin (1971) observed a significant improvement in marathon performance,
  

• Sherman et al. (1981) showed a prolonged time to exhaustion in cyclists who had followed a carbohydrate-loading protocol,
  

• Jeukendrup et al. (2000) demonstrated better power retention at the end of a long-distance triathlon.
  
  

But be careful: for efforts lasting less than 90 minutes, the benefits become negligible, or even counterproductive (temporary weight gain, digestive discomfort…).

3) When should it be implemented?

Carbohydrate loading is not a universal strategy. It should be used appropriately, depending on the goal and duration of the effort.

It is useful for:

• Events lasting more than 90 minutes : marathon, trail running, triathlon, cyclosportive…
  

• A series of long sessions (training camp, ultra, back-to-back).
  

• The goal of optimal performance at high intensity.
  
  

It is unnecessary, or even inadvisable, for:

• Short events (< 1h15).
  

• Regular training sessions.
  

• Periods of weight loss or strict calorie intake management.
  
  

4) How to load carbohydrates effectively? The modern protocol

The old methods were based on carbohydrate depletion followed by “refeeding.” Too demanding, these methods have largely been abandoned.

Today, the most effective and best-tolerated protocol is based on:

• A before the event, an increase in carbohydrate intake for 1 to 3 days
  

• Without a depletion phase,
  

• Combined with a gradual reduction in training volume.
  

As a general rule, recommendations suggest 8 to 12 g of carbohydrates per kilogram of body weight per day.

Example: for a 60 kg athlete → 480 to 720 g of carbohydrates per day.

This may seem like a lot… and it is! That is why it is important to prioritize easily digestible foods with a moderate to high glycemic index, while limiting fiber, fat, and protein.

5) Which foods should you prioritize?

Here are some ideal sources for achieving this goal:

The complex carbohydrates such as white pasta, basmati rice, semolina, and potatoes
The simple carbohydrates : applesauce, ripe fruit such as bananas, fruit juice, energy bars, carbohydrate drinks, powdered maltodextrin (easy to digest and measure)

However, avoid legumes, raw or high-fiber vegetables, fatty or overly protein-rich foods, as they slow digestion, as well as unfamiliar foods or foods not tested during training.

If you tolerate it, you can keep a small portion of cooked vegetables.

And don’t forget: the glycogen is stored with water (approximately 3 g of water for 1 g of carbohydrates). Hydration should therefore be increased (approximately 30 to 40 ml/kg/day), without overdoing it.

5) Common mistakes

1. Eating too much at once : it is better to spread carbohydrates throughout the day.
   

2. Forgetting to test the protocol during training : it is risky on race day.
   

3. Getting the quantities wrong : too little is ineffective, while too much can cause digestive problems.
   

4. Ignoring digestive signals : you should not force yourself to the point of causing disgust or nausea.
   
   

In summary

The final word

The carbohydrate loading is not a myth: it is a scientifically validated, solid strategy for improving performance during prolonged endurance efforts. You still need to know when and how to use it. When well planned, tested beforehand, and adapted to your specific needs, it can help you reach the next level… and perhaps avoid the dreaded “wall” during your next race.