How to carboload?


In the « How To ? » section, we take the best of sport science and translate it into practical nutrition for endurance athletes.

A decent running race needs to have a pasta party the day before, right ? So, you sign up for it, stuff yourself up in overcooked fusilli with watery tomato sauce and allow yourself a second serving of apple mousse. Then, after this collective carboloading ritual, you head to bed, feeling ready for the race.

But is a pasta party the best (=science-proven) way to carboload? Should we even carboload and if yes, how?

On the menu today : a weird Swedish diet, tapering and lots of bananas.


1. What’s the point of carboloading?

The glycogen in our muscles (and to some extent in our liver) is the preferential fuel used during high intensity exercise. A shortage of it induces a shift towards lipid oxidation, which, in the end, slows you down.

The overall idea of carboloading is to find an appropriate nutritional strategy to elevate these levels of muscle glycogen. In the end, this increases the time during which one can perform high intensity exercise.

While 100g of muscle would normally contain about 1-2 g of glycogen, an appropriate nutrition plan can increase this value to 4-5 g (!) and has been repeatedly linked with an increase in endurance performance (mostly by increasing a variable called “time to exhaustion”).


2. Which races should we carboload for?

For short races (<60 minutes), there is logically no benefit of carboloading, because a balanced diet should result in enough muscle glycogen to fuel such efforts.

Longer high-intensity events (half-marathon, marathon, triathlon of all sorts), however, deplete glycogen stores. Thus, carboloading helps delay glycogen exhaustion and helps sustain a high intensity during the race.

For ultraendurance events, it is still unclear whether there is any benefit of carboloading on performance. We will for sure discuss nutritional strategies for ultras in future articles!


3. What is the best carboloading protocol?

To answer this, we need a bit of sport science history.

Version 1: The “Swedish” diet

In the end of the 60’s, scientists in Sweden found out that a high-carbohydrate diet given for 3 days after strenuous exercise increased muscle glycogen levels above the baseline values (up to 4 g/100 g muscle instead of 1 or 2 g/100g – Bergström et al, Nature 1966). As a scientist, I have to say that this probably is one of the most poorly-designed study that got published in « Nature » (only 2 subjects, no control group with a low-carbohydrate diet, …). But, well that was 1966!

The authors concluded that a complete depletion in glycogen is needed to allow a full replenishment of the muscles later on. So, they went on to design a protocol in which a high training load coincides with a diet rich in proteins and fats for 3 days (day -6 to day -3 before the competition). This period is followed by 3 days in which a low training load coincides with a high carbohydrate diet (day -3 to competition day).


Even if athletes like to suffer, it’s needless to say that a combination of high-intensity exercise with a diet very low in carbohydrate had a negative physical and psychological impact. Inability to perform well and reports of perceived fatigue shortly before a competition were the major drawbacks of this method.

Version 2: The tapering protocol

Later on, American scientists tried to remove this painful phase from the carboloading protocol. They realized that no prior glycogen depletion of the muscles was required to reach high glycogen levels after 3 days of a high-CHO diet. Based on this study, a new carboloading protocol was set up. It combines the progressive reduction of training load (« tapering ») 6 days before the competition with a high carbohydrate diet starting 3 days before the competition (Sherman et al., Int J Sports Med, 1981).


Today’s version: The one-day protocol

While the tapering protocol was a great improvement over the Swedish diet, there was no scientific reason to think that 3 days was the right duration of exposure to a high-carbohydrate diet. Researchers in Australia (Bussau et al., Eur J App Physiol 2002) found that glycogen levels were already maximum after 1 day of a high-carbohydrate diet (10 g of carbohydrate / kg of body weight) in trained individuals that remained inactive during this time. There were no further improvements after 3 days.


Although we still can’t be sure that this is absolutely the most-optimized carboloading protocol, it remains to date the easiest protocol that has been scientifically shown to induce high muscle glycogen levels.

(For this section, graphs were adapted from S. Mettler Sports Nutrition lecture, ETH Zurich)


4. Practically, how do we do this?

Let’s get practical. To reach 10 g of carbohydrate / kg of body weight, how do we do this?

For a man of about 70 kg, that means 700 g of carbohydrate in a day, or roughly 2,800 kcal just from carbs. This represents about twice as more carbs than the same man would eat on a regular basis.

While there is not one single perfect protocol when it comes to choosing the food you will eat on your carboloading day, here are a few consensual rules:

1/ Scan food labels and count grams of carbs. I know it’s tedious, but it’s just one day. I use to simply take notes of what I eat on my phone and sum the carbs until I reach my goal. If you are unsure about the carb content, check the FDA Food composition database to find out.

2/ Snack. It may be difficult to reach the carboloading goal just during regular meals. Thus, snacking helps you get more carbs in.

3/ Drink. You may experience difficulties in reaching your carb target just by eating real solid food. Consider using fruit juices, sports drinks or maltodextrin-based carboloaders.

4/ Choose foods that are low in fats and proteins. This limits the total calorie intake.

5/ Go for the food you like and the food you know. Don’t try new things.


Concretely, here is an example of a carboloading day for a 70 kg athlete.


  • 150 g of muesli with dried fruits
  • 1 banana
  • 1 big glass of orange juice

Snack 1:

  • 500 mL of maltodextrin drink


  • 200 g of rice + meat and cooked veggies
  • 200g of low fat yoghurt with 1 banana

Snack 2:

  • Toasts with honey
  • 1 glass of fruit juice
  • 1 big cereal bar

Dinner (could be your pasta party)

  • Pasta with tomato sauce
  • 1 glass of sweet drink
  • Apple mousse

Snack 3:

  • 1 cup of hot chocolate
  • 1 cereal bar

TOTAL : 700 g carb / 150 g protein / 80 g fat / 4000 kcal

5. Can I calculate the exact quantity of carbs I need for a particular race?

The carboloading protocols tested in the scientific literature were optimized to get maximal muscle glycogen levels. But do we really always need the maximum muscle glycogen levels?

Probably not. The amount of glycogen you need for a particular race depends on a variety of factors: the duration of the race, your target time, your level of fitness, etc… Enough glycogen is enough to fuel certain races, or even to fuel marathons, provided that you run at an intensity that does not require too much carb.

Some people have tried to come up with computer models to predict the amount of carbohydrates you need pre-race to achieve a certain marathon time without hitting the wall. I’ll come back to these computer models another day in the Science section of this blog. But click here to estimate the amount of carbs you need before and during a marathon based on your target time and your fitness levels. Remember it’s just a computer estimation…




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