It was in the 1960’s when dietary carbohydrates were discovered as the major energy source to fuel exercise by being stored in the muscles as glycogen. Muscle glycogen content is linked to endurance performance and starting with lower concentrations results in premature fatigue, therefore nutritional strategies to increase muscle and liver glycogen before competition are common to maximise performance. Here we look at effective carbohydrate loading strategies to get the most from your diet and fuel your next event.

 

How long to load?

Sufficient muscle glycogen levels can be achieved from 24-48 hours of carbohydrate loading. Events lasting between 90 minutes and 3 hours require just 24 hours of loading, and then anything longer than that should be applied for 48 hours prior.

 

How much carbohydrate?

Again this will depend on the duration of the event, but training status should also be considered. For example an elite Tour de France cyclist will consume on average 10-12g carbohydrate per kg body mass per day, but somebody running their first half marathon will not need this much. So for a 90 minute race, 6-8g per kg body mass of carbohydrate is adequate the day before. For marathons and ultra-endurance events 8-10g·kg·bm is advised.

For example:

A 70kg athlete running a marathon will require at least 560g (8g·kg) carbohydrate. This is the equivalent to 9 large potatoes, 750g raw pasta or 17 ½ 500ml bottles of Lucozade sport.

Here's a guide for how to plan your nutrition in the hours before a marathon.

 

What type of carbohydrates?

As you can see it’s a lot of carbohydrates that need to be eaten and eating that much pasta or potatoes is not recommended. It’s important to eat foods that can be better absorbed by the muscles and will not cause gastrointestinal discomfort. Not all carbohydrates do this.

The glycaemic index (GI) determines the effect a certain food has on blood glucose with high-GI foods being broken down much quicker during digestion than low-GI foods, and are absorbed by the muscles more effectively.

Foods with a high glycaemic load (GL) have a greater quantity of carbohydrates for a given weight of food, and together with GI allow your muscles to efficiently obtain more carbohydrates. Large intake of fibrous (typically low-GI) foods can lead to gastrointestinal discomfort so it may also be wise to focus on simple, low fibre foods to alleviate digestive issues. White potatoes are high-GI and GL and removing the skins reduces the fibre content, making mashed potatoes an ideal choice when carb-loading.

 

Pre-race meal

Typically breakfast, your pre-race meal should prioritise easy to digest carbohydrates with ample protein and plenty of fluids. This can be personal preference, but a bowl of porridge with honey and banana is a good choice. Choosing lower-GI foods may actually be better in the hours before a race to help maintain satiety, and research also suggests that it may enhance performance compared to high-GI carbs.

Timing and quantities, again, are down to the individual, however it would be practical to eat 1-4 hours prior to racing, containing 1-4g·kg carbohydrate (1g·kg·hour).

 

Things to avoid

As well as fibre there are other nutrients to limit…not only preventing unwanted digestive discomfort, but also to allow for the increased calorie intake from carbohydrates alone. Dietary fat is very calorie dense and should be significantly reduced, but protein should also be limited to approx. 1.2g·kg. Fat and protein can also slow down digestion of carbohydrates therefore excessive intake can have a negative impact.

Other things to avoid include alcohol for obvious reasons, but also spicy food as this can cause major gut problems like bloating and wind which you do not want whilst racing! Excessive fructose (fruit sugar) may also cause flatulence, bloating and pain and should be monitored closely if you have ever experienced such unexplained issues.

Gluten and lactose containing foods may also be limited/removed from the diet for any individuals with specific intolerances, or if you don’t regularly consume them anyway, it’s better not to introduce them in large quantities just before competition!

 

Practical considerations

Hydration is fundamental during carb-loading because carbohydrates require water to get into the muscles. Drink plenty of fluids throughout the day especially with meals to aid absorption, but also to boost performance on race day.

It’s also important to note that any athlete should practice any nutritional strategy before applying them for a major competition. This is the same for carb-loading. Consuming foods that your body is not used to can have a negative effect. If you normally have porridge with skimmed milk before training, why would you choose a bowl of chocolate cereal with full fat milk before a race? You wouldn’t. Stick to foods you know and have practiced with before in the days/hours before a race to prevent unexpected digestive complications.

Whether you’re used to consuming such high volumes of food or not, getting carbohydrates in liquid form is much easier on the stomach and promotes hydration, whether it’s an electrolyte drink or a smoothie. 

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