When is carb loading actually needed?

Joëlle Flück 14. March 2023

Foto: iStock.com/Olha_Afanasieva

The purpose of carb loading is to maximise the carbohydrate stores in your muscles for longer loads. By increasing the supply of carbohydrates beforehand, more energy in the form of carbohydrates is available during the load. But which competitions actually need this? Or is it always needed?

Presented by Swiss Sports Nutrition Society

In general, there are two different ways in which your carbohydrate stores can be replenished. One method generally involves replenishing the carbohydrate stores before a competition, so as to fill them as much as possible. However, the duration of the competition should be such that no drop in performance is to be expected even if the stores are not optimally filled. This is the case for a 5K or a 10K run, for example. So-called carb loading, on the other hand, not only aims to just fill up the carbohydrate stores, but also maximise them. It is mainly used in competitions where the carbohydrate stores are expected to become (almost completely) depleted. This is then directly linked to performance. A marathon or an ultra trail could be examples here.

Carb loading for long competitions (e.g. marathon, ultra trail)

Carb loading involves adapting your training and diet to maximise the storage of carbohydrates in your muscles (muscle glycogen storage) before (endurance) competitions. In this way, the carbohydrate intake is maximised for 48 to 72 hours while the scope of training is reduced at the same time. This means that a total of 10 to 12 g of carbohydrates per kg of body mass are consumed over a 24-hour period. For an athlete weighing 70 kg, this is around 700 to 740 g of carbohydrates per day. Put differently: 1 kg of uncooked pasta spread over an entire day! It soon becomes clear that this is an extreme amount and requires a lot of planning. To avoid triggering digestive problems, low-fibre food is essential. It is also worth spreading the amounts over various meals and snacks.

Possible daily routine for an athlete weighing 70 kg (10 to 12 g CHO/kg/day) for the last 2 days before the race

  • Breakfast: 1 glass of water, 2.5 dl orange juice, 2 slices of bread, honey, 60 g of oatmeal, 1 piece of fruit, 1 plain yoghurt
  • Snacks: 1 energy bar, 1 carbo-loader or sports drink (approx. 70 g of carbohydrates)
  • Lunch: 1.5 plates of pasta with tomato sauce, a little grated cheese, 1 small serving of vegetable soup, 1 small slice of bread, 1 glass of water
  • Snack: 1 carbo-loader or sports drink, 1 banana or 1 slice of white bread with a little honey
  • Dinner: 1 large serving of rice, steamed carrots, 120 g of chicken breast or tofu, 1 small serving of vegetable soup + 1 small slice of bread, 1 glass of water
  • Late snack: 1 carbo-loader or 6-8 dl sports drink

Pre-competition diet for a 5K or 10K race

For endurance competitions with a duration of less than 90 minutes, carb loading is neither necessary nor productive. The duration of the competition is too short, which means depleted carbohydrate stores are not a performance-limiting factor. This method mainly involves eating a carbohydrate-rich diet in the last 24 hours before the race. Around 7 to 12 g of carbohydrates per kg body mass would need to be eaten during this period based on individual needs. For a 5K race, the lower recommended amounts would thus be appropriate.

In contrast to carb loading, this means you can get by with three carbohydrate-rich main meals as well as carbohydrate-rich snacks (e.g. 1 piece of fruit, 1 energy bar, 1 slice of honey bread, 1 pack of cereal crackers or a 500 ml sports drink) when preparing for a 5K or 10K run. You still need to make sure you drink enough fluids. This applies too:

  • Avoid fatty foods and excessive servings of protein.
  • Reduce your fibre intake to prevent gastrointestinal problems.
  • Drink plenty of fluids.

Special case: half marathon

A half marathon lies between these two recommendations, depending on your level of performance. While a half marathon does not generally require proper carb loading, it does need an increased carbohydrate intake in the last 24 hours before the race. In contrast to a 5K race, it is worth eating bigger main meals than you normally would as well as carbohydrate-rich snacks and 1-2 carbohydrate-enriched drinks at the most to ensure that your carbohydrate stores are sufficiently full at the start.

In practice, what are the most common mistakes?

Either the carb loading is done incorrectly (e.g. the overall intake is too low) or overlarge meals are eaten at once, which causes difficulties with digestion. Excessive sources of fat or protein or large amounts of fibre put an additional strain on the gastrointestinal tract. It is therefore important to test carb loading in the run-up to your target competition and use carbohydrate-rich fluids in addition to solid foods!