What is carb loading?

Confused about carb loading? Bupa sports dietitian Nick Green explains what it is, how to get it right, and what a typical carb loading daily diet might look like.

Carb loading refers to eating more carbohydrates than usual in the week before an endurance event, such as a long-distance run, swim, or cycling race. When done correctly, it can help maximise the amount of fuel (in the form of glycogen) stored in your body to help you go further, faster and more efficiently.

“Effective carb loading is predicted to have a two to three per cent performance improvement,” Bupa sports dietitian, Nick Green, explains. “Which may not sound like much but may be enough to shave five minutes off your marathon PB [personal best].”

Why are carbs so crucial?

The carbohydrates in foods like fruit, vegetables, rice, pasta and bread, are all digested and broken down into glucose—the main form of energy that our body and brain uses to function. Excess glucose is stored in our muscles and liver in the form of glycogen. Glycogen can then be converted easily back into glucose when the body needs it, circulated around our bodies in our blood, metabolised in our cells and muscles, and converted to energy.

Whenever we exercise, but especially when we’re training for an endurance event, we’re using up a lot of glucose and then once that’s gone, the stored glycogen. If our body runs out of glycogen, it turns to the next best high-energy fuel source, fat. However, our bodies have to work a lot harder to break down fat.

“This can lead to you feeling flat during your workouts, meaning you’ll enjoy them less and it may contribute to you giving up,” Green explains. “And if you’re not having those carbohydrates after your workouts, you may not be recovering well, and not replenishing your muscle fuel stores—your glycogen stock.”

When it comes to race day, we want to ensure that our bodies make efficient use of our glycogen stores, and minimise the amount of fat it has to burn for energy. That’s where carb loading comes in.

“The purpose of carbohydrate loading is to maximise your muscle glycogen [fuel] stores,” Green explains. “This is achieved by following a high carbohydrate diet for one to four days before the event, during a period of exercise taper.”

How do I carb load appropriately?

Carb loading is not an exact science, and is very much dependant on everyone’s individual body. But the Australian Institute of Sport does have some general recommendations.

Start your carb loading approximately four days before race day and increase the amount of carbohydrates you’re consuming to about 7 to 12 grams per kilogram of body weight. So if you weigh approximately 70 kilograms, you should consume 490 to 840 grams of carbohydrates per day for the final four days before a race.

It’s important not to take this as an ‘I can eat anything’ pass. While you need to increase your carbs, you still need to ensure your meals remain healthy, balanced, and in particular, low in fat and fibre to allow you to consume the extra carbohydrates you need.

“While increasing your carb intake, it’s important to choose low fibre options, otherwise you may end up with an upset stomach or even fail to consume enough carbs as the meals are too heavy and take longer to digest,“ Green explains.

Low fibre cereal with low fat milk and a glass of orange juice

It can be a challenge to get it right. So working with a sports dietitian or using a carbohydrate counter can really help. Below is an example of what a typical daily carb loading diet might look like for someone who weighs about 70 kilograms (kg):

Breakfast

2 cups of low-fibre cereal (less than 1.5g of fibre per serve)
1½ cups low-fat milk
40g dried fruit
1 glass of fruit juice

Morning tea

200ml tub low-fat yoghurt
1 cup tinned fruit (with syrup)

Lunch

Sandwich: 3 slices white bread with 2 slices of lean meat, and salad filling of your choice
60g dried fruit

Afternoon tea

1 piece of fruit
600ml sports drink

Dinner

1½ cups of white rice or pasta, cooked
100g chicken (skinless breast fillet)
1 cup of tomato based sauce
1½ cups mixed vegetables (e.g. grated carrot/zucchini, chopped mushrooms and celery)

Snack

2 crumpets
1 tablespoon of jam
1 glass of fruit juice

This example provides approximately 500 grams of carbohydrates (7.1g/kg body weight). And Green has developed similar plans for people who weigh approximately 60 kilos and 80 kilos here.

Finally, don’t forget to taper your training at the same time. This is a crucial part of carb loading that many athletes can forget. If you continue training hard right up to race-day, your carbohydrate loading could go to waste. You may end up using too much of the extra glycogen in your training to allow your body to store enough of it up to make a difference on race-day.

If you’re keen to find out more about what tapering is, check out our article.

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