The truth about carb loading

Loaves of bread and spreads on a table, viewed from above.

Let's clear up the carb controversy.

Unless you’ve been living on a desert island for the last decade, it’s likely that you’ve heard of carb loading.

But is gorging on a whole loaf of bread before going for a run really a healthy approach?

We chatted to Alex Dreyer, accredited Sports Dietitian, to set the record straight.

So, what is carb loading?

Carbohydrates are our body’s primary energy resource. They are broken down into sugar during digestion, which is then stored in our muscles as glycogen.

Our muscles store only enough glycogen to provide 90-120 minutes of high-exertion energy. So, the theory goes: the more carbs you eat, the more glycogen your body stores and the better you avoid fatigue.

But is carb loading the right strategy for everyone? If you’re doing the 4km, should your carbohydrate intake differ from that of a half marathon participant? In short, yes.

Let’s break it down in more detail.

For 4km participants and those walking the 12km:

Man and woman running in the HBF Run for a Reason 4km

Do I need to carb load?

Generally, carb loading is something only longer distance runners need to worry about.

Unless you’re doing multiple long training sessions per week (lasting 90-120 minutes), your carbohydrate intake doesn’t need to change.

Sorry to be the bearer of bad news – we know scoffing down that huge bowl of pasta is tempting!

Even the day before HBF Run for a Reason, you shouldn’t consume more carbohydrates than normal, as it will be extra bulk in your gut that you won’t use.

Focus instead on eating familiar foods and staying hydrated, as well as getting a good night’s sleep.

Are there certain types of carbohydrates I should be eating?

Not all carbs are created equal! Although you don’t need to carb load if you’re participating in a shorter distance, you should prioritise quality carbohydrates that will keep you full for longer. 

Aim to include wholegrain and high-fibre carbs in most meals, as well as carbohydrate-rich vegetables.

Think wholemeal bread and pasta, brown rice and quinoa, rolled oats, legumes, lentils, sweet potatoes and all fruit and veggies with the skin left on.

How much carbohydrate should I eat?

As an adult, you should aim for three to six serves per day, spread out over three meals and two snacks (you'll need more if you're pregnant or breastfeeding).

A serve is roughly equal to one slice of bread, half a cup of porridge, rice, or pasta, or three medium crackers.

For 12km and half marathon runners:

Two women on the half marathon course at HBF Run for a Reason

Do I need to carb load?

Good news – if you’re running in one of the longer distances, you can slide that gigantic bowl of pasta over!

Carbohydrate is your body’s primary fuel for hard exercise. Nourishing your body with high-energy food can increase your training volume and allow you to reach your potential in harder sessions.

Research suggests that fuelling with carbohydrates can improve your performance by anywhere between 2 per cenup to more than 10 per cent.

How much carbohydrate should I eat?

During training:
  • Pick out the 2-3 hardest training days in your week and aim to fuel as best as possible in the 24 hours before them.
  • Before these hard training days, aim to slightly increase the carbohydrate you have at meal times so that the body stores more fast-burning fuel and you can go longer without fatiguing.
  • Some examples: going from ½ cup to ¾ cup rolled oats in the morning, from ½ cup to ¾ or one cup of brown rice at lunch, and one baked sweet potato to one cup of wholegrain pasta at dinner.
Before event day:
  • In the two days before the race and the morning of, try the same strategy as outlined above. However, replace all wholemeal carbs with ‘white’ versions to avoid digestive discomfort.
  • Trade out the high fibre options with simple carbohydrates, like white sourdough bread, white rice and pasta, and quick oats or a low fibre cereal.
  • Remember that these aren’t the healthiest options, so go back to the higher fibre alternatives once the race is over.
On event day:
  • Take a carbohydrate rich snack with you to the start area the morning of the race. This could be a single slice of bread with jam, a muesli bar, or a small pack of sultanas or a handful of dates.
  • Consume this snack around 20 minutes before the start time, as this will get your blood sugar and energy levels up before the run.
  • Those running the half marathon could also consider using gels, chews, or liquids during the run, if you are planning to be running for 90 minutes or more. You shouldn’t need more than one gel (roughly 25-30g of carbohydrate).

Beware of the risks

Even if you are running in the 12km or half marathon, carb-loading might not be the best plan for you.

The high-energy diet doesn’t suit everybody and can cause some negative side-effects, especially if you have diabetes.

It’s a good idea to consult your GP or meet with an accredited dietitian to receive personalised advice.


This content is provided by Alex Dreyer, an accredited Sports Dietitian based in Perth.