Carb-loading: What is it, and do we really need to do it before a marathon?

Carb-loading is a term you’re likely to have heard before, but what does it mean? Do we really need to jump on the carb-bandwagon in order to excel, or is it just another diet myth? Should you really have an ‘all-you-can-eat’ pasta dinner the night before the marathon?

An ariel shot of people running in a marathon

The science

“Our body stores carbs in the form of glycogen in our muscles and liver. When we workout, our body needs energy. The easiest accessible way for the body to regain this energy is through our glycogen stores – the body converts glycogen to glucose, which can be used as energy,” says Lisa Scheeper, nutritionist at Fresh Fitness Food.

“The body can also use fat as fuel to generate energy. This process is happening often simultaneously to burning glycogen, but this process is more complex and slower. It’s when our glycogen runs out that runners ‘hit the wall’. Beyond this point, the body can still use the fat metabolic pathway to produce energy, but this is about 15% less efficient. This is why, inevitably, the body will slow down.”

“On average, the human body can store between 350-500g of glycogen, equalling at around 90 minutes of endurance exercise,” Lisa explains.

Of course, carb-loading sounds great. Who doesn’t want a delicious bowl of pasta? But carb-loading is a total numbers game. Shorter distances (such as 5Ks or 10Ks) don’t require it because it is unlikely you’ll deplete the fuel in your muscles in the time it takes to run those races. It’s for the races that will take longer than 90 minutes, that these extra steps may need to be taken. It’s also important to remember that when making changes to your diet or lifestyle, professional support is advised.

Our bodies are unique and what works for one person, may not work for you, so seeking advice from a professional ensures you’re not only looking after your body, but you’re getting the most out of your training and ability.

Sophie’s Do’s and Don’ts

So carb-loading is one way to increase your glycogen storage to full capacity ready for race day, but how does carb-loading actually work?

“A frequent mistake made by runners is eating an extra large dinner the night before,” says Lisa. “The problem with this is that it doesn’t give your body enough time to digest, and you’ll still feel bloated in the morning. On top of that, you can’t completely fill your muscles with glycogen from just one meal.”

Lisa continues: “For this reason, it’s better to start choosing your carbs wisely three days prior to your race. Since you’re tapering and running every few miles over these final days, the glycogen will accumulate in your muscles.”

“Aim to keep your total calorie intake for the day in line with your normal intake, but swap fats for more carbs. Try to get around 70% of your intake from carbs. Go for healthy, unprocessed foods and leave the junk food out. It’s a good idea to scale back on fibrous foods the day before the marathon, as this could cause some discomfort in the gut whilst running.

“The night before the race, enjoy a normal sized, but carb-heavy meal. Don’t eat too late and give your body enough time to digest. You don’t want to wake up on race day full from the night before, it’s better to wake up hungry. Try to schedule your breakfast three hours before the start of the race.”

If this has made you hungry, don’t worry. Lisa has a great recipe, perfect for breakfast, lunch, dinner, or even as a pre-marathon meal.

Root Vegetable Rosti

Serves 1


  • 40g white potato, peeled and grated
  • 40g parsnips, peeled and grated
  • 40g carrot, peeled and grated
  • 1 white onion, sliced
  • 1 tsp chopped thyme
  • 1 tsp wholegrain mustard
  • 2 tbsp flour
  • Salt and pepper


Mix the ingredients together in a bowl, cover and leave for 10-15 minutes, or until the water comes out of the vegetables and the mix becomes sticky.

Place a medium-sized frying pan onto the heat and add 1 tsp of oil. Place the mix in the pan and push out to fill the pan. Cook on one side for five minutes, or until the rosti begins to colour. Carefully flip over and cook on the other side for a further five minutes. Serve.

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Written by Ellen Lees
Head of Content.
Written by Ellen Lees
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