Carb loading: What, when, and how to fuel a big swim

Carb loading is especially useful before long endurance events that last over 90 minutes, such as marathons, long-distance swims, or cycling races, where your body relies heavily on stored energy. Health and fitness coach Vivienne Rickman is your guide.

Carb loading might sound complicated, but it’s actually a simple nutritional strategy to make sure you have enough energy to go the distance – without running out midway through. It’s especially useful before long endurance events that last over 90 minutes, such as marathons, long-distance swims, or cycling races, where your body relies heavily on stored energy. If your event is shorter than 90 minutes or less intense, you probably don’t need to carb load. But for anything long and steady, especially over two hours, it can help you keep going for longer.

What is it?

Carb loading is a way to fill up your body’s energy stores before a big endurance event. Your muscles rely on glycogen, which comes from carbohydrates, for fuel. The more glycogen you have stored, the longer and stronger you’ll be able to perform. Without enough, you’re more likely to feel tired, heavy, or hit what’s often described as “the wall.”

For any swim likely to involve over two hours of sustained effort, carb loading can help you stay fuelled, maintain your technique, and reach the finish feeling strong – instead of completely wiped out.

When to do it

Start carb loading one to three days before your swim. This gives your body time to top up its energy stores properly. You don’t need to eat more calories overall – just shift your meals to include more carbs and slightly less protein and fat. Aim for a higher carb intake than usual (around 10 grams of carbohydrate per kilogram of body weight per day), but increase gradually to avoid feeling bloated.

It’s also a good time to ease off training (tapering) this allows your body to rest and store all that extra fuel.

What to eat

Stick to foods you know and trust – things your body handles well. Good options include familiar easy-to-digest carbs such as rice, pasta, noodles, potatoes or sweet potatoes, as well as bread products, cereal or porridge, bananas, berries, or dried fruit and drinks such as fruit juice, smoothies, and sports drinks.

You don’t have to go overboard with pasta and pizza every night, just shift the balance of your meals toward carbohydrates. Smoothies and juice are also helpful for increasing your carb intake without making you feel overly full.

Try to keep fibre and fat on the lower side, especially if you have a sensitive stomach. The goal is to feel energised, not bloated or sluggish. That said, don’t cut out protein and healthy fats entirely, they still help support your muscles and aid recovery.

The day before your event

This is time to relax and focus on staying calm and well-hydrated. Keep your meals centred around carbohydrates, but don’t go overboard, today is about steady fuelling, not overloading. A pasta or rice-based dinner is ideal, eaten earlier in the evening to give your body time to digest before bed.

Drink water throughout the day (electrolyte drinks can be helpful, too), but there’s no need to go over the top and find yourself running to the loo every five minutes!

Event day!

Eat something around 2–3 hours before your swim. Keep it light, carb-rich, and easy to digest, porridge with honey and banana, toast with jam, or a smoothie with oats and fruit are all great options.

Feeling nervous and not very hungry? Totally normal. If that’s the case, go for something small, like a banana and a sports drink. You just need a little something to top up your energy before you get in the water.

Practice makes perfect

If carb loading is something you plan to use, it’s a good idea to practise it during your training. That way, you’ll know what works for your body, and what doesn’t, well before event day.

Fuel well, and you’ll give yourself the best chance to feel strong, steady and confident in the water.