Carb Loading For Runners: How To Fuel Properly Before A Half Marathon Or Marathon

Every engine needs fuel, and your body is no different. No matter how well you've trained, poor nutrition in the days leading up to a race can leave you running on empty long before you reach the finish line. That's why carb loading has become such an important part of marathon and half marathon preparation. Done properly, it helps maximise the amount of energy stored in your muscles, giving you the best possible chance of running strongly throughout your race.

Carb loading is often misunderstood. Some runners think it means eating enormous plates of pasta the night before a marathon, while others avoid it altogether because it sounds too complicated. The reality lies somewhere in between. It's not about eating as much as possible or giving yourself permission to indulge in unhealthy foods. It's about increasing your carbohydrate intake in a controlled way during the final few days before your race while reducing your training load as part of your taper. Get that balance right and you'll arrive on the start line feeling energised rather than sluggish.

What Are Carbohydrates?

Carbohydrates are one of the three main macronutrients your body needs, alongside protein and fat. They are your body's preferred source of energy during exercise, particularly when you're running for longer than an hour or working at a higher intensity. Once eaten, carbohydrates are broken down into glucose and either used immediately for energy or stored as glycogen in your muscles and liver, ready to fuel future exercise.

Carbohydrates are found in a huge variety of foods, including bread, rice, pasta, potatoes, oats, fruit, vegetables, cereals and dairy products. Sports drinks, energy bars and gels also provide carbohydrates and can play an important role during longer races. Rather than thinking about "good" and "bad" carbohydrates, it's more useful to focus on choosing mostly nutritious carbohydrate-rich foods while recognising that faster-digesting options can have a place around training and racing.

Do All Runners Need To Carb Load?

The simple answer is no. If you're running a 5K or 10K, your normal glycogen stores are usually more than enough to fuel the race, provided you've been eating a balanced diet. Carb loading becomes much more beneficial when you're tackling events lasting around 90 minutes or longer, which is why it's most commonly associated with half marathons, marathons and ultra-distance events.

Even then, carb loading is only one part of the bigger picture. It cannot make up for missed training or poor race preparation. Think of it as putting a full tank of fuel into a well-maintained car. If the engine isn't ready, filling the tank won't solve the problem. Good training, sensible pacing and appropriate nutrition all work together to produce your best performance.

How Carb Loading Works

Your muscles naturally store carbohydrate in the form of glycogen, but those stores have a limit. During longer races, particularly marathons, glycogen gradually becomes depleted. Once levels drop too low, runners experience the familiar feeling known as "hitting the wall", where maintaining pace suddenly becomes much more difficult.

Carb loading works by increasing those glycogen stores above their normal levels before race day. Because you'll already be reducing your training during the taper, your body has the opportunity to store more carbohydrate than it would during heavier training weeks. This gives you a larger energy reserve to draw upon during the race, helping delay fatigue and allowing you to maintain your pace for longer.

When Should You Start Carb Loading?

Modern sports nutrition advice has moved away from the complicated week-long loading plans that were once popular. For most recreational runners, increasing carbohydrate intake during the final two to three days before a marathon is perfectly adequate. This approach is simpler, easier to manage and avoids the need for dramatic changes to your normal diet.

Rather than eating huge meals, it's usually better to increase the proportion of carbohydrate on your plate while slightly reducing foods that are higher in fat. Rice, pasta, potatoes, bread, oats, fruit and cereals can all contribute towards your increased carbohydrate intake. Drinking some of your carbohydrates through fruit juice, smoothies or sports drinks can also help if you're struggling to eat larger amounts of food.

Fruit smoothies are a great source of carbohydrates

Practise Before Race Day

Like every other part of your race preparation, carb loading should be practised before an important event. Your longest training weekends provide the ideal opportunity to experiment with different foods and meal timings so that nothing comes as a surprise on race week. Every runner responds slightly differently, and finding an approach that leaves you feeling energised rather than bloated is an important part of the process.

This is also the perfect time to test any sports drinks, energy gels or carbohydrate-rich snacks you intend to use during the race itself. Your stomach adapts to what you regularly consume in training, so introducing unfamiliar products on race day is rarely a good idea.

Race Week Nutrition

The final few days before your race aren't the time to dramatically change your diet. Stick to familiar foods that you know suit your digestive system and avoid the temptation to celebrate with a large takeaway or restaurant meal. Rich, spicy or particularly fatty foods may taste appealing, but they can increase the risk of stomach problems at exactly the wrong time.

Many runners also reduce their fibre intake slightly during the final 24 to 48 hours before a marathon. This isn't because fibre is unhealthy, far from it, but because reducing high-fibre foods can minimise the likelihood of digestive discomfort during the race. White bread, white rice and regular pasta often replace wholegrain alternatives during this short period before normal eating resumes afterwards.

What About Breakfast On Race Morning?

Race morning is not part of carb loading, it's simply your final opportunity to top up your energy stores before the start. Aim to eat breakfast around two to three hours before your race, choosing foods you've already tested during training. Toast with jam, porridge with banana, cereal or a bagel are all popular choices because they provide easily digested carbohydrates without sitting too heavily in the stomach.

Don't forget hydration. Sip fluids steadily during the morning rather than drinking large amounts immediately before the gun goes. If your event provides a sports drink on the course and you've trained with it beforehand, this can also form part of your overall race nutrition strategy.

Common Carb Loading Mistakes

The biggest mistake many runners make is assuming carb loading means eating as much pasta as possible. In reality, it's about increasing your carbohydrate intake while maintaining a balanced diet, not dramatically increasing your total calorie intake. Overeating can leave you feeling sluggish and uncomfortable before you've even reached the start line.

Another common mistake is trying new foods during race week. However tempting that special pre-race meal might seem, now isn't the time to experiment. Stick with foods you've eaten successfully throughout training. Finally, remember that carb loading only works when combined with reduced training. If you continue running hard throughout the final few days, you'll simply burn through the extra glycogen you're trying to store.

Final Thoughts

Carb loading doesn't need to be complicated. If you're preparing for a half marathon or marathon, increasing your carbohydrate intake over the final two or three days before your race can help maximise your energy stores and improve your chances of performing at your best. Combined with sensible pacing, good hydration and a race nutrition plan you've already practised in training, it can make a significant difference when the miles begin to add up.

Perhaps the most important thing to remember is that race day nutrition starts long before the starting gun. Practise your carb loading strategy during training, find the foods that work best for you and resist the temptation to try anything new during race week. Turn up at the start line with a full tank of fuel and you'll give yourself every opportunity to enjoy the race you've worked so hard to prepare for.

CHECK OUT OUR MEMBERSHIP PLANS