At its core, carb loading is a strategic approach athletes use to maximise glycogen storage in their muscles and liver before a long endurance event.

Glycogen is a form of glucose that the body stores for energy. During endurance activities, your muscles rely heavily on this glycogen reserve.

When these stores are depleted, you experience fatigue and a significant drop in performance, often called “hitting the wall” or “bonking”.

The purpose of carb loading is to increase the amount of glycogen stored in the body beyond its normal resting levels.

This is achieved by adjusting dietary intake in the days leading up to a major event, ensuring that the body has ample energy reserves to draw from when needed most.

Given all the hubbub around carb loading, what are the benefits?

Enhanced Endurance

Carb loading significantly boosts endurance by maximising the body’s glycogen stores before a long-duration event. Glycogen, the primary muscle fuel during prolonged activity, helps athletes maintain their energy levels for longer periods.

This is crucial for endurance sports like marathons and ultra races, as it prevents early fatigue and allows for consistent performance throughout the event

Improved Performance

Several studies have demonstrated the positive impact of carb loading on athletic performance.

Research has shown that athletes who engage in carb loading before an event can improve their performance compared to those who do not.

For instance, a study in the National Library of Medicine casts doubt on the benefits of carb loading before short events, but states, “elevated starting muscle glycogen content will postpone fatigue by approximately 20% in endurance events lasting more than 90 minutes”.

This is why carb loading is important for marathons or ultra-racing. If you take part in these events or activities, carb loading should be part of your process.

Delay Fatigue

One of the most significant benefits of carb loading is its ability to delay the onset of fatigue. Fatigue during endurance events is often caused by the depletion of muscle glycogen stores.

When these stores are exhausted, the body must rely more on fat as an energy source, which is less efficient and leads to a noticeable decline in performance.

By maintaining higher glycogen levels through carb loading, athletes can delay this transition and sustain optimal performance for extended periods.

This delay in fatigue allows athletes to push harder and maintain their competitive edge, even in the final stages of a race.

Drawbacks of Traditional Carb Loading Methods

While traditional carb-loading methods have been popular for decades, they come with several drawbacks:

Digestive Issues: Consuming large quantities of pasta and other carb-heavy foods can lead to bloating and digestive discomfort, especially problematic on race day.

Timing and Efficiency: Getting the timing right is tricky. Overeating too late can make you sluggish, while eating too early might not maximise glycogen stores effectively, disrupting pre-race routines.

Weight Gain: Loading up on carbs can lead to temporary weight gain due to water retention, which can feel counterproductive to performance goals by adding extra weight that slows you down.

It’s not enough for modern events: Quite simply, even the most effiecient body can’t hold enough stores to keep you going for some of today’s ultra events. Marathons are a struggle, but with people regularly now running Ultra Marathons (any distance over a marathon), multi-day and more you are going to need more than just your glycogen stores for energy.

You’ll be familiar with these methods if you are a long-term carb-loading aficionado.

Pasta Parties

The night before a big race, it’s common to see runners gathering for a pasta party, loading up on hefty plates of spaghetti, believing that it will fuel their muscles for the challenge ahead. These social gatherings have become a pre-race ritual, where athletes bond over pasta bowls, sharing excitement and nervous energy.

This can be a fun way to relax and catch up with friends old and new, especially if you are away from home for a race or event. We recommend some light protein here and have some light fish or chicken. Even better if it’s oily fish, the good fats from something like a sardine and the protein and carbs will help keep you satiated for longer.

Other Foods

Beyond pasta, traditional carb-loading diets often include other high-carb staples like bread, rice, and potatoes. These foods have long been favourites for their ability to pack glycogen into muscles, preparing the body for the upcoming endurance test. Nowadays, you want to consider lower glycemic index options, such as leafy greens, brown rice, and pasta, but finding some butternut squash or sweet potatoes would be even better. These options provide more nutrients and fibre than plain old processed carbs might. That said, it would be great just to eat a stack of pancakes!

Some people struggle with all this eating malarky. There can be a psychological downside to carb loading. After training for months and maybe changing your eating habits, diet, or even lifestyle, the thought of having a big bowl of pasta or chomping down on jacket potatoes before a big race might not be so appealing; it might go against your main thoughts about how best to prepare for an event.

As mentioned above, even with carb-loading, your body’s glycogen stores will only last so long. The common belief is that the average body can hold around 400 to 500 grams of glycogen in its muscles and another 100 in the liver.

If every gram can give you around 4 calories, this will only equate to around 2’000 calories. And if you have ever done a long cycle, you’ll know that won’t get you that far. At an average burn rate of 800 calories per hour, this is about 2.5 hours.

Of course, when your glycogen runs out, your body increases its reliance on fat. Which is more abundant but way less efficient.

Your body oxidises the fat to keep you moving, but you most likely won’t be running or cycling hard, not to mention how you might feel.

Modern endurance fuels are a better fit for today’s athletes. Keeping your glycogen topped up on the way around an ultra-style event is probably the wisest way to complete one.

They eliminate the need to try and deal with your body oxidising fat, feeling terrible when you just want to get on and perform at your best.

The critical requirements are that it can be taken around the course, used on the fly, and be palatable and easily digestible without causing a gut upset.

Every advantage counts when crossing up to 200 miles in a single event. The research findings here demonstrate the benefits of modern carb-loading methods and marry these with a modern endurance fuel that is up to the task.

Resources:

Carbohydrate-loading and exercise performance. An update: https://pubmed.ncbi.nlm.nih.gov/9291549/

A comparative observational study of carbohydrate intake and
continuous blood glucose levels in relation to performance in ultramarathon: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10784534/