With the London Marathon approaching, thousands of runners will be fine-tuning their training, pacing strategies - and crucially - their nutrition. One of the most talked-about approaches in the final days before race day is carbohydrate loading. But while it’s widely discussed, it’s often misunderstood.
At its core, carbohydrate loading is about maximising the body’s glycogen stores. Glycogen is the stored form of carbohydrate in our muscles and liver, and it acts as the primary fuel source during endurance exercise. When runners “hit the wall” in a marathon, it’s often because these glycogen stores have been depleted.
The goal of carbohydrate loading, therefore, is simple: start the race with as much available energy as possible.
What actually works?
The evidence-based approach to carbohydrate loading is not about eating excessive amounts of pasta the night before the race. Instead, it involves a structured increase in carbohydrate intake over the final 48–72 hours before race day, alongside a reduction in training volume.
During this period, runners should aim for approximately 8–12 grams of carbohydrate per kilogram of body weight per day, depending on their experience and training intensity. This allows muscles to store significantly more glycogen than under normal conditions.
Importantly, this isn’t a last-minute fix. It works best when combined with a well-practised nutrition strategy that has been tested during training.
Common mistakes amateur runners make
One of the biggest misconceptions is that more is always better. Overeating - especially unfamiliar or high-fibre foods - can lead to gastrointestinal discomfort, which is the last thing any runner wants on race day.
Another common issue is leaving it too late. A single high-carbohydrate meal the evening before the marathon will not fully replenish glycogen stores. Effective carbohydrate loading is a short-term strategy, but it still requires planning.
Hydration is also often overlooked. Glycogen storage is linked with water retention, so increasing carbohydrate intake without adequate fluid can limit its effectiveness.
Not all carbs are created equal
In the final days before a marathon, runners should prioritise easily digestible carbohydrate sources - such as rice, pasta, potatoes, and white bread - while reducing very high-fibre foods that can cause digestive issues.
This is not the time to experiment with new foods or follow trends seen on social media. Consistency and familiarity are key.
Fuelling beyond the start line
Carbohydrate loading sets the foundation, but it’s only part of the picture. During the marathon itself, runners still need to consume carbohydrates - typically through gels or sports drinks - to maintain blood glucose levels and delay fatigue.
This is where many amateur runners fall short: they prepare well beforehand but neglect in-race fuelling.
A strategy, not a shortcut
Carbohydrate loading is a scientifically supported strategy that can improve endurance performance - but only when done correctly. It’s not about indulgence or last-minute changes, but about careful planning, practice, and understanding how your body responds.
For those taking on the London Marathon, the message is clear: your nutrition strategy should be as well-rehearsed as your training plan. Done right, it could be the difference between simply finishing and performing at your best.