Training for a marathon takes months of discipline, commitment, and physical effort, yet many runners may sabotage their race without even realising it, despite all of the preparation in the lead-up. The most common mistakes aren't always related to fitness, however, as they are often linked to poor decision-making around hydration, pre-marathon nutrition, and race day fueling.

As a marathon places huge demands on the body, if you do not fuel correctly before, during, and after the race, even the strongest training plans can unravel as you clock in the miles. That is why Veloforte has broken down all of the biggest marathon mistakes to avoid, especially those connected to nutrition, as this can make all the difference between a painful struggle to the line and a confident finish. 

One marathon mistake that many runners may fall victim to is underestimating just how important nutrition really is. Some runners may tend to focus almost entirely on long runs and their pace, assuming that their fitness alone will carry them through the 26.2 miles. Unfortunately, this is rarely the case, as pre-marathon nutrition is the foundation of performance. 

Your body relies heavily on carbohydrates for endurance running, and if glycogen stores aren’t properly topped up, fatigue will set in early. Underfueling during training leads to poor recovery and increased risk of energy too, not just low energy levels. 

Therefore, a solid approach to pre-marathon nutrition should start weeks before race day. This means consistently eating enough carbohydrates, balancing protein for muscle repair, and ensuring that your overall calorie intake matches the demands of your training. This is essential as nutrition isn't something you can tweak or fix the night before a marathon, with it being a long, ongoing process to prioritise.

Another common mistake to avoid when running a marathon is skipping fuel during the race. Although you may initially feel fine early on, this can be dangerous, as by the time fatigue sets in, it is often too late to recover fully. During a marathon, glycogen stores will eventually deplete, and after that, your body desperately needs additional fuel. 

Skipping supplements such as energy bars, chews, and smart drinks almost guarantees a drop off in performance during the race's final stages, but a proper fueling strategy can help prevent this. Not waiting for hunger or exhaustion as a signal is also key, as fueling early and consistently maintains your blood sugar levels and reduces the risk of hitting a wall

One of the most avoidable marathon mistakes is trying new foods, drinks, or energy supplements on the day of the race. This is not the time to experiment, and even if something works great for another runner, it may not suit your digestive system. New energy gels, unfamiliar drinks, or even a different breakfast can lead to cramps, bloating, or even nausea, all of which can completely ruin a marathon. Your pre-marathon nutrition strategy should be fully tested during training, and if it hasn't worked, then it does not belong in your race day plan.

Hydration is often overlooked by many, yet it plays a crucial role in marathon performance. Drinking too little can lead to dehydration, dizziness, and cramping, whilst drinking too much without electrolytes can dilute your sodium levels. Sweat loss varies greatly between runners; therefore, hydration needs are individual. It is for these reasons that practising proper hydration alongside your pre-marathon nutrition during training is essential. 

What’s more, relying solely on water during a marathon can also be a costly mistake. Electrolytes help your body absorb fluids and maintain muscle function. As a result, to keep hydration levels balanced through a race, electrolyte powders and premixed drinks are extremely helpful.

Another aspect of marathon preparation that can be poorly executed is carb loading, with many runners either ignoring it completely or overdoing it the night before the race. Effective carb loading is a key part of pre-marathon nutrition and should be done over the final 2-3 days before the race. During this time, training volume decreases while the intake of carbohydrates increases, allowing muscles to store maximum glycogen. 

Good carb loading includes foods such as rice, pasta, potatoes, overnight oats, and low-fibre fruits, as opposed to high-carb junk foods that many runners may resort to. This is to prevent bloating, discomfort, or sluggishness, helping ensure your body is fully fuelled and ready to handle the demands of the upcoming 26.2 miles.

Crossing the finish line doesn't mean your job is done, either, as forgetting post-race recovery is another major mistake that can prolong soreness. After a marathon, your body is depleted and carries muscle damage. Therefore, taking protein bars or powders to repair these is key, and supplementing your body with additional carbohydrates and fluids restores your body's blood sugar and hydration levels. While this technically comes after the race, it is still connected to pre-marathon nutrition because planning it in advance ensures you are ready to refuel immediately after finishing.