How to Fuel a Marathon: Avoid the Wall and Run Your Best Race
Whether you’re training for your first marathon or looking to improve on a previous performance, one thing is clear: a well-practised fuelling and hydration plan is essential if you want to perform at your best and steer clear of common nutrition pitfalls.
Training for a marathon places a high demand on your body’s energy systems. The most common issues runners face include dehydration, running low on fuel, cramping, gut distress, and even overhydration. The good news is, with a little planning and regular practice, most of these problems can be avoided.
Fuelling Your Training Runs
Your long training runs are the ideal time to rehearse your nutrition strategy. Use them to trial different foods, drinks, timings and quantities. Everyone’s gut is different, and what works well for one runner might not suit another, so experiment early and find out what works for you.
Carbohydrates are your primary fuel source during endurance exercise, delivering energy to your muscles quickly and efficiently. However, your body can only store around 500g of carbohydrate as glycogen, enough for approximately 90–120 minutes of running, which means you’ll need to top up during the race to avoid hitting the wall.
Many runners prefer training early in the morning, particularly on weekends. If you’re running long first thing, focus on eating plenty of carbohydrate-rich foods the day before. This will ensure your glycogen stores are well stocked. Eating a pre-run breakfast will help top up liver glycogen stores, which are depleted during the overnight fast, as well as provide fuel for the early part of your run. Focus on carb-rich, low fat foods, such as porridge, overnight oats, bananas, bagels or toast. Avoid too much fibre if your gut is sensitive and prone to symptoms such as cramping, gas or urgency during running.
You can skip a full breakfast if you prefer, but do try to have a small amount of carbs 15–30 minutes beforehand - something like a banana, a slice of toast with honey, or a gel or bar.
If eating solid food feels uncomfortable that early, opt for a liquid source of fuel such as a sports drink, diluted fruit juice or a smoothie. These will provide quick-acting carbohydrates and fluid to help maintain your energy and hydration levels.
Practise Your Strategy
Aim to simulate race-day conditions during at least two or three of your long training runs. Use the same types of fuel, taken at the same intervals and quantities you plan to use on race day. This will help build confidence and minimise surprises on the big day.
Also practise drinking while running as it can take a bit of getting used to. Start with small sips and build up gradually. If you plan to use the drinks provided by the race organisers, check in advance what will be available and practise with them during training.
Start fuelling early - about 30-45 minutes into your long run - and continue at regular intervals (e.g. every 20 - 30 minutes). One of the most common mistakes runners make is underfuelling. This can quickly result in fatigue and increase the risk if hitting the wall. As a general guideline, runners finishing in:
5 - 6 hours: Aim for 30 - 60g carbs/hour
4 - 5 hours: Aim for 50 - 70g carbs/hour
< 4 hours: 60 - 90g carbs/hour (ideally from multiple carb sources like glucose + fructose)
Many runners need more carbohydrate than they think. Some examples of 30g carbohydrate portions include:
1 large banana
500ml isotonic sports drink
1 cereal or fruit + nut bar (check label for carb content)
2 Medjool dates
1 energy gel (check the label for carb content)
4 energy chews
2–3 Days Before the Race: Carb-Load
In the final days before the marathon, you’ll want to arrive at the start line with fully stocked glycogen stores. This is where carbohydrate loading comes in.
Begin reducing your training volume - known as tapering - in the 2–3 weeks leading up to the race. During the final 2–3 days, increase your intake of high-carb foods like pasta, rice, oats, potatoes and sweet potatoes. Shift your plate so that carbs make up a larger portion of your meals, while slightly reducing fat and protein to make room.
Be mindful not to overeat. Carb-loading is about increasing the proportion of carbs in your diet, not the total quantity of food. Eating too much - particularly late in the evening - can lead to bloating, digestive upset and sluggishness. If you’re prone to gut issues, consider lowering your fibre intake in the 48 hours before the race to reduce the risk of symptoms.
The Day Before the Race
Plan your main meal for lunchtime rather than late in the evening. This gives your body plenty of time to digest, so you don’t wake up feeling heavy or bloated. A simple, carb-rich meal with a moderate amount of protein and low fat is ideal. For example:
Pasta with tomato sauce and chicken
Rice with tofu or beans
Jacket potato with hummus or tuna
Avoid trying anything new or unfamiliar - race evening isn’t the time to test a spicy curry or that trendy high-fibre energy bar.
Race Morning
Your pre-race meal should be eaten 2–4 hours before the start to give your body time to digest and absorb nutrients. This meal is all about topping up liver glycogen and helping you start the race well-fuelled.
Stick to familiar, carb-rich foods that you know sit well. Good options include:
Porridge or overnight oats with banana or honey
Granola with yogurt and berries
Toast or bagel with jam or nut butter
Hydration is also key. Aim to drink around 5–10 ml of fluid per kilogram of body weight in the 2–4 hours before the start. Check your urine colour — it should be pale yellow. After that, sip as needed, but avoid overdrinking.
15–30 Minutes Before the Start
If you skipped breakfast or still feel hungry close to the start, taking in a small amount of carbohydrates can help provide an energy boost for the early miles. Aim for 20–30g of carbs with some fluid. Options include:
A banana
A gel
Half an energy bar
A small bottle of sports drink
This is optional - if you don’t feel like it, don’t force it.
During the Race
Follow the fuelling and hydration plan you’ve practised in training. Stick with products you know work for you and avoid trying anything new on the day - even if it’s being handed out on the course. Carry more fuel than you expect to need (in pockets or a belt) to account for accidental drops or higher-than-expected fatigue.
Once the race begins, maintaining carbohydrate availability is key. Running for longer than 90 minutes will gradually deplete glycogen stores, regardless of how well you’ve fuelled beforehand, so topping up regularly helps delay fatigue and reduce the risk of “hitting the wall.”
Begin fuelling early (within the first 30–45 minutes) and continue at regular intervals. Because carbohydrate takes around 15–30 minutes to become available to your muscles, fuelling consistently helps you stay ahead of your needs.
Use a mix of carbohydrate sources you’ve practised in training, such as gels, chews, sports drinks, diluted juice, dried fruit, or small portions of easily digested foods. Some runners prefer more solid foods early on, switching to gels later as intensity increases. If using gels, take them with water to support absorption and reduce the risk of gastrointestinal discomfort.
Be ready to adapt your strategy if conditions change. On a hot day, you may need to drink more; if you start to feel nauseous or bloated, you might need to ease off the carbs for a short period.
Keep in mind:
Aim for 30–90g of carbs per hour, depending on your speed/ finish time.
Hydrate according to thirst and conditions - most runners will fall somewhere between 300–800ml per hour.
Start drinking early and sip regularly rather than trying to “catch up” later.
Drinking too little can increase heart rate and perceived effort, while overdrinking can lead to bloating or, in extreme cases, low blood sodium levels.
Include electrolytes where needed, particularly in warmer conditions or if you’re a heavier or saltier sweater.
What about going above 90g per hour?
You may have seen elite runners pushing carbohydrate intake above 90g per hour. While traditional guidance suggested a maximum of around 90g per hour (using a mix of glucose and fructose), newer research shows that well-trained athletes can tolerate higher intakes, up to around 120g per hour, when properly adapted.
These higher intakes are typically only beneficial for runners working at high intensities with very high energy demands. They also require structured gut training, gradually increasing carbohydrate intake in training to improve tolerance and reduce the risk of gastrointestinal discomfort.
For most marathon runners, focusing on 30–90g per hour is more than sufficient.
Aid Station Strategy
If you don’t have access to personal bottles, it’s usually wise to carry a good proportion of your nutrition in a belt, pockets or sleeves so you can reliably hit your targets.
Check in advance what products are available on course, how much carbohydrate they provide, and whether stations offer water, sports drink, or both.
Work out roughly how often you’ll reach aid stations based on your pace.
Aim for the later tables in each station to avoid congestion, and make eye contact (or point) to the volunteer you’re heading towards.
Don’t be afraid to slow slightly - a few seconds here can save you minutes later. Stay alert, as runners around you may change direction suddenly when reaching for drinks.
Some runners find it helpful to carry a small soft flask or bottle early in the race to stay self-sufficient and avoid busy stations.
Managing Mid-Race GI Issues
Gastrointestinal discomfort is one of the most common reasons runners struggle in a marathon. If symptoms start to build, try to stay calm and focus on what you can adjust in the moment.
Slowing your pace slightly, switching to fluids, spacing out your intake, or taking smaller, more frequent sips can often help symptoms settle. Being flexible and having practised different approaches in training can make a big difference.
After the Race
Recovery starts as soon as you cross the finish line. Begin by rehydrating - water, electrolyte drinks or a recovery formula can all help replace lost fluids.
Next, focus on food. Aim to eat a recovery meal or snack within 60–90 minutes containing both carbohydrate and protein to replenish glycogen and support muscle repair. Include some colourful fruit or vegetables to help reduce inflammation and oxidative stress.
Great post-race options include:
A smoothie made with milk, fruit and protein powder
Yogurt with granola and berries
Rice with chicken and vegetables
A veggie omelette with toast or potatoes
After that? You’ve earned a treat, so enjoy whatever you fancy!
Final Thoughts
Your marathon nutrition plan should be just as personalised as your training programme. Practise early and often, pay attention to how your body responds, and trust your plan on race day.
Key Takeaways:
Carb-load efficiently and taper your training
Practise your fuelling strategy on long runs
Stick to familiar foods and drinks on race day
Hydrate according to thirst and conditions
Refuel with carbs and protein after the race