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How to fuel for a successful London Marathon

How to fuel for a successful London Marathon (part 1)


With just under 30 days to go until the big day, you should use the next few weeks to develop and practice your nutrition strategy to get you around the course.


Fueling the body is a bit like putting fuel in your car. If you add the wrong type of fuel or worse, no fuel at all, then your performance will be severely affected.


So why is nutrition so important for marathon performance?

A high quality, nutritious diet is just 1% of a runner’s development, yet it is the 1% that has an impact on the other 99%. When planned well, nutrition has been shown to have a number of benefits including:

1.   Maximise performance on race day; helping you to hit your target time or even a PB!

2.   Recover effectively; helping you to reduce muscle soreness and fatigue ready for your next long training run and keeping your legs fresh for race day.

3.   Enhance training adaptation; marathon training places huge demands on the body and nutrition can help to further enhance adaptations – helping you to run faster for longer.

4.   Reduce the risk of injury and illness.


Over the next few weeks, the purpose of the upcoming blogs is to help support you with your race day nutrition to ensure you get over the finish line, starting with fueling.


With a few long runs left before the big event. It is vital to practice your race day strategy. I have worked with numerous runners who for previous events, changed what they ate and drank on race day compared to what they had trained with and as a result they suffered with a stitch or gastrointestinal distress (GI) (upset stomach) and ruined their chance of a PB.

So, what should you eat before the race?

Carbohydrate is the main source of fuel for the body during exercise, however we only have limited stores; enough for around 2 hours of high intensity exercise. Therefore, you need to make sure you start your run with energy stores at optimal levels.


Fueling starts 2 to 3 days before the marathon itself right up to the morning of the race. For this article I will focus on fueling during the 24 hours before race start. You can practice this strategy during your long runs.


Race Day – 1 (RD-1)

This is the day before your long run or the race itself. The purpose of this day is to load the muscle with fuel ready for the run the next day.  


This can be done by consuming high carbohydrate meals and snacks throughout the day e.g. Breakfast, mid morning snack, lunch, mid afternoon snack, dinner, pre bed snack.


Example carbohydrate-based foods include:


·      Rice

·      Pasta

·      Bread

·      Potatoes

·      Cereals and porridge


Carb based snacks include:

·      Cereal bars

·      Fruit (dried as well as fresh) and fruit juices



An example run day – 1 (RD-1) nutrition strategy may look something like this:


Race Day (RD)

As you will start running the London Marathon at any time from 9am to 11am (depending on your expected finish time) I would recommend starting your long runs at a similar time so that you get used to running and eating around that time.


Fueling for a marathon or long run starts around 3 hours before the start. As the time before the start of the race or run decreases so should the amount of food you consume. Having a high carbohydrate-based meal around this time allows time for the food to digest without increasing the risk of a stitch or you feeling sick.

Keep your pre run meal high in carbohydrate but low in fibre and fat as they take longer to digest and may increase the risk of GI distress.


High carbohydrate snacks such as cereal bars, sports drinks and fruit in the 60 to 90 mins before race start help keep fuel stores topped up.


An example race day nutrition strategy may look something like this.


Is there any supplements that may help with the run?

It is just as important to practice using any sport supplements during training too. There are 100s of supplements currently available for purchase. There are 3 that I would recommend to use:


1.   Caffeine

This is one of the only supplements with strong evidence to show benefits on exercise performance. It is found in a range of foods such as coffee, cola energy drinks (beware of the sugar content) and chocolate. Caffeine acts on central nervous                                    system, it promotes improved reaction time, concentration                                            and reduction in fatigue perception. Current recommendations are to consume 3 to 6 mg per kg body mass 60 minutes before exercise. For a 70kg this would be 210mg, this is a similar content to a double espresso



2.   Dietary Nitrate in the form of concentrated beetroot juice: Nitrate is found in a range of leafy green veg such as spinach, kale, rocket and beetroot. A key effect of dietary nitrate is that it reduces the oxygen demand of exercise, meaning the muscles need less oxygen to maintain a given work rate, thereby improving exercise efficiency, fatigue resistance and exercise performance – perfect for those PB chasers!. Nitrate consumption has been shown to result in a 1 to 3% improvement in time trial performance (IOC supplement statement, 2018). The optimal dose is 400-800mg nitrate for                                 3 to 6 days before an event then a final dose 2 to 3 hours before race start.



3.   Vitamin D. This is Involved in a range of processes in the body. Lack of Vitamin D significantly impacts:

Bone Health (increased risk of fractures)

Muscle function (impairs muscle function and recovery)

Immune health (increased risk of coughs and colds)


Vitamin D comes from the sun however during winter this becomes harder due to lack of daylight hours and poor weather. Certain foods such as oily fish, fortified breakfast cereals and red meats contain small but insufficient amounts of Vit D.


My pre-race nutrition tips:

1.   Use the next few weeks to practice with different meals and quantities to help you work out what’s best. Every runner’s nutrition strategy is different, some foods work better for some than others so please focus on your nutrition rather than copying others.

2.   PRACTICE YOUR RACE STRATEGY AS MUCH AS POSSIBLE – during high intensity exercise such as running, runners are susceptible to ‘runners’ gut’ due to the physical movement of the stomach and intestines, physiological strain due to a reduction in blood flow to the intestine as well as nutritional factors such as hydration, fat and protein. I will talk more about ‘runners’ gut’ in another blog coming up.




In the next blog I shall discuss the nutrition during the race itself or the rest of your long runs. 



About James

James is a Sport and Exercise Nutritionist. He has an MSc in Sport Nutrition from Loughborough University and a BSc in Sport Science from Loughborough University. He is listed on the Sport and Exercise Nutrition register (SENr) too. James works with a range of athletes across a range of ages including rugby, football, golf as well as lots of runners too. You can find out more about James and what he does via his website and you can follow him on Instagram and Facebook: JamesFlemingNutrition or get in touch: .

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