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Fuelling a Marathon!!

With just over 4 weeks until the London marathon, we thought it was time to get a 101 on fuelling before, during, and after up on the site! Before we turn our attention to the practical, a little science to set the scene ...

Most of your energy in an endurance event like a marathon will come from your aerobic energy system. The anaerobic systems will also be active, and the relative contribution of this will largely depend how fast you run! The only fuel for the anaerobic system, and the primary fuel for the aerobic system (when available) is carbohydrate in the form of glucose from the blood and glycogen stored in the liver and muscle. Fat will be used by the aerobic system to a greater or lesser degree depending on the availability of carbohydrates, your speed, and how adapted you are to use fats efficiently. But it is the sub-optimal fuel for the fastest marathon you have the capacity for, as it requires more oxygen to release the same amount of energy and takes longer to access that energy.


  • Reduce fibre intake by 25-75%. Switch to “white” bread, rice and pasta and opt for low fibre fruit and veggies, such as peppers, tomatoes, carrots, green beans, melon and peeled apricots and peaches.

  • Increase salt intake (in particular sodium) to maintain your electrolyte balance and support optimal hydration on race day. Consider drinking coconut water, cows milk, water with electrolyte tabs and / or adding an extra pinch of salt to main meals.


Carb load! We want to hit the marathon with our muscles fully loaded with carbohydrate (glycogen) stores.

  • Aim to consume 8-10g/kg bodyweight in carbohydrates per day in those two days, or at least 15% more carbs than we normally eat day to day.

  • If this feels like a lot, ways to increase intake without feeling overstuffed include adding honey or maple syrup to any sweet meals or drinks, having jelly sweets as snacks, and drinking carbohydrate sports drinks (like the ones you are likely to include during the race!).

  • If you are training, particularly HIIT training, get a big carb feed in (1-2g/kg bodyweight) straight after training to maximise the period after training where your body loads carbs in the muscle most effectively.

For every molecule of glycogen stored, you also store 3 molecules of water – so if your weight increases slightly in this period, do not worry. It is a sign you are loading up those stores.


In addition to keeping the carbs high and the fibre low, get a hit of protein so the body is well repaired ahead of the race, and keep fat and spice low to reduce the risk of these in your gut causing distress during the race.

Typical ‘night before’ meals include:

  • Spaghetti Bolognese

  • Pasta with tomato sauce and fat free cottage cheese

  • Chicken or fish and white rice

  • Baked potato and tinned tuna or a little baked beans

  • Pizza, with just a little cheese and lean meats, or some well cooked peppers or courgette

  • Ham sandwiches

All with added salt, and taken with at least a large glass or two of water.



If you have eaten and tapered your training appropriately in the days and weeks leading up to the event, you shouldn’t need to use the morning of race day to seriously fuel. It should serve just to top up your glycogen and blood glucose stores!

  • If you can, 2-4 hours pre race eat a breakfast that – similar to dinner – is low fat and fibre, and high carb.

  • Up to 50% of endurance athletes have reported gastro issues in one or more of their events (nerves plus jostled insides as you move!). If you are susceptible to, or worried about this, consume a liquid meal.

Typical ‘morning of’ meals include:

  • Large bowl of porridge with skimmed milk, egg white, honey and berries

  • Toast topped with high protein low fat yoghurt and jam

  • Large bowl of low fibre cereal and a protein shake

  • Smoothie made with protein powder, oats, honey, ripe banana, milk, and a pinch of salt

Taken with at least a large glass or two of water.

You may also consider caffeine. It is possibly the most popular ergogenic aid amongst athletes at a dose of around 1-6mg/kg bodyweight 30 mins or so before an event. But caffeine sensitivity differs extensively between individuals and so test dosages in advance. If you get jittery, you have probably taken too much!


Carbohydrates!!! When these deplete we “hit the wall”. And assuming we begin a run with full carbohydrate stores, we are expected to deplete our stores within 60-90 minutes or so of a moderate paced run and sooner if you’re running faster.

So we need to consume carbohydrates during the run to maintain our pace. As well as hydrate to digest and absorb the carbs effectively, as well as to keep our body functioning. For a marathon, we aim to take on board 60-90g carbs per hour. And to consume 500-750ml electrolyte containing fluid per hour. Spread as evenly as possible through the race for maximal absorption and utilization.

Taking carbs, water and salt on board obviously requires digesting them! And this is where we can come unstuck. Running disrupts the gut and so can make digestion difficult. Resulting in us feeling unwell when we consume things. This issue is made worse if we are already dehydrated, as this also causes gut damage (with or without running).

Luckily, the gut can be trained. Just like with our muscles for running and strength work, we essentially follow a ‘progressive overload’ programme, i.e. gradually increasing the amount of carbohydrate, water and salts we are consuming, in order to build our tolerance. If you have not done this already, start now!!

Typical carbs to take on board:

  • Carbohydrate and electrolyte powders added to water (60-80g carbs per litre)

  • Carbohydrate gels and chews (drink electrolyte containing fluids alongside to aid digestion)

  • … and / or plain old jelly sweets!

Not all carb powders, gels and chews are created equal!! All are based around glucose and fructose, but in different ratios and different types of glucose structures. Some of the gentlest on the gut are those containing maltodextrin or cyclodextrin as the glucose source. Test different products and find what works for you.


When the event is over, appropriate fuelling isn’t!! You need to ensure you refuel to replenish your muscle and liver energy stores, give your muscles the protein they need for repair, and your body the micronutrients it needs so you aren’t hobbling for a week after and requiring daily 3 hr naps!!

Within 15-60 minutes of completing the event, aim to consume 1g/kg bodyweight in carbs, and 0.2-0.4g/kg bodyweight in protein. An easy thing to have straight after the finish line is a whey protein, oat or cows milk, and honey shake as you may not feel like solids and this hits the start of rehydration too (has water and salts!).

Then follow this with a meal rich in at least a big handful protein, as many complex carbs as you fancy and some fats. In all seriousness – a burger, chunky chips (reducing the fat:carb ratio) and a side of salad is a great refuel!!

After that first meal, ensure you continue to eat balanced micronutrient rich meals of complex carbohydrates, protein and fats regularly across the next 48 hours to support your body’s repair and recovery. If you tapered your fibre intake in the days leading up to the event, reintroduce it just as slowly to avoid gastro pain and upset, particularly as your body is already sensitive after the stress of the competition … start with cooked veggies and soft fruits before moving onto the raw hard stuff!


Appropriate nutrition and hydration is VITAL to enabling you to perform to your best in marathons. Get it wrong and your performance will be impacted. The key is to take in enough to fuel you and not too much to slow you down, or worse. It is a fine tightrope!! Every body is different, meaning it is vital you practice your race day nutrition in your training sessions to figure out what works best for you – take the general principles outlined here and in the further reading referenced below, and tweak it until you have something that sees you moving faster than ever to smash those PBs come marathon day!!

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