Fuelling for a multi-day ultra

Sports scientist Andy Blow on what to take in before, during and after each stage of a gruelling multi-stage event

Coast Ultra Xtreme

by Andy Blow |

It’s been said that ultra marathons are just an eating and drinking competition with some running thrown in. And never do these words ring more true than when you’re tackling a multi-day ultra.

Taking in the right amount of fuel, fluids and electrolytes is – along with a well executed pacing strategy – fundamental to finishing in good shape and enjoying the experience.

What to do before the event

Starting well fuelled

Fuelling starts well in advance of an ultra. Two days out, your priority should be to load up with carbs to maximise stored glycogen in muscles and the liver.

Carb-loading involves tapering training volume whilst increasing carb intake in your diet. Something in the region of 10g of carbs per kg of body weight per day (eg. 700g of carbs per day for a 70kg runner) for two days is around the recommended dose.

This essentially means eating an extra portion of carbs with each main meal, and potentially adding some carb-rich snacks between meals during the final 48 hours before the start. Keeping your diet low in fibre during this phase is also a good idea to help you avoid too much ‘bulk’ in your diet and keep your digestive system clear for the race.

Starting well hydrated

Drinking a little extra water in the final 48 hours is a sensible precaution, but a key pre-hydration routine to follow is drinking around 500ml of a very strong electrolyte drink the night before and again on the morning of the start. The high level of sodium helps your body to absorb and retain some additional fluid.

During the stages

Once the event is under way, a useful mindset to adopt is that you’re not just eating and drinking for today but also for tomorrow’s stage. Tucking in within the first hour and topping up frequently is the best approach.

Carbs per hour

Carbs should form the backbone of what you take in on the move. Recommendations on dose vary from 60-90g per hour (two or three standard energy gels) depending on your pace and, to a lesser extent, your body size.

Using tried and tested sports nutrition products such as energy gels, chews and bars for the bulk of your carb intake is convenient, as you can test these out in training and know exactly what levels of carbs you’re taking in.

Depending on your preference, you’re also likely to supplement your baseline carb intake with additional ‘real foods’ at aid stations. There’s nothing wrong with listening to your body and taking a little bit of what you feel like eating as you pass through these stops.

However, aid station calories are best viewed as additional calories and should not form the core of your fuelling plan – you don’t want to be reliant on the checkpoints for all of your energy and hydration needs.

Staying hydrated

Fluids and electrolytes are clearly also very important, but the amount of these you’ll need is going to vary dramatically based on the climate and your individual rates of sweat and sodium loss.

In cooler conditions and for those who have low sweat rates, as little as 250-300ml of fluid and negligible sodium intake can be enough. But in the heat, athletes with heavy sweat and sodium losses can drink over a litre of water per hour and take in as much as 1500mg of sodium with that.

You can use the free hydration planning tools at precisionhydration.com to give you a ballpark idea of what your fluid and sodium needs are likely to be, then refine your intake with some organised trial and error during long training sessions in the build-up.

After each stage

Immediately after finishing a stage, your number one priority is to kickstart your recovery. You have a limited window between finishing and being back on the startline again the next morning, so rehydrating and replenishing glycogen stores should begin as soon as possible.

A sodium-rich drink and a carb with a protein-based energy bar is one way to start that as soon as you cross the line.

Soon after that, sitting down to a proper meal with large amounts of carbs, some protein and plenty of vegetables and fruit is step two.

Don’t be shy with the salt shaker – it will help replace your sodium losses, especially if it’s been a hot, sweaty day. It’ll also assist with the retention of any fluids you drink with the meal.

Depending on how late in the day you finish, it may be worth adding in another carb and protein rich snack before bedtime to further top up your tanks. You definitely don’t want to go to sleep hungry. Have a bottle of water by your bedside in case you wake up thirsty, and try to get as much sleep as you can to give the body some rest and time to process all of the calories you’ve taken on board.

Whilst it is something of a generalisation, it’s fair to say that vastly more athletes suffer from under-fuelling and, to a lesser extent, under-hydrating during multi-day ultras. As such, being quite ambitious with regards to how much you aim to eat and drink is likely to stand you in better stead than taking an overly conservative approach.

What does it take?

Here’s a fuelling and hydration plan for before, during and after each stage, taken from a colleague of Andy’s who was training for the Asics Coast Ultra Xtreme.


Precision Hydration 1500. An extra-strong electrolyte drink (1500mg sodium per litre) for pre-loading. One tablet in 500ml the night before each stage and another 90mins before the start.


Precision Fuel PF 30 Gel. A neutral tasting energy gel with 30g of carbohydrate per serving and 2:1 glucose:fructose ratio for easy absorption in the gut. One to three per hour depending on individual need (use the quick carb calculator at precisionhydration.com).

Precision Hydration Electrolyte Capsules (swallowed with water from aid stations). Contains 250mg sodium per capsule for simple and accurate replacement of electrolytes lost in sweat.

Clif Bar Shot Bloks. Simple, digestible carbs in chewable format. Carb content varies by flavour.


Precision Hydration 1500. Also useful for rapid rehydration after each stage. One or two bottles (one tablet or packet in 500ml) in the hours immediately after finishing.

Clif Bar Builder’s Bar. Energy bar including 20g of protein to kickstart the recovery process immediately post-stage, before getting a proper meal inside you.

About the author

Andy Blow is a sports scientist and expert in hydration. He was once the team sports scientist for the Benetton and Renault Formula 1 teams and remains an adviser to the Porsche Human Performance Centre at Silverstone. He has raced a number of trail events and owns Precision Hydration__


Thanks to the teams at Precision Hydration and Clif, the Asics Coast Ultra Xtreme team is giving Trail Running readers discounts on their sports nutrition products.

For 15% off Precision Hydration’s range of electrolytes and fuel use code ‘COASTULTRAXTREME’ at precisionhydration.com.

For Clif use code ‘VOTWO20’ to receive 20% off at the checkout at naturalthyme.co.uk.

Main pic: Nutrition is an important aspect of events like this, the Coast Ultra Xtreme (credit: Ryan Sosna-Bowd)

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