Q: Do I need to eat during a marathon?

A: Perhaps not, but you’ll probably be better off doing so.

In this brief guide to how to fuel long runs and races, we’ll give an overview of what is going on in your body and advice on how you might ‘optimise your nutrition strategy’ (or, ‘decide what to eat’ in normal English).

Please note, this is a massive, complex subject that we’ll aim to reduce to just a few hundred words. We will try to keep things simple, which will involve a few generalisations.

However, as with a lot of things that involve running or the body, there is more than one way of doing things. There will always be outliers or exceptions to the norm. Even though we won’t cover everything in full detail here, it should be enough information to get you going and help you decide the approach that works best for you.

Let’s begin…

How much energy does a marathon use?

To start with, we need to understand what is going on in our bodies when we run a long way.

Every step we take requires fuel. We need oxygen, plus a mixture of carbohydrates and fat (and next to no protein, except in certain scenarios). Calories is the unit of measurement used to quantify how much energy is used, or how much energy we can get from a particular food source.

The amount of calories we use is related to how hard we’re running and how long we’re running for, how efficient we are, and how big we are. In general:

  • A long run will use more energy than a short run;
  • A fast run will use more energy than a slow run;
  • A smooth, efficient runner will use less energy than an inefficient runner;
  • A smaller runner will use less energy than a bigger runner.

The exact amounts will vary, but here are four hypothetical runners as examples, all running a marathon on a flat course.


Weighs 50kg and is aiming for a time of 6 hours. At just under 14 mins per mile, he’ll burn about 225 calories an hour, for a total of 1,350 calories.


Weighs 50kg and is aiming for a time of 3 hours. At just under 7 mins per mile, she’ll burn about 710 calories an hour, for a total of 2,130 calories.


Weighs 100kg and is aiming for a time of 6 hours. At just under 14 mins per mile, she’ll burn about 450 calories an hour, for a total of 2,700 calories.


Weighs 100kg and is aiming for a time of 3 hours. At just under 7 mins per mile, he’ll burn about 1,450 calories an hour, for a total of 4,350 calories.

Hopefully these examples demonstrate that each runner could have very different energy needs and what works for one might not work for another. This possibly explains why answers to the question of what Lonely Goat Running Club members eat in a marathon can vary so widely!

How do I get enough energy during a marathon?

If you’re looking at the examples above and thinking How on earth am I supposed to eat so many calories when running?, don’t panic!

You will already have a lot of energy stored in your body, so you just need to top up as you go. To work out how much you need to top up, read on…

What’s the difference between fat and carbs?

As mentioned above, running is usually powered by fat and carbohydrates from food we eat. The carbohydrates could be starchy carbs (from pasta, rice, bread, etc.) or sugary carbs (from sweets, fruit, energy gels, etc.), and are then converted into glycogen (the form of sugar our muscles use). Fat and glycogen work in slightly different ways:

  • Fat is a slow burn energy source. You don’t get a lot of ‘oomph’ from fat, but it lasts a long time. Therefore, it’s great for low intensity exercise, such as walking or running at an easy effort level.
  • Glycogen is a fast burn energy source. It’s powerful, but doesn’t last long. This makes it good for high intensity exercise, such as harder running.

Because fat and glycogen ‘burn’ differently, the body adjusts the ratios we use depending on what we’re doing. At 50% of max effort, the mix is about 50:50. But when running flat out, very little of our energy comes from fat, with glycogen the preferred fuel source.

If we run low on glycogen, it becomes very difficult to maintain a high intensity and it is likely we’ll slow down significantly. This subsequent drop off in performance is what is often referred to as ‘bonking’ or ‘hitting the wall’.

The energy stored in our bodies

As fat is so essential to maintaining so many of our bodily functions, we store it all over our bodies. And because it is such a good slow burn fuel source, a little of it goes a long way. It is almost impossible to run out of fat during exercise.

Glycogen stores, however, are limited. We only store it in our muscles and liver and can get through it relatively quickly. It can only be used by the muscles it is stored in, so we can’t top up our legs with glycogen from our arms, for instance.

On a moderate diet, we might have 1,000 calories worth of glycogen available for lower body exercise. With a high-carb diet, we can boost that up to about 2,000 calories worth, which is why ‘carbo-loading’ in the few days before a marathon is so beneficial.

What does this mean?

We’ve thrown a lot of numbers at you, but hopefully they demonstrate that there are circumstances in which you might not need to eat very much at all (or perhaps nothing) during a marathon.

A runner who has eaten enough carbs in the days before the race, and who is running at a very easy effort level, might get by on a fairly even mixture of stored fat and stored glycogen. Using the examples above, Andy could probably manage it. He will use about 1,350 calories and almost certainly will have more than enough already stored in his body as fat and glycogen, provided he has a decent breakfast.

As soon as you start to increase the effort levels, if you’re chasing a hard PB for example, then you’re going to start burning through your stored glycogen. Duane, in particular, is definitely going to need to top up his glycogen levels when running: He needs 4,350 calories, but is probably only going to get 2,000-3,000 calories from the fat and glycogen stored in his body.

These are just two examples. The exact amount of extra glycogen needed during a marathon varies so much that it would require a much bigger article than this to cover all options (runner size, efficiency, effort level, speed, etc.). Suffice it to say, that looking at the examples given above can give you a rough guideline of how much to aim for, even if you fall somewhere between the four different options. As you can see, most runners are going to need to eat something during a marathon in order to run their best.

What can I eat to top up my glycogen levels when running?

Almost any high carb food is going to help top up your glycogen levels, but some are going to be easier to eat than others!

For example, maltloaf contains a lot of carbs relative to its size, but is so chewy it’ll be difficult to eat when running quickly. Jam is pretty much all sugar, and easy to eat, but isn’t something you can carry easily in your pocket.

A spicy, well-flavoured food might be something you can look forward to eating when the going gets tough, but may prove a little tricky to digest on the move. Whereas a bland food might be easily digested, but unlikely to offer a mood boost after a few hours of running.

Grab and go!

Given the above, lots of runners use energy gels, which have been specifically designed for running and other sports. The benefits are:

  • High sugar content for a decent energy boost;
  • Semi-liquid so easy to digest;
  • Usually nicely flavoured so enjoyable to eat;
  • Widely available in most sports shops or supermarkets;
  • Convenient to carry.

That said, they’re not to everyone’s tastes. They can be sticky, not everyone likes the flavours, and some find the high-sugar content causes issues with their innards. Popular alternative options are:

  • Fresh medjool dates (the fat, juicy ones) – for extra sugar, pop a blob of jam inside after removing the stone;
  • Energy chews or bars, or sweets such as jelly babies – a bit like a gel, but more solid;
  • Sports drinks – a good option if you only need a little top up, as they’re not very calorie dense;
  • Kendal mint cake – old school adventure food;
  • Savoury options – cooked new potatoes, sushi rice balls, or even cold pizza!

The options are almost endless, but if devising your own marathon menu, consider the following:

  • Wet is quick and easy to digest, but dry may be more energy dense;
  • Bland is ‘safer’, but may be unappealing;
  • Little and often (eg. a mouth full every 5km) is going to give a more even energy boost than fewer, bigger meals;
  • To avoid weighing yourself down, opt for something lightweight to carry;
  • And make life easy for yourself by choosing something that doesn’t require much unwrapping when you’re trying to run.

Practice, practice, practice

A recurring theme in the article is that every runner is different, with different energy needs, and different preferences on what to eat. Don’t be afraid to experiment to find what works for you, but please make sure you do your experimenting in training, rather than trying something new for the first time on race day.

Use your short runs to see if you get on with a particular food as you’ll be closer to home if it proves to be a disaster! Then, use your long runs to work out how much of that thing you can eat, or how much you need to avoid bonking and running out of energy. You might even discover that you prefer a mixture of things.

In summary

  • Your body will have a lot of energy already stored, so you may just need to top up that energy;
  • Every runner has different energy needs, so the amount you need to top up will vary;
  • There are lots of different things you could eat when running, so make sure you practice different options in training;
  • Make use of the Lonely Goat Running Club Facebook Chat Group to find out what works for your fellow Goats.


Sources: Much of the information on calorie requirements makes use of the calculations and data cited in pages 4 to 15 of ‘Feed Zone Portables’, by Biju Thomas & Allen Lim, Velopress, 2013.


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