Marathon training nutrition

Marathon training nutrition

We’re well into the swing of spring marathon training. Getting the miles in and staying injury-free are two important parts of the puzzle, but your nutrition is just as key. Here we look the basics of how to fuel your body when marathon training.

Key part of training

Running a marathon is, for many people, one of the more physically demanding endeavours they’ll undertake. Hours spent pounding the streets, hitting the trails or enduring the treadmill, all with the aim of taking on the legendary distance of 26.2 miles.

The estimated calorie expenditure of running is around 100kcal per mile (this is very much an estimate, and will vary depending on lots of individual factors). 26.2 miles would therefore equate to a rough estimate of 2,600 calories. This is only a rough estimate; body weight, sex, age and fitness all have a bearing on how many calories you’ll actually expend, but it’s fair to say that running a marathon carries a pretty hefty energy demand.

So, you’ve entered your race, you have your training plan and you’re putting in the miles. All is in hand, right? Just as important as the long runs, the speed sessions and the rest days, is planning and training for how you are going to fuel your race. Get the fuelling wrong, and you’re not likely to achieve your best, or worse, you could scupper everything by bonking or bringing on a bad case of runner’s gut.

How are you going to fuel your marathon? Let’s have a look at some of the basics of human energy systems. For race day, as with all activity, the energy supplies that keep us going come from several sources: your own body stores (endogenous energy), what you eat and what you drink (exogenous energy).

Body stores

Energy can be drawn from our own body by breaking down stores of fat, protein and glycogen (stored carbohydrate), and these different fuel sources are working in parallel with each other to keep us going, contributing to different degrees depending on the activity and on our diet.


Breaking down protein is a natural part of the fuelling process, to a small degree, but you want to limit it – protein is stored as muscle. And where athletic performance is concerned, breaking down muscle isn’t to be encouraged. This process can be limited by avoiding excessively large calorie deficits, and eating a balanced diet containing carbs, protein and fat.


Fat is a good fuel source, and is particularly useful for endurance sport where the lower intensity/longer duration enables the body to use it more effectively. While some of us store more fat than others, even racing snakes will store thousands upon thousands of calories worth of fat, and that fat is used to partly fuel endurance sports such as marathon running. This is the case for everyone, regardless of what they eat.

Relying on fat alone does not tend to support peak performance due to reduced efficiency (more oxygen is needed), but does decrease reliance on taking in fuel and the difficulties that can entail – fat-reliant athletes can rely on their fat reserves rather than having to take gels, drinks and the like mid-race.

Should you ditch the carbs? That’s up to you. Quite frankly, there’s a lot to it! Do your research (look for reliable sources rather than Dr. Google, and don’t rely on reports of personal experiences; everyone is different and – I’m bracing myself as I write this – some people can be a bit evangelical in their beliefs when it comes to low-carb diets) and weigh up the pros and cons. This is the subject of contentious debate.

To see the benefits your day-to-day diet needs to be low-carb, and for most people that represents a significant change in what they eat and their day-to-day energy levels. The transition to a low-carb diet can be tough (common complaints of tiredness, low energy and reduced concentration are not uncommon), and it takes time to adjust – just how long it takes seems to vary from person to person, and from study to study. On a low-carb diet you might find it difficult to push the intensity of your running effort, and if you like to do a mix of training including high-intensity efforts, then low-carb isn’t necessarily your best option. Fat just doesn’t cut it for short, hard efforts. For such occasions, and for race day itself, strategic use of carbs is recommended to enable you to perform at your best.

If you’ve done your research and you’re up for cutting the carbs, try to maintain a broad nutrient intake (fibre in particular can be an issue) and give thought to the quality of the fats that you’re eating. During training and racing it isn’t strictly necessary to take on anything other than water and electrolytes, as you’ll have ample stores of energy in your own body fat. You might want to eat for reasons of hunger, and that decision is made on an individual basis. And that’s one of the huge benefits of reducing reliance on carbs – you don’t have to worry about sticky gels and sickly sweet drinks that can bring on stomach cramps and wreck a race. As mentioned earlier however, even fat-adapted athletes are advised to use carbs strategically – there’s a time and place for them, and a marathon is one of them.


Our body stores carbohydrates in the form of glycogen, which is stored in the muscles and the liver, but its capacity to do so is limited to enough calories for roughly 90-120 minutes of exercise. Our muscles like glycogen (so does the brain), and perform well when using it as an energy source. However, as the supply is limited, the longer you run the less available it becomes. Eventually, when supplies run low, The Wall looms. With both the muscles and brain running on fumes, the body and mind can feel sluggish and incapable of continuing. The Wall is dreaded by marathon runners, and has sunk many a race.

As the body can’t store enough glycogen to keep you going for the duration of a marathon, it’s necessary to take on more fuel to keep your levels topped up and stop your energy levels from dipping. This is where energy gels, jelly babies, sports drinks and other sugary ergogenic aids come in.

Food and drink

The old adage of you are what you eat might be a cliché, but it’s also true. What fuel is available to power you through marathon training and a marathon is very much linked to what you put into your body. As outlined above, protein, fat and carbohydrates are all used to some degree, and you can influence this based on what you eat and, importantly, when you eat (or drink) it.

There are three key opportunities for fuelling sporting activity: before, during and after.

Fuelling before activity is analogous to starting out on a car journey with a full tank of petrol. While you might be able to get to your destination on half a tank, do you want to risk it? You don’t have to eat mountains of food, but a high-carb, moderate protein, low-fat meal in the 3-4hrs before a marathon can help top up glycogen stores that have been depleted by the night-time fast (assuming, of course, that it’s a morning race) and get you to the starting line with fully stocked muscle glycogen stores.

Fuelling during activity very much requires trial and error. Find an energy source that works for you, that you can stomach and (hopefully) enjoy, and incorporate it into your training runs. NEVER TRY ANYTHING NEW ON RACE DAY! Shouty text intentional – if you’ve not tried it, you can’t trust it. Blood is diverted away from the gut during exercise, and foods/drinks that you can happily digest on a rest day can become indigestible stomach destroyers mid-marathon. Whether it’s a jam sandwich, jelly beans, gels or sports drinks, practise eating and drinking during your longer runs, and stick with what you can tolerate. The general recommendations are 30-60g of carbs per hour, along with fluids and electrolytes.

Fuelling after activity is an opportunity to replenish your body stores, nourish and repair your aching muscles, and support your recovery. Carbs and protein in a 2:1 ratio is recommended, ideally within 30-60 minutes of finishing your race. Add in some fluids and electrolytes to rehydrate, and you’ve got all bases covered.

That’s the basics. Find out more about how you can use food as fuel for running here: