What’s the Best Nutrition for the Marathon?

Apr 12, 2021

This information is adapted from the work of Julia Mainstone, a Sports Nutritionist. The following is a guideline only. Please seek professional advice prior to commencing a Marathon.

Nutrition plays a big part in getting the best results from training and achieving your optimum performance. Of course, you can still run if your diet’s not great, but it will feel so much easier if you eat like a professional long-distance runner.

How does the body produce energy to run? 

Here’s the Science bit! Its all down to Energy and Carbohydrate Metabolism. Different sports use different energy systems within the body. A runner like Usain Bolt will use completely different energy pathways to a runner like Mo Farah because as we exercise for longer, the energy systems used change completely. As the distance you run gets longer, more of the energy contribution to the race comes from aerobic metabolism. During a marathon more than 99% of the energy you use will come from breaking down glycogen (type of sugar) stores aerobically, fat burning or oxidation and any additional carbohydrate you take on during the race.

So, the first piece of advice – get those carbohydrates in!

For novice marathon runners, the carbohydrate content of their meals on the day before the event is the most significant predictor of race performance. Carbohydrates often get a bad press, but they are essential for endurance athletes, and probably at higher levels than you may be used to. However, if you’re going to eat a high-carbohydrate diet, try and make as many of the carbohydrates you choose as healthy as possible (oats, brown rice, other wholegrains, sweet potatoes and quinoa). It can be hard to reach the high levels of carbohydrates needed with these healthy starchy carbs, so supplement this with dried fruit, juices and as many natural high-carbohydrate foods as you can. The aim is to keep glycogen levels constantly high and recover quickly between sessions so you can get the most out of your training. Keep this level of carbohydrate intake even when you taper before the event so you can maximise your pre-race glycogen levels.

What happens if I don’t?

Runners not eating a high-carbohydrate diet are more vulnerable to the dreaded upper-respiratory tract infections that often plague endurance athletes. It’s also important to get the carbohydrates in after your event and recover quickly, as this is a period where you will be extra vulnerable to infection. It’s very common to experience loss of appetite after an event or training, but fight it if possible and eat as soon as you can.

Overleaf is a table which you can use to calculate your daily carbohydrate needs. Find the training load that best describes your training, and then calculate your carbohydrate needs using your body mass. On days where you train less, aim for the lower end of the range, and on days you train for longer aim for the higher end of the range. And remember, for example, that 100g rice does not equal 100g carbohydrates, rice is only about 70% carbohydrate, so start looking at nutrition labels and try to calculate if you’re getting the right amount.

Your protein needs are going to stay pretty constant and don’t need to be adapted to your levels of training as much as your carbohydrate intake. Guidelines suggest amounts of around 1.1-1.7g per kilogram of bodyweight a day depending on your goals and whether you undertake strength training on top of your running. As long as you are getting regular doses of protein into your body, especially at breakfast (a time where protein is often neglected) and after training sessions you don’t need to worry about protein too much; the key is small, regular amounts.

Immediately after running, the most important nutrients to get into you are carbohydrates and a small amount of protein. However, if you take care of those straight away, it then becomes important to replace fat stores in muscle, so don’t neglect fat in your diet, especially if you are already very lean.

Sports Products and Fluid Needs

Despite the controversy, there is a place for energy bars, drinks and gels in endurance sports. Studies clearly show runners who take on extra carbohydrates during the race perform better. Taking on food as you run is an acquired skill and needs to be practiced as otherwise you can end up with rather unpleasant gastro-intestinal problems, the last thing you need in an event. This can also be true with bars and gels. We must stress, practice what you are going to do in the race. This includes your clothing, and above all your fluids and the exact gels you are going to use. Your gut needs to be trained too, not just to cope with eating/drinking whilst running but also so you absorb the maximum amount of carbohydrate from the food.

For events or training sessions up to 4 hours, aim to take on 30-60g of carbohydrate an hour. In ultra-endurance events you can train the body to absorb 90g of carbohydrate an hour. This is independent of bodyweight; it’s all down to how well your digestive system has adapted to absorb carbohydrate. You can make your own energy drinks easily enough, but the combinations of sugars used in gels and properly designed sports products have been shown to be most effectively absorbed.


Dehydration completely changes how you feel during a race. Perceived effort is much higher when you start becoming dehydrated, along with extra stress on your cardiovascular system and more risk of gastro-intestinal problems. Whilst everyone sweats at different rates and sweats out different amounts of minerals, a good general guide is that you should aim to lose no more than 2% of your bodyweight as sweat during a training session or event.

ACSM guidelines suggest a possible starting point for marathon runners (who are hydrated at the start) is they drink ad libitum from 0.4 to 0.8 litres per hour, with the higher rates for faster, heavier individuals competing in warm environments and the lower rates for the slower, lighter persons competing in cooler environments.

Take note please: – don’t ever drink more water than you need as it can lead to hypernatremia (low sodium levels) if you are using water alone. Sodium is the mineral you need to be most concerned about losing during exercise, and this is definitely a good reason to consider using sports drinks, as they contain sodium and normally a carbohydrate content of 4-8%.

It’s all about experimenting in training to find out what works best for you. There is no magic pre-event meal which will turn us all into Paula Radcliffe or Mo Farah; the perfect diet and foods for you are personal and individual, although a pre-marathon meal should always be rich in carbohydrate. You can only find the perfect meal for you by experimentation, experience and practice.

Remember it is a great achievement to put the training in to get to Race Day! Enjoy the Day! 

Good luck from all the Team at The JSSC!