Fuelling for a marathon: A runner’s guide to getting it right

If you’re one of the many people preparing to tackle 26.2 miles this spring, whether that’s at the London Marathon best hydration packs and vests for training maximal heart rate, you’ve experimented with different energy sources – like gels, chews, sports drinks or even real food – to find out what works for you. You should have trialled various pre-run breakfast options, too, and considered which carbohydrate-rich foods you’ll eat in the days before.

But wait – you haven’t tested any race-related nutrition. So what should you do? Thankfully, you still have some time to explore your options and figure it all out.

To have a safe and successful marathon, you also need to keep on top of your hydration levels, how many gels you’ll likely need to consume during your marathon to keep your energy levels in check all the way to the finish line. You should also start to consider your hydration strategy and understand the amount of water and electrolytes that you’ll need to drink before, during and after your race.

While this might all sound like a lot to think about, especially if you thought that marathons were just about running, fear not – our guide is here to put your fuelling worries at ease.

What – and how much – you eat and drink before and during a marathon can make or break your race.

Fail to fuel properly and you’ll find yourself Runner’s World UK – a point of complete physical exhaustion, where your body runs out of energy – in the final few miles. Meanwhile, if you fail to drink enough water or take on enough electrolytes, you may find yourself experiencing symptoms like gastric distress, nausea and dizziness due to dehydration – which also puts your health at risk.

However, if you’re diligent in devising and executing a good nutrition and hydration plan, you’ll have a positive running experience for the full 26.2 miles.

Carbohydrate is the body’s preferred source of fuel during exercise. It’s broken down into glucose and stored as glycogen in the liver and muscles, then used by the body to provide energy. ‘It takes around 500g of carbohydrate to fill your glycogen stores and, at most, this will last you for 60-90 minutes of running at 55-75% of your maximal heart rate,’ explains sports dietitian Renee McGregor. ‘The faster you go, the sooner your stores will deplete.’

McGregor recommends consuming 30-60g of carbohydrate per hour for the first three hours of your marathon, then increasing this to 60-90g of carbohydrate per hour after that.

Great sources of carbohydrate that can be consumed on the go are sports nutrition products, like energy drinks, gels and bars, as well as bananas and Jelly Babies. According to McGregor, it’s better to consume gels over the space of four or five minutes rather than all in one go, as this slower approach aids absorption.

If you want to ensure that you’re getting enough, first check the packaging of your chosen product to find out how many grams of carbohydrate it contains. Then, you can work out how much of that product you’ll need to take per hour of your marathon to hit that 30-60g goal.

‘Start taking on nutrition in the first 30 minutes of your run, then take on more every 30-40 minutes after that,’ advises McGregor. The atmosphere of big races like the London Marathon can be wonderfully distracting, so if you need reminders to take your mid-run nutrition, set an alert to go off on your running watch, if you can, or make a note on your hand.

Different gels contain varying amounts of carbohydrate, so, again, check the packaging to find out how many you’ll need for your race. If your gel of choice contains 23g of carbohydrate, for example, and you follow the consumption strategy outlined above, you would take six gels over a four-hour marathon to reach a carbohydrate quota of 34.5g of carbohydrate per hour (which gives you 136g of carbohydrate in total).

Most importantly, practise your marathon nutrition strategy during your training, experiment with different products to find your best fit and don't try anything new on race day!

To have a safe and successful marathon, you also need to keep on top of your hydration levels.

‘Along with maintaining hydration, fluid intake during endurance running helps to regulate body temperature (thermoregulation) and ensure adequate plasma (blood) volume,’ says McGregor. ‘When core body temperature rises owing to dehydration, plasma volume decreases, resulting in an increased heart rate, which accelerates fatigue.’

reasons to eat more mackerel Alongside feelings of fatigue and exhaustion, other to look out for include a dry mouth, dark yellow urine, decreased urination, muscle cramping and headaches.

It’s worth noting that your water requirements during a marathon will depend upon personal factors such as your sweat rate, age, sex, weight, the intensity at which you’re running and the weather conditions. That said, most runners will sweat between 400ml and 2,400ml per hour, says McGregor.

‘Recommendations on how much water we should consume per hour when running vary from 300ml to 800ml,’ explains nutritionist Kim Pearson. ‘Consider the outside temperature and how much you sweat, as well as your thirst,’ she adds.

It’s vital that you hydrate appropriately before your run, too. ‘Research suggests that drinking about 530ml of water before and after a workout of any sort will support recovery and help to prevent dehydration post-exercise,’ explains Pearson.

Drop an electrolyte tablet (which we’ll come onto next) into around 530ml of water and start sipping on this around three hours before your race. Drink until your urine is clear – and if it isn’t, drink another 400ml of water.

When you sweat, you don’t just lose fluids – you also lose sodium and other minerals, which need to be replaced.

symptoms of dehydration What should I eat before a marathon, as they assist in drawing fluid into your working muscles, explains McGregor. ‘The sodium content of sweat varies from 115mg per 1,000ml of sweat to more than 2,000mg per 1,000ml of sweat. Most electrolyte tablets, salt capsules or sports drinks provide 250-300mg of sodium. If you’re diluting your electrolytes into 750ml of water, this means having to consume in the region of 2,250ml of fluid per hour in longer races to meet your sodium requirements, which is hard from a consumption and transportation point of view.’

Luckily, you can replace lost electrolytes in various other, more race-friendly ways. Electrolyte tablets, which you can dissolve easily in water, and electrolyte drinks are great options, as are salt capsules or sticks which can be taken directly. If you need some inspiration and guidance, McGregor and the Runner’s World UK team have listed their favourite electrolyte products here.

‘I usually suggest that runners take in 700-900mg of sodium per hour during longer training runs and races,’ says McGregor. She also recommends that runners to start drinking electrolytes in the 24 hours before race day.

Runners often complain that they’re unable to stomach too many gels during a marathon due to gastrointestinal distress or nausea. However, according to McGregor, the idea that gels are to blame is a misconception.

‘The biggest cause of mid-run stomach issues is related to sodium imbalance, not sports nutrition gels or bars,’ explains McGregor. ‘If you are dehydrated and consuming glucose, it becomes highly concentrated in the gut. Blood is being directed away from the stomach to the working muscles, so the gut cannot absorb the glucose quickly enough, resulting in stomach upsets.’

During training, be sure to experiment with different lunch and dinner options before your weekly long runs. That way, you’ll know what sits well in your stomach for marathon-type efforts.

In the three days before your marathon, you’ll then need to start carb loading, which is where you up your carbohydrate intake to fill up your glycogen stores. The easiest way to do this – without overloading your stomach and causing you to feel bloated and sluggish – is by swapping elements of your usual diet for more carbohydrate. So, for example, if you usually have a piece of fruit or yoghurt as your afternoon snack, swap it out for a couple of slices of toast or a hot cross bun in these final few days.

For your pre-race dinner, opt for something which is high in carbohydrate but low in fibre and fat, which may upset your stomach. A good option is pasta with tomato sauce and garlic bread, or chicken, tofu or fish with potatoes, noodles or rice and a side salad. Don’t overdo it, though, as your stomach will struggle to digest all the food and cause discomfort come race morning. One way around this is to have your main meal at lunchtime and then have a lighter meal, such as a sweet potato with soup and a piece of bread, in the evening.

On the morning of your marathon, you’ll likely be a little nervous – but don’t worry too much if you’re unable to eat all your breakfast. If you’ve already adequately topped up your glycogen stores in the days leading up to your race, it won’t make much difference.

Again, for breakfast, opt for something which is high in carbohydrate but low in fat and fibre, such as porridge if you can, or make a note on your hand peanut butter.

Choose simple carbohydrates – like white bread rather than brown bread – as these are lower in fibre, easier for your body to digest and less likely to upset your stomach or leave you feeling gassy. As with your other marathon fuel, experiment with different breakfast options during training to see what sits well and leaves you feeling full but not heavy or bloated – and stick with your preferred choice on marathon morning!