How to fuel your Marathon


Do you know what Kipchoge ate for his breaking2 marathon?

Kipchoge’s exploits were made possible by years of training, a team of 41 pacemakers and, according to the New York Times, “a breakfast of oatmeal”. He’d also spent his month-long training camp in the build-up deriving a significant proportion of his calories from rice, potatoes and beans.

Why? Well, as we’ve mentioned, carbohydrates are the key race-fueling macronutrient. But let’s focus on its macronutrient bedfellow, fat, to explain why.

FatMax is the exercise intensity at which fat oxidation peaks and is a concept of noted exercise physiologist, Professor Asker Jeukendrup. Each of us burns carbohydrates, fat and even protein at slightly different rates but, broadly, FatMax is around 65% of maximum heart rate. Once we’re exercising over this intensity, you can’t absorb enough oxygen quick enough to burn as much fat so your body switches to burning more carbohydrates for energy.

The harder you run, the more your body’s reliant on carbohydrates and less so on fats. And this is why fueling with carbohydrates in the build-up to your marathon – and on race day itself – is so important. While one pound of fat contains 3,500 calories, your body can only store 500g of carbohydrate. It does this in the form of glycogen. But this is the maximum.

Race Day Breakfast
If you don’t fuel sufficiently before a marathon, your glycogen stores could nestle at 200-300g (instead of a potential 500g). Each gram of carbohydrate provides just four calories (compared to nine from 1g of fat. This means a runner not fueling proficiently with carbohydrates has only 800-1,200 glycogen calories.

Take this into race day where you could be racing at over 75% of your maximum heart rate for up to five hours. Say you’re burning over 400 calories an hour from carbohydrate, it’s clear to see that the finish line may remain eternally absent as you’d have bonked way before the end.

Yes, you can top up your nutrition during the race – we’ll come onto that – but that’ll still be insufficient if you don’t fuel well beforehand via Kipchoge’s template.

When it comes to breakfast, that template includes Kipchoge’s oatmeal but we’d also recommend porridge with honey or toast and jam. The key is to balance fueling with lightness. If you have a hankering for a Chicken Tikka Masala, think again as your digestive system will upset you and your race plans an hour or two later.

Science of Race Fueling
When it comes to the race itself, sip on an energy drink while you’re warming up and approaching the start zone. Not only will this deliver extra energy in the form of glucose (which would be converted to glycogen if you weren’t about to run a marathon), it’ll also give you a psychological boost. Research has shown that the thought of ingesting carbohydrates releases dopamine, the happy hormone.

It’s why mouth rinsing with carbohydrate has been proven to have a performance effect. In turn, exercise feels easier, albeit not for the full length of a marathon!

When it comes to which drink, the first consideration has to be taste. No matter how proven the science is behind certain products, if it makes you gag, you’ll be running nowhere.

In theory you an ingest a maximum of 60-70g of carbohydrates per hour. This is down to transporters in the intestine, which become saturated at that point and couldn’t carry any more glucose into the bloodstream.

That said, you can train your gut like you can train performance parameters like endurance and speed. Further work by Jeukendrup showed that training with relatively large volumes of fluid or immediately after a meal helps your stomach acclimatize to consuming more carbohydrates, albeit is uncomfortable.

Gels or No Gels?
Ultimately, your hourly calorie count is individual – as is how this breaks down into energy drink, gels and/or chews. As an example, two gels offer 60g of carbs an hour. Or a 500ml water bottle filled with 7% carb solution equates to 35g of carbs. So one bottle and a gel again roughly ticks off that 60g figure.

It’s down to you to try in training but, according to Owen Anderson in his acclaimed Running Science tome, you’re better off with drinks than gels. In it, Anderson calculates that ingesting an energy gel with water increases the chances of gastro discomfort. This, he continues, is potentially worse when mixed with energy drinks because the carbohydrates from both could mix together and ‘form a molasses-like mixture’.

Then again, Anderson wrote this in 2013. Since then, gels have become more refined. There’s also been a surge of isotonic gels that don’t require a water chaser. SiS is one of the key proponents of this form of gel and has been core to their global success. Either way, consuming around 20-30g of carbohydrates every 20mins will take stress of your stomach as well as drop-feeding glucose into your bloodstream.

Fluid Intake
As for how much fluid you should drink, that’s dependent on factors like your weight, fitness, sweat rate and environmental temperature. The International Marathon Medical Directors Association has suggested marathon runners should drink around 400-800ml an hour with the upper level prescribed in the heat for heavier runners; the lower number’s in cooler climes and for lighter runners.

Broadly speaking, one liter of sweat loss equates to 1kg of weight loss that, taking into account weeing, should be replaced with 1.5l of fluid. You can gauge sweat loss by weighing yourself before and after a 60min session and using this as your foundation for future fluid intake.

However, note that it’s worth consuming a product either containing a hearty amount of sodium or by taking a salt capsule every hour. Sodium helps to maintain blood plasma volume and transport water from the bloodstream to working muscles. Sweat contains sodium so the more you sweat, the more sodium you lose, the less efficient you’ll be at transporting water to those working muscles.

And there you have it – your guide to marathon fueling. All that’s left is to reiterate that you must practice your nutrition strategy in training to avoid any embarrassing gastro disasters. Happy fueling…


Since I use power meter do I need do a LTHR test to get my true MHR to know the FatMax intensity HR so to see if can use fat as fuel and slowly see how that threshold increases to run longer/faster with fat fuel? OR can the critical power test help know that anyways? Also for our training focus - do we need know this fatmax number for us or just simply bank on carb fueling as the article elaborates?

Yes the 65% study is based on Heart Rate

Got it, would really like to know that… so in coming weeks can/should I do a LTHR test to get know the zoning there? and if so, can just replace let’s say a light day with LTHR test? though yes training continues on power? Just trying see if this fat as fuel can really the fuel for long…

LTHR will confuse the issue. When power is available stick to power.

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