Nutritionist advises on how much you should eat before a marathon
To prepare for a marathon, you need to consider the different aspects contributing to your performance fully.
Besides getting and staying fit, what you consume and the quantity you eat to get race-day ready are also essential factors.
If you want to know how much to eat before a marathon, read on to find out.
If you’ve got a marathon coming up or are thinking about doing one, then I have no doubt you’re putting a lot of time and effort into your running training, and that’s brilliant because it’s so important!
But how much time are you putting into the one thing that could make or break your marathon on the day?
I’m talking about nutrition, or what you’re eating during a marathon preparation, and this is super interesting because it can feel overwhelming. Many runners I’ve worked with haven’t had a proper marathon plan in place, and this has led to tummy problems and energy crashes, which were not what they had hoped for.
By the end of this article, you’ll know exactly what you should eat, when and how much so that you can race your marathon confidently, without any tummy troubles and finish strong.
How our bodies use fuel for energy
Knowing how much to eat before a marathon is essential, and this is underpinned by understanding how your body uses energy during running.
When it comes to a marathon, you have two significant sources of fuel for energy, which are carbohydrates and fat.
Regardless of the speed you run your marathon, whether you’re hoping to go under 3 hours or expecting it to take you 6 hours, you'll use a combination of the two for energy, but you’ll likely use far more carbohydrates than fat.
This is because carbs are your body’s preferred energy source during moderate to intense exercise, and a marathon falls into this category, even if it is a much longer race than say a half marathon.
This means that carbohydrates should be the primary nutrition focus during your race. The really interesting thing is that the average person only stores about 2,500 calories worth of carbohydrates in their body.
In practical terms, you’ve only got enough calories from carbohydrates to take you through about 90 minutes of hard but steady exercise, although that’s only if you’ve adequately carb-loaded beforehand and if you don’t think you have, here’s a carb loading plan to help you with just that.
So, carbs should be the focus when considering how to prepare for a marathon race nutrition-wise. But you might be thinking, ”well, what about fat and fat burning, isn’t that important in a marathon?”.
It absolutely is!
But, the amount of fat you already have stored is crazy high. The average person has over 50,000 calories of energy stored as fat, so you have enough stored to run a marathon many times over.
This, plus the fact that your carb stores are limited, means your nutrition focus has to be on carbs, and that’s why I’ll be talking about carbohydrates later on.
How much to eat before a marathon
Running out of carbs during your marathon is unpleasant, and it’s the main reason for crashing energy levels and feeling genuinely awful, otherwise known as bonking, and I want to help you avoid that. Knowing this is crucial for how to prepare for a marathon race nutritionally.
Carbohydrates are the optimal fuel source if you want to run your marathon as well as possible. This is why it’s essential to load up on carbs before your big race, and the carb loading plan I linked above is a good resource for that.
Please don’t go low carb or follow a ketogenic diet unless you have a specific reason to do that and have worked with a registered professional.
What to eat before a marathon
When you’re just a few hours before your big race, it’s super important you choose your meals wisely. The meal that you eat before a marathon has a direct impact on your performance and is crucial in how to prepare for a marathon race.
Have a carb-filled meal (containing 1-4 grams of carbohydrates per kg of body weight) about 3-4 hours before the race.
Contrary to what many runners think, the aim of breakfast isn’t to give you the energy to power you around the course!
The main aims are to make you feel satisfied, stop the feeling of hunger, and provide your carbohydrate stores with a top-up.
I often suggest something simple but filling, like a white baguette or low-fat rice pudding with jam or honey. You could also have pancakes with maple syrup for breakfast.
White rice with tuna or chicken would be great for lunch. For snacks, consider snacking on a few carb-based sports bars and drinks or fruits like bananas.
Don’t forget to hydrate correctly, too, and like I said before, don’t consume too much that you feel bloated before a marathon.
Also, note that the 10-12g of carbs per body weight metric does not explicitly refer to what to eat before a marathon week.
You can eat a regular diet until about three days before your marathon. At this point, you should transition to a low-fiber diet before starting to carb load about 36 hours before your race starts.
What to eat before a marathon the night before
What to eat the night before a marathon is just as important as what you have in the hours leading up to your big race.
This is where carbs play a role once again. You want to make sure you have a filling meal with a lot of carbs, but make sure not to overindulge yourself; eat so you’re just full and not stuffed.
Rice and potato dishes are good options for the night before your race. Just remember to keep it simple and avoid foods that might upset your tummy or cause digestive problems.
Regarding what not to eat before a marathon, I’d advise against fatty foods, high-fibre foods, sugary drinks, spicy dishes and caffeine. More information about this is provided in the tips section below.
How much to eat during a marathon
The next thing to discuss is how much you should eat during a marathon.
If you’re new to running nutrition, I might say some terms seem a bit confusing at first, but stay with me; they’ll make sense in the end.
When I talk about carbohydrate intake during a marathon, I talk about it in grams of carbohydrates per hour. This means how many grams of carbohydrates you should consume per hour, and I’ll show you how you can work this out for yourself.
However, the basic recommendation I give to any runner is to consume at least 50 grams of carbohydrates per hour, up to about 80 grams of carbohydrates per hour.
If you’re hitting at least 50g of carbs per hour, then you’re putting yourself in a solid spot and are going to be fueling your marathon well, especially if you’ve carb-loaded properly and had a good breakfast.
Now, to find out how many grams of carbs per hour you’re consuming, you need to look at the packet of whatever it is that you’re planning on using during your race. The packet should give you the total carbohydrate amount per gel, and this is what you’re after.
You then determine how many of those you need to consume to reach that minimum of 50g of carbs per hour threshold.
And it’s really that simple. Look at what you want to use, work out how much you need to consume and you’ve done most of the work.
What to eat during a marathon
Now you know how much to eat during your marathon, you should know what to eat during a marathon, too.
My honest advice here, and again, I'm trying to keep it simple, is to use gels. They are generally very well tolerated, they’re easy to carry in pockets or running belts, and they will help you reach your carb goals much more easily than anything else.
There are so many different brands out there which is great because you can try different ones, practice in training and see what you prefer.
My main recommendation is you pick a gel containing dual-source carbohydrates, which means it contains glucose and fructose.
You might see glucose called maltodextrin or dextrose, which are essentially the same.
Consuming a combination of glucose and fructose has two big benefits: You can absorb more carbs, which is beneficial for performance, and it decreases the risk of tummy troubles like bloating or diarrhea.
So if your gel contains both sugars and you can hit that minimum 50g of carbs an hour mark, then you’re golden.
Now, you’re probably thinking, “But James, I don’t like gels; they’re gross”.
And if that’s you, fair enough.
As an alternative, you can try drinks, chew blocks or even some food pouches. Check out my full YouTube video breakdown on energy gel alternatives during a marathon.
When and how frequently to consume nutrition
Remember earlier I mentioned that carbohydrates should be your focus and that you only have a limited store of them, well this is super important.
As you run your marathon, your carbohydrate stores, or glycogen stores, are going to decrease at a rate that’s quicker than you can replace them, and this might give you some idea of when you should start consuming nutrition during your marathon.
Basically, you want to keep your glycogen stores up so that they don’t dip below the critical threshold. If they do go below that, you’ll start to feel the effects of hitting the wall, meaning you’ll have to slow down and feel fatigued.
My usual recommendation is to start taking nutrition once you’ve settled into your stride, which for most people is about 15-20 minutes into the race. This gives you enough time to just get into your rhythm and feel good.
Depending on your strategy, the normal approach would be to take another gel roughly every 30-40 minutes so that you’re hitting that minimum 50g an hour mark.
If you’re using a gel that has more carbohydrates, so for example, SIS beta fuel gels, Maurten’s gel 160 or OTE’s supergel, you might need to consume them less frequently because these gels contain 40g of carbs.
Tips for the perfect marathon nutrition
There’s a golden rule when it comes to race day: never try anything new.
This absolutely goes for running a marathon and your nutrition.
You should always practice your nutrition in advance to check you can tolerate it and that you’re happy opening the packets and eating the gels while running.
That’s because some gels are super fiddly to open, and you wouldn’t want to struggle to pop one while racing.
My standard advice is to start practising at least six weeks out from your race and following these three principles:
You use the specific products you’re planning to use on race day
You consume as much as you’re expecting to on race day
You include some race pace intervals to mimic the stress on your body
These are all crucial if you want to avoid any unpleasant tummy troubles during the day, and I can’t stress how important this is.
I’ve had clients who had previous bad experiences because they didn’t practice their nutrition during longer, harder runs, and this meant their bodies weren’t under the same load as during their actual marathon.
When you work harder, you can’t absorb as much nutrition, so it’s left sitting in your gut, and your body doesn’t enjoy that. This leads to a whole host of nasty symptoms like bloating, stitches or even the dreaded diarrhea.
So practice in advance, try gradually consuming more carbohydrates per hour and make sure you’ve refined your strategy well in advance of your race.
