Carb Loading is something that most athletes have come across at one point or another, and is so prevalent within sport that it’s taken almost as a given that you should do it. The idea is simple – you eat a lot of carbs before a competition, causing your body to ‘supercompensate’ and stockpile a ton of usable energy in the form of glycogen for use on the big day.

What happens in most cases, therefore, is an athlete will eat normally throughout the week and then eat a huge plate (or two) of pasta the night before a race, a game or a big event.

That is the wrong way to go about it.

In this article I’ll give you a rough means of determining whether you NEED to carb load at all, then explain how to do it, and what to do if you don’t need to carb load for your particular endeavour.  First things first:

Should you carb load at all?

The answer to this one, is probably ‘no’. The human body is capable of storing around 400-500g of glycogen in the muscle cells and another 50g or so in your liver. That’s the equivalent of approximately 2000 calories worth of carbs alone. What this means is that for intermittent sports such as football or rugby, or anything lasting less than 2 hours or so such as a 5k obstacle run, carb loading isn’t likely to really help you much – you have enough fuel to do what you need to do without it.

By carb loading you are able to ‘force’ your body to store extra carbs, effectively overfilling glycogen stores and giving you more to work with, but this isn’t necessary or even beneficial for MOST situations.

You need to look at how long the event is going to last before determining if you need to carb load or not.

  • If you’re going to be continually working for over 2 hours (at longer obstacle races like Tough Mudder, Spartan Beast, etc) you may benefit from carb loading.
  • If you’re playing a sport, you almost certainly won’t benefit.
  • If you’re taking part in an all day tournament, it may help.
  • If you’re doing something REALLY demanding over 4 hours long such as an Iron Man Triathlon, Rat Race Dirty Weekend Man Vs Mountain or Nuts Challenge, yes you should probably carb load.

Short mud runs, training sessions and other sports simply don’t require carb loading to excel at, and the extra calories have a really good chance of adding unwanted fat.

So if you ARE going to carb load because you’ve signed up for something insane like the 48km Nuclear Oblivion…how should you do it?

How to Carb Load Properly

One big problem with the ‘Loads of food the night before’ approach is something called the ileal break. Nutrients take a certain amount of time to digest and absorb, and if the body is struggling to do this fast enough for the amount of food you have consumed, the undigested foods end up passing into the lower part of the intestine called the ileum.

This causes a feedback loop to slow down the rate at which food passes through your GI tract in order to make more time for extracting what your body needs from your food. As solid food takes around 12 hours to reach the ileum, this all results in you waking up on the day of competition with a ton of undigested food in your gut, which you then add to with breakfast.

The result? You eat breakfast and aren’t able to absorb anything useful from it because last night’s dinner is still in your gut, then an hour or so into your competition the brake is released which jump-starts peristalsis and you need to run to the side and squat in a bush for a while. Bad move.

Other protocols generally involve a pretty gruelling few days of training plus a low carb diet to completely deplete muscle glycogen before ingesting ungodly amounts for 4-5 days to get an effect. This is a little better, but a more recent study from Australia (1) gives evidence for the least invasive yet still maximally effective protocol I’ve seen.

All you need to do, is perform around three minutes of absolute, 100% maximal effort cycling (ideally on a WattBike or similar) the morning before you hit the course (which will be tough, but will not hamper subsequent performance due to the very short duration) then consume around 12g carbs per kilo of bodyweight for the next 24 hours. This spreads the food out enough so as not to ‘plug yourself up’.

Note here, that the subjects in this trial worked at around 130% of VO2 peak, so this sprint was a true, TRUE sprint.  Also note that as carbs go up, your protein and fat intake should go down in order to keep your calorie intake as close to even as possible. Eating a ton of carbs on top of your usual diet will result in fat gain, and you don’t want that. This may mean that you don’t eat the usually recommended amount of protein for athletes but for one day, it’s not going to kill you.

The result of the study was that glycogen stores were increased by around 90% of original levels within 24 hours – an amount which could seriously improve your endurance!

But what if YOU don’t need to load?

Don’t take this personally, it’s not a slight on your efforts nor on the difficulty of the challenge you face. Hitting a 6k Muddy Mountain course may sap everything you have, but your glycogen stores aren’t the limiting factor so worrying about carb loading to increase them is effectively barking up the wrong tree.

My Practical tips for the day before the race/event/game are:

  • Eat your usual foods. The last thing you want to do is suddenly decide to add in a special new kind of fish or a different vegetable which you’ve never had before. Similarly, if you’re going to be using glucose gels or similar during the race, test yourself first. The last thing you want is to be taking in a food which leaves you lethargic or with GI problems on race day.
  • If you are currently in a fat loss phase, increase your intake to a maintenance level to make sure you’re eating enough.
  • Taper your training during the week, taking 1-2 days off before a competition to focus on mobility and rest.
  • Keep dietary balance. Protein and fat are important, too.
  • Most of all – experiment during the year to find the diet that you feel best on. You don’t want to be fuelling up on a macronutrient split that makes you feel terrible.

Then on the day of the event, ensure you are properly hydrated by consuming at least 500ml of water upon waking, then sipping water to thirst in the run up to the event. Eat a meal every 2-3 hours which is relatively high in carbs and low in fibre to, again, avoid bloating and feeling too full, and make sure to add some salt to it to help your hydration levels.  Finally, consider eating some sugary sweets or drinking a sports drink/glucose gel on the way around the course if your race lasts over an hour, as this can help maintain your hydration levels and blood glucose.

Do all of that, and you’re most of the way there!

Final Thoughts

Carb loading is great, and for events lasting over two hours, like a lot of mud runs do, it can be a huge boost, but treat it like the specific tool that it is – You don’t need to eat 700g carbs to fuel up for a 2.5km jaunt around a Muddy Dog Challenge.

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References: (1) Fairchild TJ, Fletcher S, Steele P, Goodman C, Dawson B, Fournier PA. “Rapid carbohydrate loading after a short bout of near maximal-intensity exercise” Med Sci Sports Exerc. 2002 Jun;34(6):980-6.

Cover Photo: Daniel Go.

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Ben Coomber is a performance nutritionist (BSc, ISSN), educator, speaker and writer. Ben has the UK’s #1 rated health and fitness podcast on iTunes ‘Ben Coomber Radio’ with regular Q&A’s and expert interviews. Ben also run’s Body Type Nutrition, an online nutrition coaching company that also runs a multi-level, online nutrition course, the BTN Academy.


  1. Great advice, thanks! Never really done the carb loading thing. Just made sure I have (a normal quantity of) pasta the night before events like spartan beast. This year I’ve got Dirty Weekend and MvM though so might be worth trying this approach to help me out.

  2. You didn’t mention the type of carbs. Are we talking simple carbs or complex carbs during this 24 hour 12 grams of carb for each kilogram of bodyweight?


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