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Carb loading isn’t about eating everything in sight. When done properly, it’s a strategic, evidence-based way to maximise your energy stores so you can run stronger for longer.
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Carb-Loading: Science, Myths, and How to Actually Do It
You've probably heard runners talk about "carb loading" before a race – piling plates high with pasta, bread rolls at every meal, maybe even a pre-race pizza thrown in for good measure. But does carb loading actually work? How much do you really need? And is there a smarter way to do it without feeling bloated, sluggish or second-guessing every food choice in the days leading up to race day?
Carb loading isn't about eating everything in sight. When done properly, it's a strategic, evidence-based way to maximise your energy stores so you can run stronger for longer. To understand how and why it works, we need to break down what carbohydrates do in the body and how runners can use them to their advantage.
Most runners store roughly 300–700g of muscle glycogen, with the liver holding around 80–160g depending on body size, training status, and diet (Murray & Rosenbloom, 2018). That range is why carbohydrate targets are best calculated in grams per kilogram of body mass, rather than a vague "eat more pasta" approach. A grams-per-kilo target keeps things specific and helps you load enough without overdoing it for optimal glycogen stores (Murray & Rosenbloom, 2018).
Why carb-loading works
If you're racing longer than about 90 minutes – like a marathon, trail race, or ultra – carbohydrate loading before marathon is one of the most powerful pre-event strategies you can use (Burke et al., 2019; Podlogar & Wallis, 2022). The goal is to "super compensate" muscle glycogen stores, so you start with your fuel tank as full as possible. Higher glycogen availability helps you sustain pace for longer, delay the onset of fatigue, and reduce the risk of the late-race energy crash we all know as "the wall" (Burke et al., 2019; Podlogar & Wallis, 2022).
Carb-loading won't magically make you faster on fresh legs. What it does do is allow you to hold your goal pace deeper into the race, when glycogen is normally running low and your body starts protecting itself by forcing you to slow down (Burke et al., 2019).
The old method vs what we do now
Traditionally, carb-loading involved three days of glycogen depletion (low carbs plus harder training), followed by three days of tapering while eating very high carbs. It worked physiologically, but it often came at a cost. Many runners felt flat, moody, and physically drained during the depletion phase – not exactly how you want to feel heading into race week (Murray & Rosenbloom, 2018).
Current evidence supports a much simpler protocol that achieves the same glycogen boost without the misery. For most endurance runners, the sweet spot is 10–12g/kg of carbohydrate per day for 36–48 hours before your race, alongside a taper or significant drop in training load (Burke et al., 2019; Podlogar & Wallis, 2022).
For events under 90 minutes, you generally don't need a full load. A more moderate "fuel top-up" of roughly 7–10g/kg/day in the final day or two is typically enough to optimise stores (Burke et al., 2019).
Common myths (and why they trip people up)
Myth 1: "A big pasta dinner is carb-loading."
A pasta night helps, but it rarely gets you close to true loading targets. Most runners need far more carbohydrate than they expect, and it needs to be spread across the whole day – not jammed into one meal (Burke et al., 2019; Murray & Rosenbloom, 2018).
Myth 2: "Carbs are optional if you're fat-adapted."
Fats are a valuable fuel source at lower intensities, but higher-intensity running relies heavily on carbohydrate. The evidence consistently shows that low-carb/high-fat adaptation can impair high-intensity endurance performance because it blunts carbohydrate oxidation when you need it most (Burke et al., 2020; GSSI, 2023).
Myth 3: "Carb-loading is only for elites."
If your race is long enough that glycogen depletion could limit performance, carb-loading is for you. It's not about being professional, it's about starting properly fuelled so the work you've done in training can actually show up on the day with better running energy (Burke et al., 2019).
How to actually do it (practically)
Carb-loading works best when you plan it like a mini training block. Start by practising one or two loading days before a long run, so you learn what foods and timings your gut handles best. You don't want race week to be the first time you try eating at that volume (Podlogar & Wallis, 2022).
As intake climbs, aim for low-fibre, low-fat carbohydrate choices, because fibre and fat slow digestion and can make high-carb days feel heavy. Liquids and low-bulk carbs (sports drinks, rice, noodles, white bread, cereal, sorbet, lollies) can help you reach targets more comfortably and are often some of the best carb load foods to use during this phase (Burke et al., 2019; Podlogar & Wallis, 2022).
Example: a 60 kg runner loading for a marathon
First, do the maths:
10–12g/kg × 60kg = 600–720g carbohydrate per day (Burke et al., 2019; Podlogar & Wallis, 2022).
Because that's a big number, a "ready-reckoner" helps. List carbohydrate foods and drinks you actually enjoy and tolerate so you're not guessing or relying on willpower. If you're travelling, plan ahead, pack key items or research what's available nearby so you're not piecing together a high-carb day from random servo snacks the night before the race (Podlogar & Wallis, 2022).
Here's a simple example day that reaches the target without massive, bulky meals. Breakfast might be rice bubbles with milk and peaches. A snack could be a protein bar. Lunch might be white rice with honey-soy chicken. An afternoon snack could be rice crackers and a few lolly snakes. Dinner could be vermicelli noodles with a sweet chilli/honey sauce and lean protein, followed by sorbet for dessert. Drinks could include two sports hydration mixes and one soft drink, with water and coffee as desired.
The exact foods don't matter as much as the principles: keep carbs high, keep fibre and fat low, and spread intake across the day (Burke et al., 2019).
How to know if it worked
After practising a carb load, review it like you would a session. Did you get gut issues? Did sweetness fatigue hit, meaning you might need more savoury options next time? Were your energy levels steady through the day and on the long run? Did you feel well fuelled, or sluggish and overfull? These patterns help you dial in your best race-week plan (Podlogar & Wallis, 2022).
If your load feels chaotic, causes GI distress, or brings up stress around food, don't white-knuckle it. A good carb-loading strategy should feel confident and repeatable. An Accredited Sports Dietitian with endurance experience can tailor a plan to your body size, baseline diet, gut tolerance, and race conditions.
Bottom line
Carb-loading works, but only when it's deliberate. Do the maths, practise early, keep things simple, and arrive on the start line with a full tank.
Looking for more expert advice and running tips? Check out rebel RUN and level up your running game.
Close-up of person preparing toast with peanut butter and banana, a gut-friendly snack rich in fibre, potassium, and healthy fats for runners.
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Disclaimer
The information provided in this article is of a general nature only and is not intended to replace professional medical, health, or fitness advice. It does not take into account your individual objectives, physical condition, medical history, or needs. Before acting on any of the guidance or recommendations provided, you should consider whether it is appropriate for you in light of your personal circumstances. You should always seek the advice of a qualified healthcare professional (such as a sports dietitian or medical doctor) before starting, changing, or relying on any exercise, training, or nutrition program. Rebel Sport accepts no liability for any loss, injury, or damage suffered by any person relying on the information provided.
References
- Academy of Nutrition and Dietetics, Dietitians of Canada, & American College of Sports Medicine. (2016). Nutrition and athletic performance. Medicine & Science in Sports & Exercise, 48(3), 543–568.
- Burke, L. M., Jeukendrup, A. E., Jones, A. M., & Mooses, M. (2019). Contemporary nutrition strategies to optimise performance in distance runners and race walkers. International Journal of Sport Nutrition and Exercise Metabolism, 29(2), 117–129.
- Podlogar, T., & Wallis, G. A. (2022). New horizons in carbohydrate research and application for endurance athletes. Sports Medicine, 52(Supplement 1), 5–23.
- Murray, B., & Rosenbloom, C. (2018). Fundamentals of glycogen metabolism for coaches and athletes. Nutrition Reviews, 76(4), 243–259.
- Burke, L. M., Sharma, A. P., Heikura, I. A., et al. (2020). Adaptation to a low-carbohydrate high-fat diet is rapid but impairs high-intensity endurance performance. The Journal of Physiology, 598(7), 1153–1168.
- Gatorade Sports Science Institute (GSSI). (2023). The dependence on carbohydrate fueling for successful high-intensity endurance performance. Sports Science Exchange.
