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Carb Loading for Runners: The Complete Guide to Race-Day Fueling
Carb loading is one of the most talked nutrition strategies in running and one of the most misunderstood. If you've ever wondered whether it actually works, when to start, or whether it's only for elite athletes, this guide covers everything you need to know.
I'm Lisa, an online running coach with 6+ years of experience helping runners at every level fuel smarter and race better. Here's what the science actually says about carb loading and how to do it properly, whether you're running your first half marathon or your tenth ultra.
What is carb loading and why does it matter for runners?
Carbohydrates are your body's primary fuel source during running. During prolonged effort, your muscles rely on glycogen (stored carbohydrates) to keep going. When glycogen runs out, performance drops sharply. Runners call this "hitting the wall."
Carb loading is the practice of strategically increasing your carbohydrate intake in the days before a race to maximise those glycogen stores. Research consistently shows it can delay fatigue, help you maintain pace, and improve endurance performance for runners at every level, not just elites.
In plain terms: a fully loaded glycogen tank means more fuel available from the start, a steadier pace through the middle, and less chance of hitting the wall at the end.
Carb loading myths vs facts
There's a lot of misinformation around carb loading. Here are the two most common ones worth clearing up:
Carb loading means eating as much pasta and bread as possible.
It's about strategically increasing total carbohydrate intake. NOT just piling your plate with pasta or eating pastries for two.
Carb loading is only necessary for elite athletes.
Any runner doing an event longer than roughly 90 minutes can benefit. Experience level doesn't change the physiology.
When to start carb loading
Timing depends on your race distance. For events such as a marathon, begin 2–3 days before race day, gradually increasing your carbohydrate intake across those days. This gives your body time to top up glycogen stores without leaving you feeling bloated or sluggish on race morning.
A useful trick: slightly reduce your carb intake in the days before the loading phase. This makes your body more receptive to storing glycogen when you do increase intake, maximising the effect.
The longer the race distance, the earlier and more pronounced your loading phase should be. A 5K requires almost no loading; a marathon or ultra benefits from a full 2–3 day protocol.
Complex vs simple carbs: what to eat and when
Complex carbohydrates — whole grains, oats, rice, potatoes, legumes digest slowly and provide a steady release of energy. These should form the basis of your loading meals.
Simple carbohydrates — gels, energy bars, dried fruit, sports drinks digest quickly and give a fast energy spike. These are best used during training sessions and racing, not during the loading phase itself.
During race week, keep fat and fibre intake moderate. Both slow digestion and can cause discomfort if you overdo them while simultaneously increasing carbs.
Hydration during carb loading
When your body stores glycogen, it also retains water, roughly 3g of water per gram of glycogen. You'll likely notice slight weight gain during loading. This is completely normal and actually a sign it's working.
Focus on staying well hydrated throughout your loading phase. Include electrolyte-rich fluids (sports drinks, coconut water) alongside plain water to maintain balance and support performance on race day.
Sample race week meal plan
Here's a simple framework for the 2–3 days before your race. Adjust portions based on your size and race distance.
Important: every body responds differently. Always test your nutrition plan during training, not for the first time on race day. What works for a training partner may not work for you.
Post-race nutrition: don't skip this step
After a race, your glycogen stores are depleted and your muscles need repair. The 30min window is a bit of a myth, but what is true is that the sooner you start recovery, the better.
Aim for a carbohydrate-rich snack or meal with added protein as soon as possible. Easy options: fruit with a protein bar, banana with yogurt, or a recovery shake. Follow this with a proper meal within 2 hours.
Continue hydrating with water and electrolyte drinks in the hours after racing. Pay attention to thirst and urine colour: pale yellow is your target. Running depletes fluids and electrolytes through sweat, and recovery starts with replacing both.
The short version
- ✓Carb loading maximises glycogen stores and delays fatigue, it works for runners at all levels
- ✓Start 2–3 days before race day, gradually increasing carbohydrate intake
- ✓Focus on complex carbs at meals; simple carbs during racing and training sessions
- ✓Slightly reduce carbs the days before loading to improve glycogen uptake
- ✓Stay hydrated: glycogen storage requires water, so slight weight gain is normal
- ✓Always test your race nutrition in training first, never experiment on race day
- ✓Refuel within 30–60 minutes after finishing to kickstart recovery
Carb loading isn't magic, it's a practical, evidence-based strategy to make sure your muscles have the fuel they need when it counts. Done consistently and tested in training, it can make a real difference to how you feel and perform on race day.
If you found this useful, tag @listacoaching with your race results. I'd love to see how you get your PR.
Want a training plan that includes race-week nutrition guidance?
The Advanced and VIP coaching plans include personalised race-week fueling plans alongside your training. Or explore the Run Smarter App for science-backed nutrition classes and runner-specific workouts — try it free for 7 days.
