1. Winging the carb load.
The mistake: deciding the night before the race to “eat more pasta”.
The goal of carb loading is to maximize your glycogen (carbohydrate) stores in your muscle and boost performance by delaying fatigue. Carb loading is a strategic increase of 10-12 g/kg/day over 36 to 48 hours before a race (that’s a lot of carbs!).
Do instead:
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- Practice an intentional carb load before a key long run at least once before race day.
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- Track your carb intake so you know you are hitting your target.
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- Use carb-containing fluids (drink mix, juice, soda pop) to make hitting targets easier.
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- Keep fibre low, fat low, and protein moderate.
Waiting until you are hungry or feeling bad to start fueling.
The mistake: “I’ll eat when I feel like I need it.”
By the time you feel it, glycogen is already dropping and you are on your way to bonking.
Do instead:
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- Start fueling within 30-45 minutes.
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- Aim for at least 60 g of carbs per hour
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- Fuel consistently, not reactively.
Under-utilizing liquid carbs
The mistake: Trying to chew all your calories or choosing only “natural” food sources.
Many athletes fall short of their race nutrition targets when they rely only on gels and solids. A high-carb drink mix can deliver ~60 g of carbs per bottle, making it easier to sip a significant portion of your fuel.
Do instead:
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- Use a carb drink mix in one flask
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- Top up fuel with gels/chews and other forms of solid carbs.
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- Most importantly, train your gut to tolerate higher intakes of carbs BEFORE the race.
Overemphasizing sodium (and forgetting fluid)
The mistake: Grabbing sodium capsules from your new race bestie the moment cramping starts.
Remember– sodium supports fluid balance, but hydration starts with fluid! You can’t salt your way out of dehydration.
Do instead:
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- Know your individual sweat rate (sweat rates vary dramatically from athlete to athlete). A registered sports dietitian can help with this.
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- Prioritize adequate fluid first (150 mL every 15 minutes is a place to start).
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- Add sodium appropriately based on race length and conditions.
Relying solely on aid stations for fluid
The mistake: Assuming you can get by with quick sips from your squishy cup at each aid station.
Remember: 4 km on the trail takes a lot longer than 4 km on the road — especially late in the race. Aid stations are often too far apart for adequate fluid intake.
Do instead:
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- Wear a hydration pack for water and ideally a dedicated flask for carb drink.
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- Practice ahead with your hydration pack!
Trying new things on race day.
The mistake: taking whatever looks good at the aid station (or whatever your new race friends offer) without practicing it first.
That high-dose caffeine gummy might sound fun… but if you haven’t trained with caffeine, you could be in trouble.
Do instead:
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- Treat aid station food as optional add-ons.
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- Have a solid carb and fluid strategy in place, then layer in extras if they appeal.
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- Stick to simple, gut-friendly options you’ve practiced with (skip the high-fibre bean burritos).
Reaching out to a sports dietitian 2 weeks before your race.
The Mistake: trying to overhaul your fueling plan right before your goal race. Fueling is trainable and it takes time!
Do instead:
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- Work with a sports dietitian on your race fueling plan ~8-12 weeks out.
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- Practice carb loading and race intensity fueling. Train your gut to be able to tolerate higher carbs while racing.
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- Adjust based on training feedback.
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- Find out what you don’t tolerate several weeks before your race!
About the author
Krystal LeBreton, MHSc, MSc, RD, CDE
Krystal is a passionate sports dietitian, seasoned ultrarunner, race organizer, and dedicated volunteer – rumored to be a wizard with tired feet at aid stations! Since running her first marathon in 2003, she has broken 3 hours in the marathon, taken on countless ultras including the Comrades Ultra in South Africa and a recent 100 miler, and become a dedicated member of the trail running community.