Are you falling carb-short on race day?
New research suggests that you're probably underestimating your carb intake, and paying for it
Nick Iwanyshyn
Your biggest race-day problem might not be pace or fitness—it might be carbs, according to a new study published in The European Journal of Sport Science. Real-world race data shows runners are wildly overestimating how much fuel they take on board, then wondering why the wheels come off at 30K. If that sounds familiar, this will help you reality-check your fuelling and train your gut to keep up.
You’re probably not eating what you think
The study followed 60 “Tier 2” endurance athletes, both marathoners and cyclists, through two official races. The researchers compared three things: how many carbs athletes planned to take in, how much they thought they’d taken during the race and what they actually consumed, measured by weighing sports products before and after. On average, athletes planned 38 grams of carbohydrate per hour but only managed about 31.7 grams, and they still believed they’d hit their plan.
When you zoom in on the runners, the gap gets even more concerning. Marathoners planned roughly 25.9 g/hour but only took in 21.7 g/hour. Not only is that a large discrepancy—it’s also well below mainstream race-day guidelines.
How far off are we, really?
Most sports-nutrition research suggests 30–60 g of carbohydrate per hour for events lasting 1–2.5 hours, and up to about 90 g/hour for longer efforts. Those marathoners averaging ~22 g/hour are sitting below the bottom of the recommended range.
The study also found that better sleep and lower pre-race “cognitive anxiety” (the worry spiral in your head) were linked with higher real-world carb intake. In other words, a calmer, better-rested athlete tends to fuel as they intended to more naturally.
So what does “enough” look like?
Once you’re past the 60–90 minute mark, “winging it” with one gel and a few sips of water usually lands you in that under-fuelled zone. Think in terms of a steady drip instead, aiming for roughly a gel or equivalent every 20–30 minutes.
That might look like a gel plus some sports drink over the hour, a banana spread out across the hour with a few gummies or a bottle of sports drink plus a small bar or a couple of electrolyte chews. The exact combo doesn’t matter as much as the total. Start with a clear, calculated plan, and follow it.
Don’t ignore the pre-race plate
Race-day fuelling also starts well before you hit the ground running. A carb‑focused meal two to three hours beforehand, like toast or a bagel with jam or oatmeal with banana and honey, sets you up so the stuff you take in during the race is topping up your fuel stores, not desperately trying to grind them into gear.
