How to fuel, when, and how much, matched to your distance and your level. Grounded in sports nutrition research, not guesswork.
Every piece of race nutrition, whatever the distance, comes down to three things: carbohydrate, fluid, and sodium. Get too little of any of them and performance suffers. Get too much and you risk gastric distress, which hurts performance just as badly. Everything below is about finding the right amount of each for your distance and your body, not chasing a perfect formula that doesn't exist.
Those are starting ranges, not fixed targets. Body size, sweat rate, pace, and heat all shift where you land in each range, which is exactly why the sections below are broken out by distance and by experience level rather than given as one-size-fits-all numbers.
Here's the honest truth: for a 5K or 10K, on-course fuelling is close to irrelevant. You'll be finished in well under 60 minutes even at a moderate pace, and your body's glycogen stores comfortably cover an effort that short. The nutrition question for these distances isn't about what you eat during the race, it's about what you've eaten in the days and hours before it.
This is where fuelling becomes a real decision rather than an afterthought. Most runners finish a half marathon somewhere between 90 minutes and 2.5 hours, which sits right at the edge of where glycogen stores alone start to run short. Whether you need on-course fuel depends mostly on your finishing time.
Finishing under about 75-90 minutes: fuel is optional, hydration matters more. Finishing beyond 90 minutes: plan on 30-60g of carbohydrate per hour from the second half of the race onward.
The marathon is long enough that nutrition genuinely determines how the last 10K feels. Glycogen stores typically run low somewhere between 90 minutes and 2 hours of steady running, well before most finishers cross the line. Under-fuel and you'll know exactly when: the wall, right on schedule.
The baseline recommendation, drawn from sports science bodies like the American College of Sports Medicine, is 60-90g of carbohydrate per hour for efforts over 90 minutes. That's based on the body's ability to absorb roughly 1g of carbohydrate per minute from the gut; with training and a mix of carbohydrate sources (glucose plus fructose, which use separate absorption pathways), that ceiling can rise toward 84g/hour or higher.
The same rule applies whether you're racing a 5K or a marathon: your last meal needs to be digested, not sitting heavy in your stomach, by the time the gun goes. Meal size should shrink the closer you get to race time.
| Time before race | Carbohydrate target | What that looks like |
|---|---|---|
| 3 hours | ~1.5g per kg of body weight | A full meal: oatmeal with fruit, a bagel with jam, pasta with a light sauce |
| 2 hours | ~1g per kg of body weight | Something smaller and simpler: toast, a banana, a small bowl of cereal |
| Under 1 hour | Small and liquid-leaning | A gel or sports drink if needed, nothing that requires real digestion |
Keep fat, protein, and fibre low in this meal. All three slow digestion, which is useful when you want to feel full for hours but works directly against you when you're about to put your gut under load. Save the fibre-rich, high-protein meals for other times of day.
Forget the old depletion-then-gorge protocol. Modern carb-loading is simpler: in the 1-3 days before a marathon, shift your diet toward roughly 8-10g of carbohydrate per kg of body weight per day, while training volume drops as part of your taper. You don't need to force-feed pasta at every meal, you need consistent, carb-forward eating while your legs are doing less work to burn through it.
Don't dramatically increase fibre intake in the 24-48 hours before the race while carb-loading. A large pasta dinner heavy in whole grains and vegetables the night before is a common cause of race-morning GI issues. Refined carbohydrates (white rice, white bread, ripe bananas) sit easier.
Sweat rate and sweat sodium concentration vary enormously between individuals, two runners standing next to each other in identical conditions can lose very different amounts of both. That's why generic hydration advice ("drink 500ml an hour") is a starting point at best.
The simplest way to check whether you're in the right range: weigh yourself before and after a long training run in similar conditions to race day. Losing more than 2% of body weight signals you needed more fluid; losing almost nothing, or gaining weight, signals you drank too much and are at some risk of diluting sodium levels (hyponatremia), which is more dangerous than mild dehydration.
Post-race recovery nutrition is one of the most oversold ideas in sports nutrition. You don't need a recovery shake within a mythical 20-minute window for it to "count." What actually matters:
This guide draws on sports nutrition research and coaching methodology from Jason Koop's Training Essentials for Ultrarunning and the Research Essentials for Ultrarunning series, cross-referenced against American College of Sports Medicine guidance. It's written for general education; individual needs vary, and athletes with specific medical conditions should consult a qualified professional.
Generic guidance gets you most of the way there. A coach who knows your history, your sweat rate, and your goal race closes the gap.
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