Few things ruin a run faster than getting your pre-run nutrition wrong. Eat too much and you'll feel sluggish, heavy, or worse - you'll experience that dreaded runner's stomach. Eat nothing and you might bonk halfway through, legs turning to jelly as your glycogen stores empty.
The good news: pre-run fuelling isn't complicated once you understand a few principles. And what works for a morning jog is different from what works before a marathon - this guide covers all scenarios.
The Science of Running Fuel
Your body stores roughly 2,000 calories of glycogen in muscles and liver - enough for approximately 90-120 minutes of running. That at moderate intensity (~60% VO2max), you'll use about 40-50% of your muscle glycogen in the first hour alone. Fat can't be converted to energy fast enough for running pace.
Aim for eating a meal rich in complex carbohydrates and protein 2-3 hours before exercise. The goal: arrive with topped-up glycogen stores without blood diverted to digestion when you need it in your legs.
Timing Your Pre-Run Fuel
Different Runs, Different Needs
🏃 Easy Run (Under 60 Minutes)
For shorter, steady-paced runs, your existing glycogen stores are usually enough. You don't need to eat specifically for the run if you've eaten normally that day.
⚡ Tempo or Interval Training
Higher intensity depletes glycogen faster. You'll want some fuel on board, but not so much it weighs you down during hard efforts.
🌄 Long Run (90+ Minutes)
Extended runs will deplete your ~2,000 calorie glycogen stores. Research supports consuming 30-60g carbohydrates per hour during runs over 60-90 minutes to maintain performance.
🌅 Early Morning Run
Most people can run for up to an hour fasted with no issues - you have enough stored glycogen from the previous day. For longer runs, you'll need something.
Best Pre-Run Foods
2-4 Hours Before (Full Meals)
30-60 Minutes Before (Quick Snacks)
What to Avoid Before Running
- High-fat foods: Slow digestion, heavy feeling, potential stomach issues
- High-fibre foods: The last thing you want mid-run is urgent toilet needs
- Spicy foods: Heartburn and reflux are no fun when running
- Large protein portions: Save the steak for after
- Unfamiliar foods: Never try something new before a run - stick to what you know works
- Too much food: Aim for satisfied, not full
Hydration: The Research
Studies show that just 2% body weight loss from dehydration impairs endurance performance by approximately 10%. For runs under an hour, hydration is actually more critical than food - you have sufficient glycogen stores, but dehydration happens fast.
- 2-3 hours before: Drink 400-600ml (the IOC recommends being well-hydrated with urine "pale yellow")
- 20 minutes before: Another 200-300ml, then stop to avoid sloshing
- During runs over 60 mins: Aim for 6-12oz (180-360ml) every 15-20 minutes
- Check your urine: Pale yellow = hydrated; dark = drink more
The Toilet Test
A good rule: aim to have a bowel movement before your run, especially for longer distances. Many runners have a pre-run routine (coffee helps) to ensure they're "empty" before heading out. Nothing ruins a run like needing to find a bush.
Running on Empty: What the Research Says
"Train low" strategies (training with low glycogen) show limited utility for enhancing performance. There's no evidence that low-carb training enhances outcomes compared to adequate carbohydrate intake.
Fasted running is fine for easy runs under an hour - you have sufficient glycogen stores. But for longer or intense runs, research consistently shows better performance with proper fuelling. The fat-adaptation theory hasn't delivered the promised benefits for most runners.
Evidence-Based Summary
Research supports: carb-focused meal 2-3 hours before (1-2g carbs/kg), or simple snack 30-60 mins before. For runs over 90 mins, consume 30-60g carbs/hour during. Stay hydrated (2% dehydration hurts performance). The golden rule: never try new foods on race day - practice your nutrition in training.
Training for a Race? See Our Distance-Specific Guides
After your run, recovery nutrition matters too. See our guide on what to eat after running.
← Back to Running & Races
