Should I Eat Carbs Before a Run? Your Ultimate Fueling Guide

December 13, 2025 •

3 min read

Studies show that runners who consume adequate carbohydrates can improve their endurance and delay fatigue, especially during high-intensity or long-duration exercise. This guide breaks down the science behind fueling your body for your run.

Quick Summary

Carbohydrates are a runner's primary energy source, crucial for powering muscles during exercise. An optimal pre-run fueling strategy depends on the run's duration and intensity, focusing on timing and carbohydrate type.

Key Points

Duration is Key: The length and intensity of your run dictate your pre-fueling needs; shorter runs require less, while longer runs demand more strategic carb intake.
Timing is Everything: Eat a full meal 3-4 hours before, a snack 1-2 hours before, and a quick, small carb source 30-60 minutes prior for optimal digestion and energy.
Choose the Right Carbs: Prioritize complex carbohydrates for meals further from your run and simple, easily digestible carbs for snacks closer to the start time.
Avoid GI Distress: To prevent stomach issues, limit high-fat, high-fiber, and heavy protein foods right before running, and test new foods during training.
Practice 'Gut Training': For endurance events, gradually increase and practice your fueling strategy during training to teach your digestive system to tolerate a higher carbohydrate intake.
Carbs are Energy: Carbs are your body's primary fuel source, essential for replenishing glycogen stores and maintaining blood glucose for sustained performance.

The Science of Carbs and Running Performance

Carbohydrates are a runner's primary and most efficient energy source. They are broken down into glucose, used for immediate energy, or stored as glycogen in muscles and the liver. These glycogen stores are critical for moderate to high-intensity exercise.

The Glycogen Factor

During prolonged or intense runs, muscles deplete glycogen reserves, leading to fatigue or "hitting the wall". Eating carbs beforehand replenishes these stores for optimal performance and helps maintain stable blood sugar, preventing dizziness. The type and timing of carb intake should align with your training goals and run duration.

Fueling Strategy Based on Run Duration

Your fueling needs depend significantly on how long and how intensely you plan to run.

Short Runs (Under 60 minutes)

For easy runs under an hour, existing glycogen is usually enough. If you've eaten recently, you may not need extra fuel. If running on an empty stomach, a small, easily digestible snack can provide a quick boost without causing discomfort.

Recommended Snacks (30-60 minutes before):
- Half a banana
- Pretzels or crackers
- Small energy bar
- Sports drink sips

Longer or More Intense Runs (Over 60 minutes)

Longer or more intense runs require a strategic fueling plan to prevent glycogen depletion.

Large Meal (3-4 hours before): A meal high in complex carbs, moderate protein, and low in fat/fiber allows for thorough digestion and glycogen storage. Example: Oatmeal with fruit and nuts.
Smaller Meal (1-2 hours before): Focus on digestible carbs and some protein. Example: Bagel with peanut butter or a fruit smoothie.
Quick Snack (30-60 minutes before): Simple carbs for a fast energy boost. Example: Banana, energy gels, or sports chews.

Simple vs. Complex Carbohydrates for Runners

Carbohydrate types affect energy release.

Simple Carbohydrates: Quick digestion causes a blood sugar spike, ideal for immediate energy before or during a run. Examples: ripe bananas, pretzels, sports drinks.
Complex Carbohydrates: Slower digestion provides sustained energy, best for meals several hours before a run to build glycogen stores. Examples: oatmeal, whole-grain bread, pasta.

Comparison of Pre-Run Fueling Strategies


Run Duration	Timing Before Run	Carbohydrate Focus	Examples of Fuel
Under 60 min (easy)	Optional, 30-60 min before	Small, simple carbs	Banana, pretzels, sports drink
1-2 hours (moderate-intense)	1-2 hours before	Simple carbs + moderate protein	Smoothie, oatmeal with berries
Over 2 hours (long-distance)	3-4 hours before (main meal)	Complex carbs + protein	Pasta with a light sauce, rice bowl
	30-60 minutes before (top-up)	Simple carbs (gels, chews)	Energy gels, sports chews, dried fruit

What to Eat and What to Avoid

Avoiding certain foods can prevent digestive issues like "runner's trots". High-fiber, high-fat, and high-protein foods are slow to digest and can cause discomfort.

Foods to Prioritize:
- White rice or white pasta
- Bananas
- Oatmeal
- White bread or toast
- Pretzels
- Energy gels and sports drinks (for longer runs)
Foods to Limit or Avoid:
- Excessive fiber (e.g., bran muffins, beans)
- High-fat foods (e.g., fried foods)
- Heavy protein meals
- Spicy foods

Training Your Gut for High-Carb Intake

For races like marathons, practice increasing carbohydrate intake during training to help your digestive system adapt, minimizing race day issues.

Start Slowly: Begin with small amounts of carbs during longer runs.
Increase Gradually: Progressively raise carb intake over weeks to reach your race day target.
Experiment: Try different products (gels, chews) to find what works best.
Stay Hydrated: Drink water with gels and chews for absorption and hydration.

Conclusion: Your Fueling Depends on Your Run

Eating carbs before a run is beneficial, but the strategy should be tailored to your workout. Short runs may only need a small snack or a prior meal, while longer runs require strategic pre- and sometimes mid-run fueling to maintain performance. Focus on easily digestible carbs before your run, and experiment during training to find what suits your body best. Proper fueling helps ensure you perform optimally.

For more in-depth nutritional guidance, consider consulting an expert. Here's a link to learn more from the Hospital for Special Surgery on pre- and post-workout nutrition.

Frequently Asked Questions

For short, easy runs (under 60 minutes), your existing glycogen stores are often sufficient, so running on an empty stomach might be fine. However, for longer or more intense runs, it is best to eat beforehand to prevent fatigue and sustain performance.

For an early morning run, a small, easy-to-digest simple carbohydrate is best. A banana, a slice of white toast with honey, or a small handful of pretzels can provide a quick energy boost without upsetting your stomach.

The timing depends on the size of your meal. General guidelines suggest a large meal 3-4 hours before, a smaller meal 1-2 hours before, and a light snack 30-60 minutes before exercising.

Eating simple carbs too close to a run can cause a quick blood sugar spike followed by a drop. Choosing more complex carbs for meals further out and smaller, timely simple carb boosts closer to the run helps maintain stable blood sugar levels.

For marathons, a larger meal of complex carbohydrates (like pasta or rice) 3-4 hours before, followed by a small, simple carb snack closer to the start, is recommended to maximize glycogen stores. During the run, continue fueling with 30-60 grams of carbs per hour.

To prevent gastrointestinal issues, avoid high-fiber, high-fat, and heavy protein meals in the hours leading up to a run. Examples include fried foods, creamy sauces, and high-fiber cereals.

Practical examples include oatmeal with berries (1-2 hours before), a banana with peanut butter on toast (1 hour before), or a sports gel (30 minutes before). Experiment with different options to find what works for you.

Carb-loading, which involves increasing your carb intake in the days leading up to an event, helps maximize your muscle glycogen stores. This provides a deep energy reserve, allowing you to sustain effort for a longer period and delaying fatigue.