Should You Eat a Lot of Carbs Before a Run? The Essential Fueling Guide

October 20, 2025 •

4 min read

For endurance athletes participating in events longer than 90 minutes, consuming a high-carbohydrate diet has been shown to improve performance by up to 3%. But the answer to should you eat a lot of carbs before a run? is nuanced and depends on the duration and intensity of your training.

Quick Summary

This guide examines the appropriate carbohydrate intake before a run, differentiating strategies for short and long distances. It details the best timing for meals and snacks, compares simple versus complex carbs, and explains how to prevent gastrointestinal issues while fueling for optimal performance.

Key Points

Distance Determines Intake: A large carb meal is only necessary before long, intense runs. For shorter runs (under 60 minutes), your body's stored glycogen is often sufficient.
Strategic Timing is Key: Eat a full, carb-heavy meal 2-4 hours before a long run, and stick to a small, easily digestible snack (like a banana) within 30-60 minutes of starting.
Use the Right Carbs at the Right Time: Utilize complex carbs (whole grains, oats) for sustained energy in daily meals, and simple carbs (fruits, gels) for a quick, immediate fuel source.
Practice to Prevent Problems: Always test new fueling strategies and foods during training, not on race day, to minimize the risk of gastrointestinal distress like bloating or cramping.
Don't Overload Unnecessarily: Excessively carb-loading for a short or moderate run is unnecessary and can cause discomfort. Match your fuel intake to the demands of your workout.
Hydration is Critical: Adequate fluid and electrolyte intake supports carbohydrate absorption and helps prevent dehydration, which negatively impacts performance.

The Importance of Carbohydrates for Runners

Carbohydrates are the body's preferred source of energy, especially during moderate to high-intensity exercise like running. When you consume carbohydrates, your body converts them into glucose, which is then either used for immediate energy or stored as glycogen in the muscles and liver. A runner's performance is directly linked to these glycogen stores. When these stores are depleted, a runner may experience fatigue, often referred to as 'hitting the wall'. Adequate carb intake is essential for maintaining sufficient energy levels to sustain your running session and promote faster recovery.

Fueling Strategy Based on Run Length

The amount of carbohydrates you need before a run is not a one-size-fits-all solution; it depends heavily on the length and intensity of your workout.

Short Runs (under 60 minutes)

For an easy-paced run lasting an hour or less, your body's existing glycogen stores are typically sufficient. Many runners can perform a short workout without eating beforehand, especially if they are well-fueled from previous meals. However, if you run first thing in the morning or feel low on energy, a small, easily digestible snack can provide a quick boost without causing stomach upset. A snack 30 to 60 minutes prior is generally enough to top off liver glycogen stores that may have been depleted overnight.

Long Runs (over 90 minutes)

This is where consuming more carbohydrates becomes critical. For long runs or endurance races, your body requires more fuel to prevent glycogen depletion. Endurance athletes, such as marathoners, often employ a strategy called 'carb-loading' in the days leading up to the event. This involves significantly increasing carbohydrate intake to maximize muscle glycogen stores, which can delay fatigue and help you finish strong. For example, a sports dietitian might recommend 10–12 grams of carbs per kilogram of body weight per day in the 36-48 hours before a marathon. Even during long training runs, practicing fueling mid-run is crucial to teach your body to tolerate and absorb the carbs it needs.

The Best Timing and Types of Carbohydrates

Timing Your Pre-Run Meal

2-4 Hours Before: A substantial, carb-focused meal is ideal for providing sustained energy. This meal should be moderate in protein and low in fat and fiber to aid digestion. Examples include oatmeal with berries, a bagel with peanut butter, or a turkey sandwich on whole-wheat bread.
30-60 Minutes Before: For those short on time, a quick snack focusing on easily digestible simple carbohydrates is best. This provides a rapid energy source to boost blood glucose without weighing you down. Think bananas, applesauce, or a sports gel.

Simple vs. Complex Carbs

Not all carbs are created equal. The type you choose depends on when you plan to eat.

Complex Carbohydrates: Found in whole grains, oats, and starchy vegetables, these digest slowly and provide a steady release of energy. They are best for the main meals consumed hours before a long run. A runner's diet should primarily consist of these nutrient-dense options.
Simple Carbohydrates: Found in fruits, sports drinks, and energy gels, these are digested quickly, offering a fast energy boost. They are perfect for a snack right before a run or for mid-run fueling.

Comparison: Short vs. Long Run Fueling


Aspect	Short Run (<60 minutes)	Long Run (>90 minutes)
Pre-Run Meal Timing	Can run on existing glycogen; if eating, small snack 30-60 min before.	Larger meal 2-4 hours before; carb-loading days before a race.
Carb Type	Simple, fast-digesting carbs for a quick boost (e.g., banana).	Complex carbs for sustained energy in main meals; simple carbs for immediate fuel.
Carb Quantity	Minimal (15-40g); often not necessary.	High; up to 10-12g/kg BW/day during carb-loading.
Mid-Run Fueling	Not necessary.	Essential; 30-60g carbs per hour from gels, chews, etc..
Post-Run Focus	Refuel and rehydrate for general recovery.	Restore depleted glycogen and repair muscle with carbs and protein.

Avoiding Over-fueling and Digestive Distress

Eating too many carbohydrates or the wrong type of foods too close to your run can lead to discomfort, a feeling of heaviness, bloating, or cramping. This is especially true for fibrous foods, which take longer to digest.

Tips to minimize risk:

Practice your fueling strategy during training runs, not on race day. This helps your gut become accustomed to processing food while you run.
Reduce fiber and fat intake in the final 24 hours before a race or long run to aid digestion.
Listen to your body. Everyone's tolerance is different. Start with smaller amounts of food and gradually increase as needed.

Conclusion: Finding the Right Balance

Ultimately, the question of whether you should eat a lot of carbs before a run depends on the specific demands of your workout. For short, easy runs, a small snack is plenty or even unnecessary, as your body’s existing fuel is adequate. However, for long distances and high-intensity efforts, a high-carbohydrate strategy involving proper timing and selection of carb types is crucial for optimizing performance and avoiding the dreaded energy crash. By understanding the difference between simple and complex carbs, and practicing your fueling strategy during training, you can ensure your body is always ready to perform at its best. Consulting a sports dietitian can provide personalized guidance, but consistent experimentation during training is the best way to determine what works for you.

For more in-depth nutritional information for runners, visit Mayo Clinic Health System.

Frequently Asked Questions

For easy, short runs under an hour, running on an empty stomach is generally fine as your body has enough stored glycogen. However, for longer or more intense runs, some fuel is recommended to optimize performance and prevent fatigue.

Complex carbohydrates (e.g., oats, whole grains) provide a slow and sustained energy release, making them ideal for the main meals consumed hours before a long run. Simple carbohydrates (e.g., fruit, gels) offer a quick energy boost, best for snacks right before or during a run.

A small, easily digestible snack like a banana, a piece of toast with jam, or a handful of pretzels is ideal if you need a quick energy top-up 30-60 minutes beforehand.

Yes, overeating, especially high-fiber or high-fat foods, too close to a run can lead to gastrointestinal distress, including bloating, cramping, and 'runner's trots'.

For a long run or race, aim to eat your main carb-focused meal 2 to 4 hours beforehand to allow for proper digestion and maximize glycogen storage without causing discomfort.

Carb-loading typically involves increasing carbohydrate intake to 10-12 grams per kilogram of body weight per day in the 36-48 hours leading up to an endurance event. It's best to reduce fiber and fat intake during this period.

Yes, for runs lasting longer than 90 minutes, it's recommended to consume 30-60 grams of simple carbohydrates per hour, often using gels, chews, or sports drinks, to maintain energy levels.