A Runner's Guide: How much carbs to eat before a long run?

October 18, 2025 •

4 min read

According to sports dietitians, carbohydrates are the body's preferred fuel source for endurance running, making it crucial to know exactly how much carbs to eat before a long run. Getting your pre-run fueling right can make the difference between a successful outing and hitting the wall prematurely.

Quick Summary

Fueling for a long run is individualized but involves consuming easily digestible carbs 2-4 hours prior, with a smaller top-up snack closer to the start. The right amount depends on body weight and timing, so experimenting during training is key to find your optimal strategy.

Key Points

Timing is Crucial: A main carb-rich meal 2–4 hours before a long run is ideal for replenishing glycogen stores, while a smaller, easily digestible snack can be consumed 30–60 minutes prior for a final top-up.
Personalize Your Intake: A starting recommendation for a pre-run meal is 1–4g of carbohydrates per kilogram of body weight, but individual needs vary, so test your strategy during training.
Prioritize Simple Carbs Pre-Run: Focus on easily digestible, low-fiber carbs like white bread, bagels, bananas, or energy gels in the hours before a run to minimize GI distress.
Avoid High Fiber and Fat: Limit foods high in fiber and fat immediately before a run, as they slow digestion and can cause stomach issues during exercise.
Practice Makes Perfect: Never try a new fueling strategy on race day. Use your training runs to practice and refine what works best for your body.
Carb-Load for Races: For marathons and similar long events, consider a carb-loading phase 1-2 days prior, consuming 8–12g of carbs per kg of body weight to maximize glycogen stores.

Why Carbohydrates Are Non-Negotiable for Long Runs

Carbohydrates are a runner's primary and most efficient energy source, stored in the muscles and liver as glycogen. During prolonged, high-intensity exercise like a long run, your body relies heavily on these glycogen stores to power your muscles and sustain your effort. Starting a long run with depleted glycogen reserves can lead to premature fatigue, reduced performance, and the dreaded 'bonk'. Therefore, strategically timed and portioned carbohydrate intake is essential for maximizing performance and endurance.

The Two-Pronged Pre-Run Fueling Approach

Fueling before a long run is a two-step process involving a main meal several hours beforehand and a smaller snack closer to the start time.

The Main Meal (2–4 hours before): This is your opportunity to top off your muscle and liver glycogen stores. The recommendation is to consume 1–4 grams of carbohydrates per kilogram of body weight during this window. This meal should be primarily carbohydrate-based, low in fat, and low in fiber to ensure quick digestion and absorption, minimizing the risk of gastrointestinal (GI) issues during your run.
The Top-Up Snack (30–60 minutes before): For runners who prefer a lighter start or need a quick energy boost, a small, easily digestible snack is perfect. This should provide around 25–50 grams of simple carbohydrates to elevate blood glucose levels without causing stomach discomfort.

Calculating Your Individual Needs

To determine your personalized carbohydrate needs, you first need to know your body weight in kilograms. (To convert, divide your weight in pounds by 2.2).

Example: For a 150-pound (68 kg) runner:

Main meal (2–4 hours prior): Aim for 136–272g of carbs. This could look like a large bowl of oatmeal with banana and honey.
Top-up snack (30–60 minutes prior): Aim for 25–50g of carbs. This could be a banana or a handful of pretzels.

Choosing the Right Carbs: Simple vs. Complex

Not all carbohydrates are created equal, and the timing of your intake should influence your choices. While complex carbs (like whole grains) are excellent for daily energy, simple, easily digestible carbs are preferred in the hours immediately preceding a long run.

Best Carbs to Eat Before a Run:

Bagels: A simple bagel with a little jam is a quick-digesting option.
White rice/pasta: These have less fiber than their whole-grain counterparts, making them easier to digest before intense exercise.
Bananas: Packed with easily digestible carbs and potassium, bananas are a classic pre-run snack.
Oatmeal: A bowl of porridge with banana and honey provides sustained energy and is gentle on the stomach.
Energy Gels/Chews: These offer a concentrated source of simple carbs for a quick boost.
Pretzels: Salty and carbohydrate-rich, pretzels are a great top-up snack option.

Comparison: Pre-Run Meal vs. Pre-Run Snack


Feature	Pre-Run Meal (2–4 hours prior)	Pre-Run Snack (30–60 minutes prior)
Purpose	To fully stock muscle and liver glycogen stores for maximum endurance.	To top up blood glucose levels and provide a quick energy boost.
Carb Type	Mostly simple, low-fiber carbs (e.g., white pasta, bagels).	Simple, fast-digesting carbs (e.g., bananas, energy gels).
Amount	1–4 grams of carbs per kilogram of body weight.	25–50 grams of carbohydrates.
Ideal Foods	Oatmeal with fruit, white rice with a light sauce, bagel with jam.	Banana, pretzels, energy gel, small fruit pouch.
Avoid	High-fiber, high-fat foods, spicy meals.	Anything new, large quantities, high-fat/fiber.

Additional Fueling Tips for Long-Distance Runners

Carb-Loading (2-3 days before): For races longer than 90 minutes, consider a carb-loading phase involving 8–12 grams of carbohydrates per kilogram of body weight per day while tapering training. Focus on low-fiber carbs to prevent GI issues.
Fuel During the Run: For runs longer than 60–75 minutes, plan to take in additional carbs during the run itself. Aim for 30–60g of carbs per hour, using gels, chews, or sports drinks.
Hydrate Consistently: Don't forget proper hydration. Drink water or electrolyte drinks consistently before and during your run to replace lost fluids.
Listen to Your Body: Every runner's digestive system is different. What works for one person may cause problems for another. Use your training runs as an opportunity to experiment with different fueling strategies and find what feels best for you.

Conclusion: Fuel Smart, Run Strong

Knowing how much carbs to eat before a long run is a cornerstone of effective endurance training and race preparation. By understanding the timing, type, and quantity of carbohydrates needed, runners can optimize their energy stores and prevent performance-limiting fatigue. The ideal strategy involves a carb-rich main meal hours before, followed by a smaller, simple carb snack closer to the start, all of which should be practiced and fine-tuned during training. Experimentation is crucial, and listening to your body's response will ultimately lead to a more successful and comfortable long-distance running experience. For more expert advice, check out the resources from the Mayo Clinic Health System.

Frequently Asked Questions

A pre-run meal should be high in easily digestible carbs (1–4g per kg of body weight), moderate in protein, and low in fat and fiber. Examples include a bagel with jam or oatmeal with fruit and honey.

Energy gels, chews, or sports drinks are not necessary for all long runs, but they are highly recommended for runs longer than 60–75 minutes to provide a quick, concentrated source of carbs during exercise.

For runs longer than 60 minutes, running on an empty stomach is not recommended. You start with partially depleted glycogen stores, which can lead to early fatigue and poorer performance.

Opt for a small, easily digestible carb snack like a banana or pretzels 30–60 minutes before your run. Focus on a carb-rich meal the evening before to stock your glycogen stores overnight.

Carb-loading is a strategy for marathons or very long races where you consume high amounts of carbohydrates (8–12g/kg body weight) for 1–2 days before the event to maximize your glycogen reserves.

Good options for quick, pre-run energy include bananas, pretzels, white toast with jam, rice cakes, and energy gels. These are low in fiber and digest quickly.

High-fiber and high-fat foods slow down digestion, which can cause bloating, cramps, and other gastrointestinal distress during exercise, especially during intense running.