How long before a run should you carb up?

December 4, 2025 •

4 min read

For endurance events over 90 minutes, carbohydrate loading can improve performance by up to 2-3%. Knowing how long before a run should you carb up is essential to maximize energy stores and avoid mid-run fatigue, often called 'hitting the wall'.

Quick Summary

This guide outlines the optimal timing and type of carbohydrate intake for runners based on run duration and intensity. It covers strategies for short runs, medium runs, long training sessions, and effective multi-day carb-loading protocols for races, emphasizing the importance of individualized fueling plans.

Key Points

Timing by Run Length: For short runs (<60 min), a quick, simple carb snack 30-60 minutes prior is fine; for longer runs, a meal 1-3 hours before is better.
Endurance Events: Begin carb-loading 1-3 days before an endurance race to maximize glycogen stores by consuming 8-12g of carbs per kg of body weight.
Familiar Foods First: Always stick to familiar, easy-to-digest carb sources during the carb-loading phase to avoid race day stomach issues.
Pre-Race Dinner: Eat a moderate, carb-heavy dinner on the early side the night before to ensure proper digestion before bed.
Race Day Breakfast: Have your final top-up meal 2-4 hours before the start line, focusing on easily digestible, simple carbohydrates.
Trial and Error: Experiment with different fueling strategies during long training runs to discover what works best for your body before race day.

Understanding Glycogen: The Runner's Fuel Tank

Before diving into the timing, it's crucial to understand what carbohydrates do for a runner. The body converts carbohydrates into glucose, which is then stored in the muscles and liver as glycogen. This stored glycogen is the primary and most readily available fuel source for high-intensity and prolonged exercise. During a long run, your body uses these glycogen stores, and once they are depleted, fatigue sets in. The goal of 'carbing up' is to top off these fuel tanks to their maximum capacity, ensuring you have enough energy to perform at your best for the duration of your run or race.

Timing Your Carb Intake by Run Duration

The amount and timing of your carbohydrate intake should be proportional to the length and intensity of your run. A 5K does not require the same fueling strategy as a marathon, and what you eat 30 minutes before a run differs significantly from a meal consumed two hours prior.

For Short Runs (<60 minutes)

For shorter, easy-to-moderate runs lasting less than an hour, your existing glycogen stores are usually sufficient. A full meal beforehand is generally unnecessary and can lead to stomach upset.

30-60 minutes before: Opt for a small, easily digestible snack of simple carbohydrates. Examples include a banana, a small handful of pretzels, or half a sports energy bar. The goal is to provide a quick energy boost without overburdening your digestive system.

For Medium Runs (60-90 minutes)

As your run time approaches the 60-90 minute mark, your body will start tapping into its glycogen reserves more significantly. Proper pre-run fueling helps spare these stores for when you really need them.

1-2 hours before: A light snack or small meal containing a mix of simple and complex carbohydrates is ideal. The simple carbs provide immediate energy, while the complex carbs offer a more sustained release throughout your run. Examples include a bowl of oatmeal, a bagel with a thin layer of jam, or toast with a small amount of nut butter.

For Long Runs (>90 minutes)

For long runs and endurance events, a more strategic approach is needed, involving multi-day carb-loading to maximize muscle glycogen storage. Practicing this strategy during training is essential to find what works best for you.

1-3 days before: This is the carb-loading phase. Gradually increase your carbohydrate intake while tapering your training volume. The Mayo Clinic recommends consuming 8 to 12 grams of carbohydrates per kilogram of body weight per day in the days leading up to an endurance race. Spread your carb intake across smaller, frequent meals and snacks to avoid feeling uncomfortably full.

The Art of Carb-Loading for Endurance Events

True carb-loading is not about a single massive meal the night before, but a strategic increase in carbohydrate consumption over a few days.

Best Practices for Carb-Loading

Choose Familiar Foods: Stick to foods that you know your body tolerates well to avoid gastrointestinal issues on race day.
Prioritize Complex Carbs: Focus on complex carbs like pasta, rice, potatoes, and bread, which are digested more slowly and provide a steady energy release.
Limit Fat and Fiber: High-fat and high-fiber foods can slow digestion and cause discomfort during your run. Opt for simpler versions of your favorite carb sources, like white rice instead of brown or refined pasta.
Stay Hydrated: Water is critical for storing glycogen. Drink plenty of fluids alongside your carb-rich meals.

The Night Before the Race

Keep your dinner simple and moderate in size. A large, heavy meal can disrupt sleep and digestion. A moderate portion of plain pasta with a simple sauce or a baked potato is a classic choice. Eat on the early side to allow for adequate digestion time.

The Race Day Breakfast

This meal is your final top-up of glycogen stores. Eat it 2 to 4 hours before the race starts. It should be carb-focused, low in fiber and fat, and something you have practiced with during training. Examples include a bagel with jam, oatmeal, or a banana.

Complex vs. Simple Carbs: The Glycemic Index

The glycemic index (GI) measures how quickly a carbohydrate-containing food raises blood sugar levels. Understanding the difference helps tailor your fueling strategy.


Feature	Complex Carbs (Low GI)	Simple Carbs (High GI)
Digestion Speed	Slower	Faster
Energy Release	Sustained, steady	Quick burst, followed by potential crash
Best Used	For the multi-day carb-load and for fueling 2+ hours pre-run.	For snacks 30-60 minutes pre-run or during the run.
Examples	Oatmeal, sweet potatoes, whole grains, lentils, brown rice.	Bananas, energy gels, sports drinks, pretzels, white rice.
Fiber Content	Generally higher	Generally lower

Conclusion: Practice Makes Perfect

Ultimately, the question of how long before a run should you carb up depends on the individual and the specifics of their run. The strategies outlined here are excellent starting points, but the best approach is to experiment with different foods and timings during your training. Use your longest training runs as an opportunity to test your carb-loading and pre-run breakfast strategies. Listen to your body and make adjustments based on how you feel. By practicing your fueling plan in advance, you'll be confident and well-prepared on race day, ensuring your hard training pays off with a strong, fueled performance. For more detailed training plans and nutrition advice, consider checking resources like Runner's World.

Frequently Asked Questions

Carb-loading is generally not necessary for runs or races lasting less than 90 minutes. A balanced daily diet and a small, simple carb snack 30-60 minutes beforehand should suffice.

Effective carb-loading foods include easy-to-digest sources like pasta, rice, oats, sweet potatoes, bananas, and bagels. It's best to reduce high-fiber intake during this period.

No, carb-loading is a multi-day process, not a single meal. A large meal the night before can cause bloating and discomfort; instead, spread increased carb intake over 1-3 days.

For race day, aim for a meal of simple, low-fiber carbs 2-4 hours before the start. Good options include a bagel with jam, oatmeal, or bananas, ensuring you use foods tested in training.

A small amount of temporary weight gain is normal due to increased glycogen and associated water retention. However, significant bloating can be a sign of too much fiber or eating too quickly. Spread your intake over smaller, more frequent meals to minimize this.

An energy gel or easily digestible simple carb snack can be consumed 30-60 minutes before a race or long run to top off your energy stores. For longer events, additional fueling will be needed during the run.

No, you don't need to eliminate fat and protein entirely. You should, however, shift the balance of your meals to be predominantly carbohydrate-heavy while keeping fat and fiber low to optimize digestion.