| What it is | Eating extra carbs before a race |
| Goal | Maximize muscle/liver glycogen |
| Benefit | Delays glycogen depletion (the bonk) |
| Best for | Events ~90+ minutes |
Carb loading (carbohydrate loading) is the practice of eating extra carbohydrates in the days before an endurance event to maximize the glycogen stored in your muscles and liver — your primary fuel for prolonged exercise. By topping off these stores, runners delay glycogen depletion and the resulting ‘bonk,’ which is most beneficial for events lasting roughly 90 minutes or longer.
Fuel up
Done during the taper to stave off the bonk; during the race you keep fueling with a gel.
Frequently asked questions
What is carb loading?
Carb loading is increasing your carbohydrate intake in the days leading up to an endurance event to maximize the glycogen (stored carbohydrate) in your muscles and liver. Since glycogen is your body's main fuel for sustained hard effort, starting a race with full stores helps you go longer before running low and hitting the wall.
How do you carb load?
Typically you raise the proportion of carbohydrates in your diet for one to three days before the event (commonly cited around 8–12 grams of carbohydrate per kilogram of body weight per day for the final day or two), while reducing training during the taper so the glycogen accumulates. Choose familiar, easily digested carbs and avoid overeating fiber or fat.
Who benefits from carb loading?
It mainly helps in longer endurance events — roughly 90 minutes or more — where glycogen depletion limits performance, such as marathons and ultras. For short races it offers little benefit. During very long events, carb loading is combined with consuming carbohydrates (like gels) while running to keep fueling and avoid the bonk.
Sources
- Carbohydrate loading — American Council on Exercise
- Race nutrition — American Trail Running Association