Carb-loading isn’t just about eating more, it’s about fueling smarter. Get it right, and you’ll feel the difference when it matters most: on race day. This article, written by Amy from The Running Dietitian, is here to guide you.
What Actually Is Carb-Loading?
Carb-loading is the process of increasing carbohydrate intake in the 1-3 days before a race to help your muscles maximize glycogen stores, your body’s stored energy. This is especially important for endurance events like a half or full marathon. Research shows that carb-loading can improve performance by 2–3% and help delay fatigue.
The Science Behind Carb-Loading
Your body stores carbohydrates as glycogen in the muscles and liver– think of it like your fuel tank. While running, your body relies heavily on glycogen because it can be broken down quickly to power your muscles. The challenge is that these stores are limited, with most runners holding enough glycogen to fuel about 90–120 minutes of running.
Carb-loading helps maximize these stores in the days leading up to a race, giving you a larger reserve of energy to pull from on race day. However, carb-loading alone is not enough. To avoid hitting the wall, you still need to consume carbohydrates during the race to keep supplying your body with fuel and prevent your tank from running empty.
Outdated carb-loading methods once recommended a depletion phase where athletes significantly reduce carbohydrate intake before loading, but current research shows this is unnecessary.
Who Needs To Carb Load?
Carb-loading is most beneficial for races lasting 90 minutes or longer. For most runners, this includes half marathons, marathons, and ultramarathons. During shorter races, glycogen stores are typically sufficient without needing a dedicated carb- loading strategy.
Carb-Loading for Races vs Training Sessions
Carb-loading is most commonly associated with races, but it can also be useful during key training sessions that you complete in the biggest weeks of your plan.
As training volume increases, your daily carbohydrate intake should increase as well to support both performance and recovery.
Runners may benefit from increasing carbohydrates the day before runs lasting 2 hours or longer, helping ensure glycogen stores are adequately topped off.
Practicing a carb-load during training also allows you to identify which foods work well for your body and which might cause gastrointestinal discomfort.
Incorporating a practice carb-load during peak training week serves two purposes: it helps you dial in your race week fueling strategy and finalize your plan, while also providing the extra carbohydrates needed to support your highest mileage and longest training runs.
When to Start Carb-Loading Before a Race?
Carb-loading usually begins one to three days before race day. The length of the carb-load often depends on race distance and the carbohydrate target a runner is trying to reach.
Our Race-Day Nutrition Checklist guides you on what to prepare for and what to pack.
Some runners prefer a two-day carb-load with a higher daily carbohydrate intake, while others find it easier to spread their intake over three days at a slightly lower amount. Both approaches can be effective when total carbohydrate intake is sufficient.
How Much Do You Need?
During carb-loading, aim for 8–12 grams of carbohydrates per kilogram of body weight.
For a half-marathon, this carb-load is typically done 1–2 days before the race, and for a full marathon, 2–3 days prior.
Consuming more than 800 g of carbohydrates per day can be challenging, so in those cases, focus on the lower end of the recommended range.
Body Weight (kg) | Body Weight (lb) | Low Range (8g/kg or 3.6g/lb) | High Range (12g/kg or 5.5g/lb) |
50 | 110 | 400 | 600 |
57 | 125 | 450 | 686 |
64 | 140 | 504 | 770 |
70 | 155 | 558 | 852 |
77 | 170 | 612 | 935 |
84 | 185 | 666 | 1017 |
91 | 200 | 720 | 1100 |
102 | 225 | 810 | 1237 |
What To Eat Whilst Carb-Loading
During the carb-loading phase, it’s best to focus on familiar, easy-to-digest foods.
Fat intake is often reduced slightly during a carb-loadbecause high-fat meals can slow digestion and increase the risk of gastrointestinal discomfort during a race. Similarly, fiber intake is usually lowered to minimize digestive issues.
This might mean choosing white rice instead of quinoa or white bread instead of whole wheat bread. Meals should be centered around carbohydrate-rich foods such as rice, pasta, potatoes, or bread, so that carbohydrates form the foundation of each meal.
Liquid Carbohydrates
Liquids can also help runners meet their carbohydrate needs. Beverages such as orange juice, sports drinks like Gatorade, smoothies, and chocolate milk provide carbohydrates that are often easier to consume when appetite begins to decrease during a carb-load.
Common Carb-Loading Mistakes
Not drinking enough fluids: Hydration needs increase during a carb-load, both because carbohydrate intake is higher and because glycogen storage requires water.
Focusing too much on body weight: It is normal for body weight to increase slightly because glycogen is stored with water in the muscles. This temporary weight gain is a normal part of the carb-loading process.
Consuming too many carbohydrates at one meal instead of spreading them: Distributing carbohydrates across meals and snacks can make the process feel much more manageable.
Not allowing enough time: Many runners assume that dinner the night before the race should be the largest meal of the carb-load. In reality, lunch the day before the race gives the body more time to digest before race morning, particularly if your race is early.
Key Takeaways
Carb-loading helps runners maximize glycogen stores before longer races. Glycogen is the body’s primary fuel source for running, but these stores are limited. By strategically increasing carbohydrate intake in the days leading up to a race, runners can increase their fuel reserves and delay fatigue.
Carb-loading works best when it is combined with consistent fueling habits during training and a well-planned race-day fueling strategy. It is not simply about eating more carbohydrates the night before a race, but about preparing the body with the fuel it needs to perform well on race day.