When it comes to carb loading, the pre-race pasta dinner and the marathon go hand-in-hand. It’s a long-running joke (pun intended) that if you’re gearing up for a marathon, you’re going to be eating lots of carbs the days leading up to your race.
As both a coach and a runner, I’ve learned that carb loading is more than just piling pasta on your plate the night before a race. In fact, trying to cram all your carbs into one pre-race meal can actually backfire—causing digestive issues, fatigue, and even inflammation when it matters most.
Over the years, I’ve seen (and made!) plenty of carb loading mistakes. That’s why I put together this guide—to help you understand what carb loading really is, how to do it right, and how to avoid the most common mistakes runners make when trying to fuel up for race day.
Let’s get you fueled up for peak performance.
Why Are Carbohydrates So Important For Runners?
Carbohydrates in the form of glycogen are your body’s preferred energy source for running. And for races lasting longer than 90 minutes, filling up these fuel stores is key to helping you go the distance.
How do you do this?
By eating carbs to maximize your liver and muscle glycogen stores. You need these carb stores because your body only has limited room for this fuel:
“With only 2,000 calories worth of energy stored from carbohydrates, our body will run out of fuel after approximately two hours.” explains exercise physiologist and world-champion triathlete Todd Buckingham.1Mary Free Bed Rehabilitation Hospital: Home. (n.d.). Mary Free Bed Rehabilitation Hospital. Retrieved January 9, 2024, from https://www.maryfreebed.com/
”By increasing the number of carbohydrates the body can store, we can run for a longer period of time without running out of energy”
Thus, carb loading involves gradually increasing your total carbohydrate intake prior to an athletic event so that you have excess glycogen in your liver for your muscles to tap into for endurance events and long-duration exercises.
“By eating more carbohydrates, you may be able to store more energy in your muscles giving you the stamina to make it through longer endurance events,” explains registered dietitian at Nutrition Rewired, Erin Kenney.2Rewired, N. (n.d.). Home. Nutrition Rewired. Retrieved January 9, 2024, from https://nutritionrewired.com/
How Does Carb Loading Help Performance?
By carbo loading, you can avoid hitting the wall or bonking during endurance exercise.
Hitting the wall in a marathon occurs when your body runs out of fuel, a.k.a. carbs. Therefore, your pace slows, and your muscles may start cramping and feeling fatigued.
Through carb loading, endurance athletes store excess carbohydrates in the liver, making it easier for their bodies to release them during races and long-distance runs.
“When carbohydrates are all used up and blood glucose is low, the runner will rely more on fat for energy, and the pace will slow down because energy (ATP) is produced more slowly from fat than from carbohydrate,” explains Dr. Jason Karp, exercise physiologist, run coach, and author of Running a Marathon for Dummies.
“So, not carb loading before a marathon simply means the carb fuel tank may not be as full as possible, and the runner will fatigue earlier in the race and slow down earlier.”
Carbs help with hydration, too. For every gram of stored glycogen, four grams of water are stored.
“Carbohydrates help hold water. This hydration is a critical part of race day as well,” says Gina Capone, a runner, dietetic intern, and co-host of the We Run This podcast.3We Run This. (n.d.). Spotify. Retrieved January 9, 2024, from https://open.spotify.com/show/53KeF3aO2jnJC39iCgdQ3U
Buckingham notes that while carb loading is key for races longer than two hours, it has been shown to help athletes in shorter, high-intensity races lasting less than two hours, as well.
“The reason for this is that the body will start to slow your pace down if it senses your carbohydrate levels getting too low,” explains Buckingham.
How Should I Adjust My Diet Before A Race?
Carb loading involves increasing the amount of carbohydrates at every meal and snack in the days leading up to your race.
Instead of one piece of toast, have two. Instead of half of a baked potato, eat the whole thing. Have carbs replace fat and fiber in your meals.
Capone suggests high-carb meals in the days before the race.
Three to Four Days Out From Race Day
Your plate leading up to the race should consist of:
- 50% carbohydrates (rice, legumes, whole grains, starchy vegetables like sweet potatoes, etc.)
- 25% protein (lean meat, fish, poultry, cheese, etc.)
- 25% vegetables (leafy greens, cruciferous vegetables, etc.)
The Morning of the Race
- 3-4 hours before the race: 1.5-2.5 grams of carbs for every 1 kg of body weight
- 1 hour before the race: A smaller carbohydrate snack (banana, bar, piece of bread)
- 5-7 mL of water/electrolytes fluid per 1kg of body weight
Sports dietitian Dana Eshelman notes that research4Wee, S.-L., Williams, C., Tsintzas, K., & Boobis, L. (2005). Ingestion of a high-glycemic index meal increases muscle glycogen storage at rest but augments its utilization during subsequent exercise. Journal of Applied Physiology, 99(2), 707–714. https://doi.org/10.1152/japplphysiol.01261.2004 shows a 15 percent increase in glycogen storage with a carb-heavy breakfast in the 3 hours before an event. But, don’t do this without practice.
“Carb-heavy meals, without practice and nutrition training on the gut, can cause extreme stomach upset,” she warns.
When Should You Start Carb Loading?
Carbohydrate loading generally begins about 3-4 days before race day (although some can start with a high-carbohydrate diet as many as 7 days before).
At this time, you gradually increase your carb intake per meal while eating less fat and fiber.
Which Are The Best Carbohydrates For Runners?
It’s important to keep in mind that our body stores carbohydrates best from starchy carbohydrates, says Kenney.
Good simple carbohydrate fuel sources for enhancing exercise performance include:
- Potatoes
- Pasta, Couscous (here’s a delicious aglio olio recipe),
- Rice
- Oats
- Pancakes
- Bagels, English Muffins, White Bread
Related: 11 Carbo Loading Sources For Runners
The idea is to eat more carbs than you normally would but still keep a balanced plate. Some meals to eat in the days leading up to the race include:
- Pasta with vegetables and shrimp
- Farro or rice with chopped apples, arugula, shaved parmesan and goat cheese, pecans, salmon or chicken
- Potato boats stuffed with spinach, mushrooms, tomatoes, and mozzarella
The day before the race, stick to only simple carbohydrates because they are easy and quick to break down and use as energy. Complex carbohydrates are slower to break down in the body.
8 Mistakes That Could Sabotage Your Race
#1: Eating All of Your Carbs At Once
The most common mistake runners make ahead of their marathon or half-marathon is that they plan to carb load the night before at the infamous pasta dinner.
This is a big mistake because it does not give your body ample time to replenish its stores. It can also leave you lethargic the next morning.
Runners should aim to build up carbs 3 to 4 days before the race rather than all at once.
#2: Depleting Carbs Before Loading Carbs
It was once believed that runners needed a “carb depletion phase” before loading up on carbs to fully stock their fuel stores. This phase involved doing high-intensity exercise just seven days before the race and then not eating carbs for three days.
Carb depletion involves a risk of injury and decreased confidence because it can make runners feel, well, terrible—cranky, sore, and fatigued.
The risks aren’t worth the potential dip in physical performance, and high carbohydrate intake should be the best plan of action in the days leading up to the race.
#3: Overeating
Still, carb loading does not mean you “stuff yourself” to get fuller muscle glycogen levels.
You are simply adjusting each meal to have a larger carbohydrate component. Buckingham notes that overeating (which is common due to nervousness) is not what you want.
#4: Freaking Out About Weight Gain
On the other hand, gaining weight while carbo-loading is natural. That’s because carbs help you retain water.
Remember that for every gram of stored glycogen, you’re storing 4 grams of water. If you gain some weight, that’s actually a good thing. It means your body has the fuel and hydration ready to race.
#5: Eating Too Much Fiber
As you increase your carbs, runners should reduce their fiber intake in the last three days before a race. Fiber can be taxing on the GI system.
Therefore, instead of carbo-loading with whole wheat toast, which has a high fiber content, choose white bread.
Buckingham says this gives the GI system a break and reduces the chance of GI distress during the race.
#6: Not Practicing Carb Loading Before Race Day
You never want to “try” something new on race day.
Personally, I always practice my carb-loading strategy before a couple of my long runs before race day. It helps me see how my body responds to the higher-carb intake and gives me a chance to tweak things if needed—so there are no surprises when it really counts.
Practicing will help you dial in your carbohydrate loading plan, just like you dial in your race nutrition plan. Once you know what works best for you, pre-plan your meals for the last three days so you don’t stress about what to eat.
Related: Marathon Training Meal Plans (free download!)
#7: Not Eating Enough Carbs
Runners typically eat healthy.
But eating lots of vegetables and smoothies will not give your body the carb fuel it needs for your race.
In order to properly carb load, runners should aim for 8-12 grams of carbohydrate per kilogram of body weight, explains Buckingham. For a 160-pound individual, that’s 580-870g or 2,300-3,400 calories from carbohydrates alone.
“This is also why runners need to limit the number of other foods they’re eating, like fat and protein,” says the sports physiologist.
“Eating 2,000-3,000 calories from carbohydrates without any fat or protein is already close to the daily calorie recommendation. If runners do not also limit their fat and protein consumption, they could see excess weight gain leading up to the race.”
#8: Not Drinking When Carb Loading
Not all carbs are created the same, notes Capone.
There are different types of sugars: fructose, sucrose, and glucose. Different carbohydrates have different transporters into the bloodstream. Therefore, runners need to be mindful of what they’re drinking with what carbs they’re eating.
“Sports drinks, such as Gatorade, contain fructose, glucose, and sucrose, making it one of the best liquid sources of carbohydrates for athletes. Sodium helps with the transportation of glucose, meaning sodium is an important part of carbohydrate utilization,” she explains.
So, while consuming carbohydrates is important, it’s also important to properly hydrate with sugars and salts during activity, not just before the race.
Carb loading properly before race day can be the difference between a PR and a DNF for runners.
If you want to comprise the perfect sports nutrition plan for your goals, consider meeting with a nutritionist who can assess your dietary needs and guide you to the perfect training diet.
Here are a few day-to-day popular diets for runners to browse through:
I didn’t know the issue about the importance of reducing fibre. Interesting. Am doing your ultra plan for improvers. Not so much a plan, but a way of life! It is REALLY GOOD. Everyone in my club is amazed at the distances I’m covering on LSRs. Nice one, Thomas.
Tim!
Glad you’re enjoying the training, and the Carb loading tips from Whitney!
Let us know how you get on in the ultra!
Thanks,
Thomas
I personally think carb loading doesn’t need to be so difficult or scientific. Eating a good pasta dinner the night before a marathon seems to work just fine. In 180 marathons, I haven’t ever bonked or wish I had more glycogen stores in me.
Glad to hear. Whenever I try to carb load the way I ‘should’, I get really depressed and nauseous. I guess disturbing the balance/way you eat so drastically isn’t healthy or beneficial for everyone.