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Carb Loading for a Marathon: Why, How and Sample Timeline

Marathon carb loading is relatively well-known, even amongst non-runners. The idea of being able to eat extra carbs in preparation for a long distance run is often a motivating factor for runners and those considering signing up for a race.

However, since carb loading for running has become so popular, incorrect methods are getting more and more attention – leading to less than stellar results. Understanding why carb loading can be beneficial and exactly how to approach it properly is key for success during a marathon or half marathon.

What is carb loading for running?

Carb loading before a marathon (or half marathon) involves gradually increasing the amount of carbs consumed in the days and weeks prior to the race, in order to store extra energy.

While most can already guess that this might be the case, understanding exactly when to start increasing carbohydrates and what type to consume will make or break your success.

The idea behind carb loading for running is that by increasing the number of carbs stored, the body will have extra energy to continue running for longer periods of time before it runs out.

Is marathon carb loading beneficial?

When completed correctly, carb loading can be incredibly beneficial for a marathon or half marathon. Storing up extra carbs ahead of time helps avoid hitting the wall, or “bonking”, during the race.

Glycogen is the body’s preferred fuel source for endurance events like running, and glycogen comes from carbohydrates. However, once carbs are used up, the body switches to using fat for energy. Fat takes significantly longer to convert to energy, resulting in slower, much more strained performance.

In most cases, muscles become depleted of their carb stores after about 90 minutes of running. Successful carb loading will result in extra energy to avoid depleting carb stores in the usual amount of time. In addition, carb loading helps with hydration – four grams of water are stored with every gram of glycogen.

Should you carb load for a half marathon?

The answer to whether or not carb loading for a half marathon is beneficial varies depending on a number of different factors. However, the biggest factor is the expected finish time.

Runners who take longer than 90 – 120 minutes to finish a half marathon may benefit from carb loading, as their glycogen stores are likely used up before they finish the race.

However, regardless of your expected finish time, carb loading for a half marathon is always much less extreme and less involved than before a marathon.

When to start carb loading before a marathon or half marathon?

Carb loading for a marathon usually starts about 5 – 6 days beforehand. The progression is very gradual, beginning by adding just a tad more carbs than usual. By the day before the marathon, carb loading is much more involved, and usually completed by consuming a primarily carb-based meal.

This sample marathon carb loading timeline breaks down how gradual the process truly is.

  • Mid-training plan: consume some trial carb-loading meals
  • 5 – 6 days before marathon: prep and plan for the week; incorporate a few small carb-based snacks
  • 3 – 4 days before marathon: increase carb quantities at dinner – plate is 50% carbs
  • 1 – 2 days before marathon: dinner carb quantities increase to 70%
  • The morning of the marathon: consume a breakfast of simple carbs 2+ hours before the race

Carb loading before a half marathon is usually shorter and less extreme, beginning only about 2 – 3 days before the half marathon.

Carb loading before a marathon or half marathon will boost your performance on race day. Here’s how, when and what to eat for success.

How to Carb Load for a Marathon

Marathon carb loading is about so much more than eating pasta and pancakes. The timing, planning and types of foods have a huge impact on your race day success. Here is how to properly carb load before a marathon.

Do a trial run during training

The first step to proper carb loading is to test out your meals and strategy well in advance of race day. Incorporating an abundance of new foods in the days leading up to the race might result in troubled digestion or unexpected reactions from your body.

About 6 to 12 weeks before your marathon, test out your main carb loading meal. Try out both your pre-race dinner and breakfast, as well as any extra snacks or supplements you plan to consume. If necessary, you’ll be able to adjust based on how your body responds to the trial.

Focus on Easily Digestible Carbs

Carb loading with the wrong types of carbohydrates could result in more harm than good come race day. Complex carbohydrates, like those found in whole grains, or those saturated with sugars or oils won’t have the same benefit as simple carbs.

Focusing on simple carbs, such as those in breads, bagels or pastas, reduces the digestive effort for your body and allows easy storage of extra glycogen.

Reduce Fiber in Pre-Race Meals

Depending on the diet you’re used to, extra fiber could wreak havoc on your digestive system. Keep up any fibrous foods that you typically eat before a long run, but try to avoid adding any extra or unusual foods that may contain more fiber.

Simultaneously Prioritize Hydration

While carb loading for a marathon is certainly important, the role of hydration is just as important. Hydrating your cells and digestive system in the days and weeks before the marathon will help avoid excess dehydration from prolonged sweating on race day. Make a point to increase your water intake as the marathon approaches.

Continue to Eat “Normal” Foods

With all the emphasis placed on carbs, it can be tempting to do a massive overhaul of your entire diet in the days before a marathon. However, doing so will likely result in some unexpected outcomes. Continue to consume foods that you regularly ate during training.

If smoothies and fruit have been part of your daily diet, continue to consume them all the way until the race. Focusing on adjusting the quantities of carbs you already eat, as opposed to adding new carbs will help maintain even digestion on race day.

3-4 Days Out: Increase to 50% Carbs

Carb loading for a marathon really kicks into gear about half a week before the race. By this time, runners should start to think about adjusting their diets so they receive about 50% of their calories from carbs. This could be as simple as including slightly more pasta in their dinner, or choosing pancakes for breakfast instead of yogurt.

1-2 Days Out: Increase to 70% Carbs

By the time the marathon is a day or two away, upwards of 70% of the diet can come from carbs. Simply adjusting quantities at dinner time to include more of the carb-rich food and less of the oily sauces, dressings or salads can make a big difference.

Selecting breakfasts that are dense with carbs, such as bagels, bananas or pancakes can help increase that daily carbohydrate intake as well.

Eat Breakfast on Race Morning

When most runners think of marathon carb loading, their first thought is usually the pre-race pasta dinner. However, breakfast on race day is just as important. It’s beneficial to top off your glycogen stores a few hours before the race to avoid bonking.

Yes, this might require a 4 am wake up call in order to have enough time to digest that bagel, but you’ll be thanking yourself at mile 20 of the marathon.

What to Eat When Carb Loading for a Marathon

Finding carbs that sound appealing and are easily digestible might be a piece of cake for some, but for others, it requires venturing outside of their typical diet. If you’re looking for carb loading ideas, here are some of the best foods to try.

  • Potatoes
  • White pasta
  • White bread
  • Oats
  • Bagels
  • Pancakes
  • Rice
  • Bananas

Most starchy foods are perfect for carb loading because they are packed with simple carbs that can be easily digested and quickly stored as glycogen.

Sample Carb Loading for a Race

Trying to incorporate these types of foods doesn’t have to require a radical shift in your diet. Simply selecting a few that you already consume and increasing the quantities is often enough to top off your glycogen stores. Here is a sample menu when carb loading for a marathon.

  • Breakfast: Pancakes or oatmeal with fruit
  • Snack: Banana or muffin
  • Lunch: Loaded potatoes with salad
  • Snack: Toast with peanut butter
  • Dinner: Spaghetti or fettucine with garlic bread

Carb loading for a marathon or half marathon doesn’t have to be stressful – in fact, most runners enjoy being able to indulge guilt-free in some extra carbohydrates.

The key to success on race day is planning and preparation. Taking the time to plan your carb loading, test the meals out ahead of time, and adjust based on your body’s response will help avoid bonking and keep you fueled the entire race.

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