Carbohydrate Loading For Endurance Athletes

Carbohydrate Loading: What’s The 411?

Carbohydrate loading involves consuming a higher quantity of dietary carbohydrates ~2 days out from an important race or competition, resulting in supercompensated glycogen stores. Our muscle cells store more carbohydrates than they otherwise would, which improves performance in events where glycogen is a limiting factor. So, if you’re participating in an important endurance event or longer sporting game (~90 minutes) and you have goals beyond only finishing or just having fun, then carbohydrate loading is something to consider.

What Is Glycogen And Why Is It Important?

The human body breaks down dietary carbohydrates, converts them to glucose (sugar), and then transports that glucose through the bloodstream to organs like the brain, kidneys, muscles, and fat tissue. Any glucose that is not immediately used as fuel for cells is stored primarily in the muscles and liver as glycogen for later use, such as energy production during exercise.

Muscle glycogen stores act as a source of energy for exercise and accumulate ~400-800g of glucose. Liver glycogen stores maintain blood glucose levels and can hold ~80-100g of glucose. Our blood contains 0.9g glucose/liter of blood at any given time. In total, this amounts to ~1400-2000 calories of stored carbohydrates in our bodies alone. Keep in mind that our bodies store 3-4g of water for every 1g of stored glycogen. This can increase total body weight, but it’s temporary and will resolve after race day.

How Is Glycogen Related To Performance?

One of the reasons athletes can train day after day and session after session is because they restore depleted muscle and liver glycogen levels by eating enough carbohydrates. When muscle glycogen stores drop too low, exercise intensity output decreases and performance can be impaired. When liver glycogen stores are depleted, blood glucose drops. This can negatively affect physical and mental function and lead to fatigue.

Who Should Carb Load?

Carbohydrate loading is for those who are racing and competing in events over 90 minutes that require sustained or intermittent exercise. Examples are half marathons, full marathons, ultramarathons, ~90 minute soccer and ice hockey games, Olympic distance triathlons, half Ironmans, full Ironmans, and Spartan beasts and ultras.

For events that are less than 90 minutes, carbohydrate loading isn’t necessary because our bodies have enough stored glycogen to get us through those events so long as we consistently consume enough dietary carbohydrates.

How Do You Carb Load?

Consume ~8-12g/kg BW of carbohydrates per day 36-48 hours before your race or competition. This amounts to ~500-750g of carbohydrates for a ~140lb individual. Adequate energy availability for women is necessary for optimal glycogen storage, so carbohydrate loading likely won’t lead to performance gains if you’re under-consuming calories.

What Should You Eat?

We should strive to consume mostly quality, complex carbohydrates that are rich in fiber and micronutrients in our day-to-day diet. That being said, it is extremely difficult to hit the recommended carbohydrate loading quantities with those types of carbs since they are more voluminous and satiating. Additionally, consuming fibrous carbs before a race or competition can cause GI issues for some athletes.

Many follow a 72 hr low-residue (low fiber) diet to significantly reduce bowel contents for race day and to offset the storage of additional glycogen and water by reducing the mass of gut contents. This can be particularly important for those who tend to experience GI issues when they exercise.

To implement a low-residue diet, consume lower volume, lower fiber, and more calorically dense carbohydrates:

Sports drinks
Pretzels
Pop tarts
Rice crispy treats
Gummies
Cereal
Pasta
Potatoes
Bananas
Applesauce and other pureed, low fiber fruit
Sweetened dairy products
Drinkable carbohydrates like Skratch labs, UCAN, Carbo Pro
Pulp-free juices
Refined carbohydrate products like white rice, white bread, and white bagels
Maple syrup
Jam
Pancakes and toaster waffles
Oats
Lower fat and higher carbohydrate baked goods
Granola bars

Avoid higher fiber grains and high fiber vegetables and fruit if you’re prone to GI issues. It may also be worthwhile to reduce your intake of high FODMAP foods in the 48-72 hours leading up to your event. FODMAPs are short chains of sugar molecules that are fermented rapidly in our large intestine by our gut bacteria and can also draw water into our intestinal tract. This causes some not so fun gastrointestinal symptoms in sensitive individuals.

What About Other Macronutrients, Like Proteins And Fats?

It’s much easier to eat more carbohydrates in the 2 day period before your event by lowering your fat intake. And let us be clear: lower fat doesn’t mean zero fat! But, having thick and creamy sauces, cooking with large amounts of oil and butter, and having heaping tablespoons of nut butter probably aren’t going to make your stomach feel that great when you’re trying to eat a lot of carbohydrates. Additionally, eating meals higher in fat before exercise can cause GI issues for many.

You also might want to opt for leaner protein sources, like protein powder, egg whites, tuna and white fish, shrimp, tofu, pork tenderloin, and 96/4 ground meats. Now, you do want to try to get protein in when you can, but ultimately the most important thing is eating enough carbohydrates during this protocol.

Example Day of Carbohydrate Loading For ~140lb athlete (~10g/KG BW of Carbohydrates Per Day)

Low FODMAP and Low Fiber

Breakfast: Pancakes and Cereal

1.5 cups (54g) cheerios (any low fiber cereal will do), with milk of choice
1.5 servings (80g dry) of pancake mix (Kodiak Cakes, for example)
4 tbsp (60mL) maple syrup
50g banana (to put into the pancakes)

Lunch: “Fried” Rice

50g bell peppers
40g carrots
15g green peas (ONLY 15g!!! More is higher FODMAP)
25g yellow squash
25g zucchini
1 whole egg
135g egg whites
2-3tbsp coconut aminos
213g cooked rice if using microwavable rice from brands like Grain Trust. Otherwise, 2 cups cooked rice

Dinner: Pasta

2 servings (4oz DRY) brown rice pasta (Jovial). Regular pasta is higher FODMAP
2 slices of sourdough bread
1tbsp olive oil
1tbsp basil
60g grape tomatoes
2oz chicken breast

Low FODMAP pasta recipes:

Snacks:

2 Nature’s Path waffles with 2 raspberry Huma gels
1 Cascadian Farms chocolate chip granola bar
1 serving (~28g or 23 sticks) pretzel sticks

Smoothie

1 cup frozen strawberries
2 tbsp (30g or 30mL maple syrup)
1 cup (240mL or 240g) pulp-free orange juice
120 g banana
2 scoops UCAN or other plain drinkable carbohydrate

637g carbohydrates, 45g fats, 92g protein

For less carbohydrates, have one gel, one scoop of drinkable carbohydrates, 3oz dry pasta, 1.5 cups (177g) rice, 1 serving (53g dry mix) pancakes.

For more carbohydrates, increase servings of all carbohydrates in main meals and add in an additional high carbohydrate snack, such as graham crackers or a rice crispy treat.

For more fat, add more olive oil to dinner, some nut butter or chia seeds into the smoothie, or butter or diced nuts into the pancakes. For less fat, omit olive oil from dinner.

For more protein, add a scoop of protein powder to the smoothie, have 4oz of chicken breast, and four servings of egg whites (180g), or add in another egg.

Final Notes

Lastly (and this is very important!), the first time you carbohydrate load should not be right before your event! Practice carbohydrate loading ahead of time. We suggest practicing carbohydrate loading for one of your long runs or longer training days. Take note of what worked and what didn’t, and then adjust accordingly for your actual race and competition day.

Sources

Akermark, Jacobs, Rasmusson, & Karlsson, 1996
Balsom, Wood, Olsson, & Ekblom, 1999
Burke et al. 2011
Burke et al. 2019
Bussau, Fairchild, Rao, Steele, & Fournier 2002
Hawley et al., 1997
Hyman, 1970
Karlsson & Saltin, 1971
Sherman, Costill, Fink, & Miller, 1981
Tarnopolsky et al. 2001
Wohlgemuth et al. 2021