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Carb Loading: What Is It + Why It Matters

Dana Eshelman, MS, RDN, METS I

As an endurance athlete we are taught to eat carbs, carbs, and more carbs before a race. But, we are not taught how much to eat, what types of carbs to eat, or when to eat them. Let’s get those questions answered so you can fuel effectively for your next big race!

Science + History

Carbohydrates (AKA carbs) are broken down into sugar to be used for energy in our bodies. When we are not using carbs for energy, between 1800 to 2000 calories can be stored in our muscles and liver as glycogen for when our blood sugars get low. The glycogen storage can fuel about 90 to 120 minutes of vigorous activity depending on the individual.

Research shows that athletes consuming carbohydrates to keep maximal glycogen stores in events lasting over 90 minutes can improve performance by 2-3 percent. That is significant in those longer duration activities. If you complete the 70.3 Ironman distance in 6 hours, this is improving your time by 7 to 11 minutes. THAT IS HUGE!

So, why does carbohydrate loading matter and why is this a long-time recommended fueling plan among the endurance community?

Carb loading started way back in 1969 with Ron Hill, in the European Athletics Championships. He was able to pick up his pace in the final 6 miles of the race rather than “hitting the wall” as we all have inevitably done at one time. That feeling is when your glycogen stores are exhausted and, as a result, your physical performance plummets. What did Hill do that was different? He used carbohydrate loading to his benefit.

Since then, the carb loading technique has evolved quite a bit and each individual is different in what works best for them.

The Traditional Carb Loading Technique

Phase 1: Three days of a very low carb diet + high intensity exercise

Phase 2: Three days of taper + high carb consumption

For my ultra endurance athletes, this is not something I recommend as carbohydrate depletion can increase the risk of injury and increase gastrointestinal (GI) complication during race day/ competition.

Recommended Carb Loading

This will vary greatly on current carb intake, GI tolerance, what you practiced with during training, what distance you are racing, and how your taper is. Current best practice shows it is recommended to increase carbohydrate intake to 8- 12 grams of carb per kilogram of body weight (1 lb = 2.2 kg) in the 36 to 72 hours before your race. So, if you are a 170 pound athlete, you can consume anywhere between 618 grams to 924 grams of carbohydrate in one day.

Now, you may think, “that is such a wide recommended range.” This is why individual circumstances as listed above are considered when working with a sports dietitian, so you are able to race at your maximal potential!

Sample meal plan for this 170 pound athlete at 9 to 10 grams carb per kilogram body weight:



​Carbohydrate (grams)


​Banana, medium 1 c oatmeal 2 T peanut butter 2 T honey 8 ounces orange juice

​27 28 7 35 33


​8 ounces fat free milk 1.5 c raisin bran

​12 71


​3 ounces chicken breast 1 c rice 2 T teriyaki sauce 1 c zucchini, baby carrots, mushrooms 1 gala apple 1 scoop skratch + 12 ounces water

​0 45 5 5 25 20


​1 c low fat fruit yogurt ¾ c low fat granola 1 c strawberries 12 ounces grape juice

​50 40 11 55


​12 ounces chocolate milk. 3 oz ground turkey 1 large dinner roll 1 c mixed veggies: bell pepper, sweet potato, kale

​46 0 30 10


​½ c dried pineapple ½ mango 1.5 c sherbert ½ c granola

​23 30 78 30


As you can see here, carbohydrates are spread throughout the day versus loading up just at the dinner meal before the main event. Ideally, your lunch or afternoon meal will be your largest, most carb heavy meal so you are able to digest and settle in for a good night's rest. This will also help avoid gastrointestinal complications the morning of your race.

It is important to note that you do not need to increase calories in the days leading into a race. Rather, you will slightly reduce your protein and fat intake to account for the reduced energy demand in the taper phase. Be aware that adequate protein intake helps with glycogen synthesis and can be used as a secondary fuel source in endurance events.

Be aware you will likely gain weight during this phase. It is common to see weight gain anywhere of 2 to 4 pounds. For every ounce of glycogen stored there is an additional 3 ounces of water stored with it. This glycogen and water will be readily used in the race.

As with any nutrition plan, you should not try new foods the day before or day of race day. You will want to trial these methods before long training days so you are able to see which amount of carbohydrate intake is most appropriate for you. A sports dietitian can also help you determine what method is best for you.

Cheers to successful carb loading and a phenomenal race day!

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