Proper Carbo Loading for Endurance Athletes


This article is from Monique Ryan, MS, RD, LDN, CSSD, author of Sports Nutrition for Endurance Athletes.

The term “carb-loading” is probably one of the most misunderstood nutrition strategies for IRONMAN competitors. Most athletes picture plates of pasta to be consumed the night before the race, however, effective carb-loading is much different than just beefing up one meal with carbohydrates or a one-day “pig out.” Read on for the full breakdown.

What is carb-loading?
Carbohydrate loading is simply a strategy that involves specific changes to your training and nutritional intake that can maximize muscle glycogen or carbohydrate stores prior to an endurance race. For the IRONMAN triathlete, carb-loading takes place during the race taper and can be successfully executed in the three to four days before the race. While carb-loading has its challenges, it is certainly manageable if you have a thought out plan consisting of foods that you like and can tolerate in the required portions. Basically, during your race taper you have to consume enough carbohydrates to bring up muscle glycogen to the highest levels possible.

How does it work?
Your muscle glycogen levels are normally in the range of 100-120 mmol/kg wet weight (ww). These levels are constantly increasing and decreasing as you train (deplete), eat (replete), and train again (deplete). As you taper (less depletion) and eat properly (repletion), you can increase your muscle glycogen stores to 150-200 mmol/kg ww. Carbohydrate loading requires anywhere from four to five grams of carbohydrates per pound of body weight per day for three to four days. That’s about 660 to 825 grams of carbohydrates for a 165 lb. triathlete. Experts estimate that carbohydrate loading can improve race performance by one to two percent for a set distance race like IRONMAN events. For a six and a half hour finisher in an IRONMAN 70.3 event this can improve a finishing time by 4-8 minutes, and for a 13-hour finisher in an IRONMAN event (140.6 miles), this can provide a 8-16 minute boost. Can you say PR?

Will carb-loading make me fat?
Carb-loading should not increase body fat levels, but it will result in weight gain. That’s because there’s typically an increase of three to four pounds from the additional muscle glycogen and the water that is retained during this time. Remember, you’ll use this glycogen for fuel during the race, so it’s not “dead weight” that will slow down your run.

How should Athena and Clydesdale athletes carb-load?
If you are at a higher body weight, consider that your carbohydrate loading efforts may max out at 750 to 800 g of carbohydrates per day so you don’t have to go above that amount. Carb-loading for several days ensures that you have gotten the job done. Remember, you still have to fuel for the workouts on the schedule during your taper, and then eat carbohydrates beyond what is needed to store a higher than normal amount. Your well-trained muscles know how to make glycogen, you are simply providing the fuel for them to do so when at rest. If you struggle with weight management, even with the volume of IRONMAN training, keep in mind that you are only carb-loading for three to four days. While it may also seem to be a high-calorie intake, you can keep fat intake low during the taper as well. Keeping fat low also leaves room for the higher carbohydrate foods that can fuel you up. Remember, any weight gain on a proper carb-loading plan—not a pig-out plan—is glycogen and water, so there’s no need to sweat it—until race day, of course.

Do I have to eat unhealthy foods when I carb-load?
Of course, your daily training diet should consist of wholesome carbohydrates packed with nutrients including fiber. However, because of the challenges posed by carb-loading, a high volume of carbohydrate with less training (and perhaps not as big of an appetite), you need to incorporate compact sources of carbohydrate and perhaps dial back on the more filling high fiber sources. Think bagels, jam, and juice versus raw carrots and a large salad. Limiting some fibers and foods one to two days before the race will also ensure that you don’t experience gastrointestinal problems during the race. Keep in mind that you will still consume fiber containing foods when carb-loading, the only difference is not all of your carbs are packed with fiber. During the carb-loading phase, you may consume foods that aren’t on the daily menu or that you don’t consider “healthy.” Don’t stress about it—having these foods in your diet for a few days once or twice a year. This shouldn’t result in any long-term health problems.

How do I make it work for me?
Many IM triathletes may not appreciate the amount of carbohydrate foods required to carb-load. Working with a sports dietitian who can develop plans specific to your weight, food preferences, and race location can be helpful. Working with an app to add-up carbohydrates is another helpful alternative. Think ahead to your race venue, where you will be in the day before the race, and what food items are or are not available for purchase? Are you flying to a destination race or driving? Relying on restaurant foods can be challenging and time-consuming. Pack food for your race, or ship dry items ahead if needed. Scout out grocery stores on the internet and purchase simple items that can be prepared at your race accommodations. Most importantly, have a plan. Bring food with you when you go to check-in, transition, and attend the expo. Don’t leave a meal or snack to chance or delay eating—staying on schedule is key.

Can I carb-load the day before only?
It’s best to start a few days ahead so that you are not scrambling for the right foods and restaurants the day before and can focus on rest and other race preparation activities. This also ensures that you will load up your muscles with consistent effort. The day before the race, start eating early and try to get your carbs in by 6 p.m. This may be a good day to keep your fiber intake under control. Consume foods that you trust completely and go to bed early. The last thing you want to experience on race morning is to wake up feeling stuffed and not have the appetite for your pre-race meal.

What does a carb-loading menu look like?
Check out the sample menu below for ideas to fit your own tastes and lifestyle. Always remember to choose foods that you like and can tolerate. Check labels for the types of carbohydrates the foods contain, and tally the day to see if you hit your target. You can also add high carbohydrate sports nutrition supplements to your plan, your favorite energy bars, and high-carb smoothies.

2 cups low fiber cereal
12 ounces orange juice
1 large banana
2 tbsp. raisins
2 tbsp. honey
Total: 125g carbohydrates

4 ounce bagel
2 tbsp. jam
Total: 60g carbohydrates

Turkey or other sandwich filling
1 large pita bread round
6 ounces low-fat yogurt with fruit
12 ounces lemonade
Total: 110g carbohydrates

Smoothie made with 12 ounces low-fat milk, 1 cup berries, 1 banana, and 2 tbsp. honey
Energy bar
Total: 120g carbohydrates

2 cups cooked pasta or 1.5 ups ride
1 cup pasta sauce or other sauce
2 slices bread
3 ounces lean protein
1 cup cooked vegetables
8 ounces juice or flavored drink
140g carbohydrate total

2 Fig bars
Total: 50g carbohydrates

Total Carbohydrates: 605g


See what to eat and when with Sports Nutrition for Endurance Athletes. Ryan demystifies optimum daily nutrition and shows simple steps to make the best decisions about what you eat and drink.