How Many Calories Are Burned During the Ironman Triathlon?

Your performance goals during an Ironman or similar long-distance triathlon can be made or broken by how prepared you are for the high level of calorie-burn during the race. If you overconsume with food or beverages, you may end up with stomach and intestinal issues and cramping, but if you underconsume, your performance will likely not live up to your expectations. Carefully planning your calorie expenditure and replacement will be key to your performance.

Calorie Expenditure

According to the book "Endurance Sports Nutrition" by Suzanne Girard Eberle, "Ironman competitors expend 8,000 to 10,000 calories or more during the race." These numbers are staggering compared to most human's daily calorie needs of 1,500 to 2,500 calories a day 2. Athletes use fewer calories in the swim portion of the race than they do during the bike or run. This is due to two factors: the lack of resistance in the water compared to on land, and the relative shortness of the swim distance in comparison to the other two legs of the race. However, this works out well for the racer, as it is also easier to eat and drink on the bike and while running than in the water.

Refueling Needs During the Ironman

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Calorie expenditures of this high level are 500 calories per hour of racing on average. Your goal is to replace 30 to 50 percent of those calories during your Ironman. This 150 to 250 calories per hour energy replacement is vital to your performance during and recovery after the race. Plan your refueling strategy for race day ahead of time based on your individual needs.

Carbohydrate Needs During Endurance Racing

Carbohydrates are the most critical nutrient to focus on during endurance races like the Ironman triathlon. According to "Nutrition for Serious Athletes," triathletes need to consume adequate carbohydrate energy at the rate of about "1 to 1 1/2 grams of carbohydrate per kilogram of body weight per hour." For a 150-pound athlete, the carbohydrate needs during Ironman racing would be 150 to 225 carbs per hour 4.

Nutrient Sources

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Carbohydrates abound on grocery store shelves and in our kitchen cabinets, but snacking during racing can be a tricky juggling act. First, you have to choose foods that you can literally eat on the go. Second, the foods you consume during racing have to be gentle enough for your body to handle under extreme Ironman conditions. Here are some popular race refueling favorites: sports drinks, energy bars, bananas, cola, sports gels, figs and crackers.

Hydration and Calorie Replacement

In "The Performance Zone," authors John Ivy and Robert Portman suggest that "a sensible ratio of liquid to solid calories is about 3:1 in long triathlons," such as an Ironman 5. When your body is overheated and overworked, hydration and refueling are critical, and you are most likely to handle diluted or full-power sports beverages better than most solid foods. As an added bonus, sports drinks help refill your calorie tank while they also rehydrate you and give you added sodium, which helps you retain the fluids you consume.