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How Do I Fuel For IRONMAN?

A primer for fueling your efforts to race-day success

by Jordan Blanco

How many times have you heard the phrase “nutrition is the fourth discipline of triathlon”? Strictly speaking, it should be nutrition and hydration, but the point is that when you’re competing in endurance events that last up to 17 hours, you need an eating and drinking strategy that will fuel you all the way to the finish line.

Ask fellow triathletes about their race nutrition strategies and you will often hear stories of bonking, stomach cramps and GI distress. Admittedly, there are no one-size-fits-all approaches to fueling and hydrating during IRONMAN events, but with some deliberate testing and practice you can develop a personalized plan that works for you on race day.

What and how much should you eat?

Carbohydrates are the most important fuel for endurance athletes, and it’s good practice to know how many carbohydrates are in a given portion of your preferred nutrition. Your taste buds will help determine what you choose to eat, but there is a bounty of products—bars, gels and chews—that have been designed with athletic performance in mind. Best practice is to select products, which contain multiple sources of carbohydrates (glucose and fructose) as this mix of carbohydrates promotes enhanced absorption.

Pro tip: Check what nutrition will be provided on your chosen IRONMAN racecourse as you evaluate your fueling options.

How much you should eat is a matter of striking a balance between giving your body sufficient fuel and tolerating the intake. If you consume too few calories, you risk bonking or underperforming; too many calories and you could experience GI issues as your gut is unable to process the nutrition, especially at race effort.

As a general rule of thumb, endurance athletes should aim to eat 60-90 grams of carbohydrate per hour during IRONMAN events, with athletes typically able to consume more calories and fluids during the bike leg and fewer calories during the run portion of the event.

What and how much should you drink?

When you are exercising, fluids are lost through sweat, respiration, oxidation of what you’re eating as well as the output of bodily waste. Even a small percentage loss of bodily fluid can be harmful to both performance and your overall health. When competing in IRONMAN events, you should start the event well hydrated and aim to replace most of the water and some of the electrolytes (sodium, potassium, magnesium) as you go.

The rate at which you sweat varies not only by the individual and the level of exertion, but it is also subject to environmental conditions, as even small changes in temperature and humidity can increase the amount of sweat produced. Your goal in racing is to drink when thirsty while also being mindful of your sweat rate and aiming to replace most of what you sweat out. Caution: it is not advised that you drink in excess of your sweat rate. Thankfully, it’s relatively easy to test your sweat rate at home, using a scale to weigh yourself before and after workouts.

Pro Tip: Calculate your sweat rate by following the steps in this article. Be sure to test on the bike and the run to compare notes. Also, aim to test in similar environmental conditions to those expected on race day.

Remember, you’re not just losing water when you sweat—you’re also losing electrolytes. Sodium is an especially critical electrolyte, particularly for endurance athletes with a high sweat rate, because compared to the other electrolytes, it has the highest concentration in sweat. It’s not as easy to test your sodium losses during workouts at home, although laboratory testing is available, but you can experiment with different levels of electrolyte intake in training and lower priority races to evaluate what works for you. In hot and humid races, athletes may benefit from a sodium intake of 500-1,000 milligrams per hour. Many performance nutrition and hydration products include sodium, so be sure to check the product labels to know how much you're putting in your body.

Test everything in training

Race simulation sessions during training and lower priority races are the perfect time to test out your nutrition and hydration plans to ensure your body responds appropriately at race intensity. A good approach is to start by fueling on the lower end of carbohydrate intake ranges and if you are successful and do not experience any gut issues, increase the intake during the subsequent session until you reach an optimal balance.

Often times athletes focus their nutrition testing on bike-run "brick" workouts but neglect to test out nutrition plans during swim-bike workouts. After the completion of the swim leg in an IRONMAN, athletes must make refueling a priority, but it is also a time when the stomach is sensitive, especially if you just finished a saltwater swim and ingested any seawater. Be aware of how your stomach feels and how you respond to nutrition after a swim.

Race nutrition and hydration is highly personal, but it doesn’t need to be a mystery. Being diligent in training about planning and testing your fueling strategy over multiple sessions will pay dividends come race day.

Jordan Blanco is a multiple-time IRONMAN Hawaii finisher, IRONMAN certified coach and founder of Avid Endurance. She lives in San Francisco, California.