The Top 5 Nutrition FAQs From First Time Ironman Athletes

Training for an Ironman can be a pretty overwhelming activity.

Not only are you looking to master swimming, biking and running(!), you need to learn about nutrition, fueling, equipment, and about one million other things.

The good news is, if you’re feeling overwhelmed when signing up for and/or training for your first Ironman, you’re not alone!

Here, we’ve compiled the top nutrition questions asked by athletes following our Half Ironman training plan and Full Ironman training plan.

For other nutrition related details, check out our Ironman nutrition guide as well.

How many calories do you burn during Ironman?

Another way to ask this same question is to ask “How many calories do you need to eat during an Ironman?”.

The short answer, a lot.

The longer answer, depends on your body weight, metabolism, and a few other factors.

For example, a 130lb woman will expend roughly 7,290 calories, and a 200lb man will expend roughly 10,890 calories, all within the race itself. Here’s how that breaks down:

  • 130lb Woman:
    • Swim: 10cal/min x 90min swim = 900 calories
    • Bike: 11cal/min x 6 hour bike = 3,960
    • Run: 9cal/min x 4.5 hour run = 2,430
    • Total: 7,290 calories
  • 200lb Male:
    • Swim: 15cal/min x 90min swim = 1,350 calories
    • Bike: 16cal/min x 6 hour bike = 5,760
    • Run: 14cal/min x 4.5 hour run = 3,780
    • Total: 10,890 calories

There are some great calorie intake calculators out there to help you really nail down the expected calories needed for your body.

Considering the average adult expends between 1,500-2,000 calories per day, it’s easy to see how a concerted nutritional effort is needed to make it through an Ironman race without the dreaded “bonk” (aka hyperglycemia).

What should I eat while training for an Ironman?

When you’re burning 2-3 times the amount of calories per day as the average person, it’s really tempting to eat just about anything. Twinkies, ice cream, bags and bags of junkfood. It’s easy to justify… sure, but it’s not the answer to the question.

When you’re training for an Ironman, you need to properly fuel your body with 3 main types of food: healthy fats, lean protein, and carbohydrates.

The quick rule on rationing a meal is to fill your plate with 1/2 carbs (usually in the form of veggies where possible), 1/4 protein (such as chicken, fish, pork, etc.), and 1/4 healthy fat (like an avocado).

It’s also super important to jumpstart your day with a breakfast pretty shortly after waking up (or after your morning workout, if you’ve got a training session at the crack of dawn). Something like overnight oats, or even a banana and almond butter, can do wonders to jump start your metabolism, and help your body consume some ‘catch-up’ calories from all those hours you just spend sleeping instead of eating!

Also consider what’s important to drink while training for an Ironman. Water is good, Gatorade is ok (lots of added sugar), but it’s best to supplement your normal liquid intake with some type of electrolyte. Whether that comes in the form of Nuun or GU tablets, or something else, find something with limited to no added sugar or caffeine, and consume 1-2 tabs on training days.

What should I drink during an Ironman?

Ironman races themselves typically have Gatorade endurance formula as the stocked drink of choice at aid stations.

Whether that works for you or not is relatively up to you, but the one thing to hold true is this: Never try something new on race day!!

Use your training to figure out what your body will tolerate during the bike/run, and experiment with different hydration methods to find what works for you.

Either way, you need to be fueling your body with much more than water. There are plenty of options out there, but some of the most common are Nuun & GU tablets, before getting into more standard sports drinks like Gatorade.

Find something with little-no added sugar or caffeine (since caffeine can actually dehydrate you), and light enough that your stomach can handle it. You’ll be drinking pretty constantly once you exit the water.

There are calculators to help you figure out exactly how much you should drink, but a general rule of thumb is this: on the bike, take 1-2 sips of hydration fluid every 5 minutes, and on the run, drink at every aid station (roughly every mile) at an absolute minimum.

What should I eat during an Ironman?

The choices of what do eat during an Ironman are endless: goo’s, gels, bars, fruits, olive oil and rosemary covered fingerling potatoes (I saw this once…), and more.

If we think of our example above with the 130lb female and 200lb male, knowing that you can’t eat/drink during the swim, our athletes will burn to roughly 730 and 1100 per hour during the race. Now, since some of those calories come from our existing glycogen stores, and some come from existing body fat, we really only need to consume 25-50% of that number during the race to keep going.

Still though, that’s a lot of eating.

Luckily, items like GU packs, typically house 100-150 calories each, so eating 1-3 of those per hour can typically do most of the work. The hard part is finding something you like, and that your body agrees with. If it’s GUs, great, if you have to home cook yourself mashed potatoes with bacon, that’s fine too! Just make sure it maps to your expected calorie per hour expenditure.

It’s highly encouraged to test out some of the products Ironman will have at the aid stations on rest day so you don’t have to carry a full on backpack full of nutrition (who want’s extra weight anyway?). That way, if you run out of your own nutrition, you can have some confidence that what already exists on the course, won’t give you any unnecessary gastric distress.

What should I eat before triathlon training?

Before a training session (or even more importantly, before a race) it’s important to eat something easily digestible, and made of real food where possible.

While it’s going to vary widely from person to person, an easy rule to follow is you should consume .5g of carb per pound of body weight. Extra protein and healthy fat can be added as well.

In general, you’ll want to avoid lots of spice and fiber, as well as foods with very high amounts of processed sugar. It’s also important to avoid simply not eating at all. Even something small and simple like a banana and/or some almond/peanut butter, light toast, etc. can be enough to fuel your body through a single workout session.