Ask the Experts: What to Eat During an Ironman Race

Race day has arrived. You have put in all the hard yards, hours, and miles and now is your time to shine. While many triathlons may not have a large focus on the nutrition side of racing, Ironman racing requires you to approach nutrition as the 4th sport of the race. 

How should you fuel prior to the race start? When should you eat on the bike or run? How much should you be consuming? All of these questions can be overwhelming at first, but with proper  nutrition planning and testing in training, nailing race day nutrition can become secondhand. 

Pre-Race Fueling

While your calendar is set for race day, the fueling clock begins well before the gun goes off. Ensuring that all of your training sessions are being replenished is key to nailing the preparation phase of a race build. It is also important to note that practicing your fueling strategies is crucial. For a few big key sessions, practice using the same nutrition that you will on race day. Having ample time to iron out the details will guarantee that you will leave no stone unturned when it comes to your fueling choices. You will be able to find out what fuel works well with your gut, what does not, and what you need to consume in order to keep your energy levels topped off. 

When race day approaches, it’s important to start the day with completely full glycogen stores. Generally, this can be achieved with increasing carbohydrate intake for at least 2-3 days leading into the event. Keep in mind that for every additional gram of carbohydrate that your body stores, there will be nearly 3 additional grams of water. This means that adding a couple pounds of water weight leading into race day is completely normal, and starting off well hydrated is more important than race day weight. One mistake that many endurance athletes make in their hydration strategy is to consume too much plain water and not enough sodium. Sodium is one of the key players in allowing the fluids that you ingest to actually enter the cells. Without enough sodium, you can actually create more imbalances in electrolyte levels in your blood and muscles causing more problems. To counteract this, it’s a good idea to drink sports drinks, or electrolyte mixes with higher sodium concentration, or even just increase your sodium intake like drinking a V8 and a liter of water.

Race Day 

Race day will call for a very early wake up alarm for all athletes. You will need to be prepared to consume a few hundred calories early in the morning to ensure that you are properly fueled to begin the event. This may be hard for some athletes, so be sure to practice prior to the event! 

With the early start of an Ironman, you’re going to want to focus on eating an easy on the stomach breakfast that is low in fiber and easily digested. That means sticking with simple carbohydrates like a bagel or even rice, and possibly some fruit and just a little bit of easy to digest protein like egg or nut butter. Ideally, you should finish your breakfast at least 2 hours before your race start time. 

After breakfast (which should include your normal coffee/caffeine routine) stick with consuming another half liter or so of water until just before the start. Within 5-10 minutes before the race start, you could considering drinking 1/2 to full body of sports drink or a sports gel plus water for a final carbohydrate boost (just avoid taking in this fuel from the 30 minutes before start to 1 hour before start – you’ll be most likely to get hypoglycemic with the 30-60 minute window, before start fuel intake timing).

Bike Nutrition

Due to the length and duration of the bike leg during an Ironman, most of your race nutrition will take place here. This portion (especially the early stages in the bike leg) are at the “front half” of the race so your gut is able to absorb the nutrients much easier than when your body begins to shut down blood flow completely to the gut in the closing stages of the race. **Your body will be sending all blood flow to your working skeletal muscles, which means limited flow will be sent to the gut and results in Gastrointestinal issues! 

When it comes to the bike, there are a few things you will need to consider for your own individual needs. What type of climate are you racing in? Hot and humid? Altitude? Cool climate? What kind of power are you pushing? Why does this matter? Your individual sweat rate and the specific conditions (heat & humidity) will have an impact on fluid needs, you’ll need to have a hydration plan based on your personal needs. 

Your fluid intake plan needs to take into account the hourly amount of fluid you need (example, some athletes need about 1 liter/hour to match their sweat rate – others need half that amount and some need nearly double that – the only way to really know is to perform pre-post body weight checks when riding in similar conditions and intensity as you have on race day). 

Ensure appropriate electrolyte content – especially/most critically sodium (800 mg/liter of fluid is a good “starting” amount – though some need closer to 400-500 mg/liter of fluid, and others need 1000-1,500mg/liter). 

Finally, have a target energy (calorie, most importantly carbohydrate) intake per hour. Most folks during an Ironman will need between 40 grams (160 kcal) and 120 grams (480 kcal) of carbohydrate per hour on the bike to partially replace what is being burned on the bike. The more power that you produce and the higher relative intensity that you ride, the greater your needs will be. For example, some smaller athletes succeed by taking in about 200 kcal of carbohydrate per hour during a 6-hour bike leg and run well afterwards. Other bigger, elite male riders holding closer to 300W who take in nearly 600 kcal/carbohydrate per hour (150g/hour) from a mix of different carbohydrate types and can have successful races. Remember, every athlete is different and what works for one, may not work for another! 

Run Fuel

During the run, the total fuel intake is typically lower than on the bike. That being said, maintaining hydration and electrolyte balance is important (again – the importance of sodium), and going with more fluid energy intake is common. Consuming a caffeine liquid, such as a coke on the run is great – but generally  wouldn’t recommend starting to drink coke until you’re at least half way through the run. These types of drinks are ideally consumed more in the last 10K to 10 miles.

Common Fueling Mistakes

Three big problems that tend to occur with Ironman athletes are as follows: 

  1. Waiting too long to start a hydration plan resulting in early dehydration. The effect of this is reduced capacity to process fluids and fuel for the rest of the day. 
  2. Having too little sodium in your fluids ingested resulting in bloating at a minimum, and potentially dangerous hyponatremia (low blood sodium). Hyponatremia can result in coma and even death 
  3. Excessive fuel intake relative to the body’s needs. This is especially important if too much is taken in all at once, if the foods taken in contain too much protein or fat which take much more time and divert blood flow away from your working muscles to digest. 

The other confounding issue is early over-pacing on the bike (going too hard), and then also failing to both hydrate and fuel during that early over-pacing. This leads to dramatic reductions in performance due to the combined fatigue, dehydration, and low fuel intake relative to need.

Competing and completing an Ironman is a huge undertaking requiring your body to be firing on all cylinders come race day. While many athletes solely focus on the physical training, many can forget the importance of training their nutrition. Be sure to plan your nutrition, test your nutrition, and be confident in what you’ve done. As always, remember that what works for one athlete may not work for another, and that your best plan is what gets you to the finish line.

Mac Cassin is the Chief Cycling Physiologist at Wahoo Sports Science. He holds a degree in Integrative Physiology from the University of Colorado-Boulder and has won multiple National Championships. The experience of juggling athletic goals with collegiate and career responsibilities has taught Mac that peak performance is achievable even for those who cannot focus exclusively on training. While concentrating on exercise physiology in an academic setting, Mac competed at the World Championships, Pan American Championships and World Cups on both the road and track.

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