How to Fuel an Ironman

An Ironman is one of the most demanding endurance events out there. A 2.4-mile swim, 112-mile bike ride and a marathon to finish is no easy feat - it isn’t just something you roll up to with no preparation. Not only does it take months of physical training to prepare for the event, but it requires commitment to an Ironman nutrition plan.

In this guide, our specialists at OTE Sports share their best nutrition tips for an Ironman race, including a fuelling strategy that will gear you up for greatness.

Ironman Race Week Nutrition Tips

The big day is right around the corner, so what can you do in the week leading up to your Ironman to put in the best position for the race?

Remember that hydration status cannot be reversed in a few hours – in fact, it can take a few days to get fully on top of hydration. Keep checking your urine colour and aim for a light straw colour in the days leading up to the Ironman event. Sipping an OTE Hydro Tab little and often in the days and hours before the event will ensure you start the event fully hydrated.

In terms of diet, we recommend focusing on complex carbohydrates to help you build and maintain glycogen stores ahead of the race. You don’t necessarily need to ‘carb-load’, but make sure you are eating enough carbs for your body. Examples of complex carbohydrates include sweet potato, brown rice, quinoa, leafy greens, broccoli, carrots, beans, wholegrain bread and wholegrain pasta.

The Day Before

The morning before your Ironman, you should eat a breakfast with plenty of carbs. Ideally, you want breakfast to be your biggest meal of the day so you’re not digesting a heavy meal overnight. Carbohydrate breakfast food ideas include porridge, pancakes, waffles, bagels or toast.

Throughout the day, you should keep yourself hydrated and replenish your electrolytes with energy drinks. You should also snack at regular intervals, again focusing on foods rich in carbohydrates and protein (e.g. wholegrain toast, Greek yoghurt with granola, rice cakes with nut butter etc.).

You don’t need to carb-overload the night before, but enjoying carbohydrates that are easy-to-digest along with some protein is recommended. Stay clear of food which is high in fibre or fats as these can cause digestion issues.

Try to have a more restful day the day before the Ironman in order to preserve your glycogen stores.

Your Ironman Fuelling Plan for Race Day

What should I eat the morning of an Ironman?

Your Ironman nutrition plan starts before the race. The best breakfast before such a big event is one that is high in carbohydrates but also includes a portion of protein. Carbohydrates are essential for energy, and protein will help to slow down digestion so you don’t feel hungry on the start line. Consuming this around 2-3 hours before the start should allow the food enough time to settle in the stomach. Above all, your breakfast meal needs to be something that you are familiar with and trialled in training; don’t be making drastic changes on race day.

Top Breakfast Ideas

  • A large bowl of porridge made with milk, topped with a chopped banana or your favourite dried fruits and nuts. Add some extra protein by having a large spoonful of Greek yoghurt on top.
  • A bagel or a few pieces of toast with banana, peanut butter (or another type of nut butter) and a bit of honey.
  • Toast with two to three eggs for extra protein, with a banana and some of your favourite dried fruits and nuts as a snack on the side.

You should consider having a glass of fresh fruit juice alongside your water as this will help provide more calories and aid hydration. A coffee can also be beneficial because Ironman events usually start early and you might need this to wake you up! Don’t worry though, coffee does not dehydrate you like once believed, so feel free to have a cup prior to the event.

Before the Race

In the time between breakfast and race start, the most important thing is to keep hydrated.

Did you know? As little as 2% loss of body weight due to dehydration can negatively affect your sporting performance. So don’t start the race on the back foot by being dehydrated.

You may want to consume a snack an hour before the event, but if so, keep it light. Something like a Duo Bar, Anytime Bar, jam sandwich or banana would be a good idea.

Nutrition During the Ironman

This is the part of your Ironman nutrition that requires the most planning. Not only do you need to think about how much you need to be fuelling yourself throughout the race, but you need to know when to re-fuel and how to do so during the three different events and transition periods.

How many calories should I eat during an Ironman?

During an Ironman, you will likely expend between 600 and 1,100 calories per hour, depending on your height, weight, body composition, fitness levels, metabolism etc. If it takes you 10 hours to complete the Ironman, you will expend between 6000 and 11,000 calories during the race! This doesn’t mean you need to consume this many calories during the event as your body will also use your existing fat stores for fuel (typically around 1750kcal to 2000kcal). However, it is critical that you eat enough calories during the Ironman so you have enough energy and are not in a significant deficit by the end.

With this in mind, you should be looking to consume at least 3000 calories during the Ironman. Generally, the more you can consume the better, as long as you can comfortably digest it.

What is the best nutrition for an Ironman race?

Although it’s important to be aware of your calorie intake during the Ironman race, you also need to be aware of the nutritional value of the food and drink you’re consuming. We strongly recommend bringing your own fuel, such as energy bars, sports gels and hydro tabs. This way you know exactly what you’re eating and you won’t need to deviate from your training nutrition.

If you are looking to take up the nutrition options available on the course, there are few more considerations you need to take into account:

  • What is being provided along the course in feed stations?
  • How often is it available?
  • Do I get on with the nutrition provided on course?

Remember not all nutrition products are equal in nutritional content, so do your research before the race so you’re not faced with any surprises. Make sure your food sits well with your stomach, and that you are taking in enough carbohydrates and electrolytes (e.g. sodium, potassium, magnesium).

For example, the below is true when using OTE Sports products:

10 hours Ironman x 80g of carbs/hour= 800g

From consuming the above you will have taken on board just over 3000 kcal, your fat stores will also contribute around 1750kcal to this total.


During an Ironman, you want to aim to consume 60-90g of carbohydrates per hour. So, for a 10-hour Ironman, and an aim of 70g of carbohydrates per hour, you would need to consume 700g within the race.

Our body stores carbohydrates in our muscles and liver, but these stores are limited and get used up during exercise. When we run out of carbohydrates, we start to burn fat for energy. This might sound great, but when exercising at any sort of intensity, it isn’t beneficial. Without sufficient carbohydrate stores, the intensity we can perform at decreases dramatically. This is why one of the main aims during the event is to keep these stores topped up.

OTE’s Super Range has the perfect products to ensure you get in enough fuel for the entire Ironman race. The Super Carb Energy drinks contain 80g of carbs per serving and are available in two delicious flavours, Blackcurrant or Lemon & Lime. Alternatively, our popular Super Gels have 40g per serving.

How to Fuel an Ironman at Each Stage

Swim: It is very difficult to fuel during the swim! Instead, try having an energy gel 10 minutes before the start.

Transition 1: Time for another energy gel and a quick mouthful of water before getting on the bike.

Bike: During this leg aim to consume 4 x 750ml of energy drink, 2 duo bars, 2 energy gels and 2 caffeine gels. Spread the intake out evenly, never going too long before having a sip of drink. Aim to consume half a duo bar or gel every 30 minutes, saving the caffeine gels for the later part of the bike.

Transition 2: Time for another big gulp of water and another energy gel, before moving on to the run.

Run: During this there are 2 more energy gels, 3 caffeine gels and the final bottle of energy drink to consume. We would also advise having some water as well from feed stations, especially if it’s a hot day. Again, the idea is to split these up evenly during the run.

This may seem like a lot of sports nutrition, but OTE Sports design their products to be pH-neutral and so are kind on the stomach over such a long period of time.

Post Ironman Nutrition for Recovery

As soon as the event finishes, it is important to consider nutrition for recovery. You will most likely be in a calorie deficit at the end of the race and will need to consume the right food and drink for optimum recovery.

An OTE Recovery Drink, containing both protein for rebuilding muscles, carbohydrates to replenish your stores, and fluid to aid rehydration, is perfect for this. Aim to consume within 30 minutes of finishing as this is seen as the ‘window of opportunity’ to kick start the recovery process. Chances are you will probably not willingly want to consume this, but it is a case of needs must!

Nutrition Going Forward

Unfortunately, recovery shakes aren’t miracle workers, and this is only the first (albeit very important) step to recovery. After the event, look to consume small meals or snacks every 3-4 hours. Make sure these contain a portion of carbohydrates and a 20-25g serving of protein. The idea being that you are slowly providing your body with manageable amounts of food to be used in the recovery process.

Snack ideas could be:

  • A bagel with cream cheese and ham
  • A tuna pasta pot
  • Bowl of granola with Greek yoghurt
  • High protein smoothie
  • Chicken and cous cous salad

Ironman Training Nutrition

Getting your Ironman nutrition right during training is imperative. You need to have a solid understanding of what foods and drinks sit well with you and will help you perform at your best during the endurance event. The last thing you want to do is try new things on the day itself!

On top of this, you need to feel comfortable with how you’re going to carry your food and drink with you. The good thing about compact energy bars and gel pouches is they can be carried easily with you on the course. For example, gels can be neatly stored in zip pockets and water or energy drinks can be carried using a hydration belt or vest. Nevertheless, you need to practice carrying these, along with the art of consuming your food and drink mid-race, especially if you’re new to endurance events.

We hope this guide has helped you to prepare your Ironman nutrition and fuelling strategy. We can’t stress enough that you can’t underestimate the importance of nutrition on the big day! Remember to factor nutrition into your Ironman training too so you know how your body will respond to different food and drink during the event. Good Luck!

At OTE, our delicious sports nutrition products will help you to gear up for your Ironman and smash the race itself. Developed by a team of sports nutritionists, our nutrient-rich, pH-neutral products are gentle on the stomach and will help you perform at your very best. Discover our energy gels, energy bars, hydro tabs, recovery drinks and more today.