How to Fuel for an Ironman Triathlon


, by Renee McGregor

Photograph by: mh90photo

For those of you embarking on your first Ironman or long-distance triathlon, it’s unlikely that the concept of swim, bike, run is new. However, while you may appreciate the importance of the transition between disciplines, stepping up to this distance and level of endurance is always going to be a challenge.

One thing that is sometimes overlooked is that the way you fuel can make or break your race, especially during long-distance events. And while most of you will be aware of the role nutrition plays with regards to fueling and recovery, you may not be aware of how integral it is to optimal performance.

Ensuring that you make the appropriate nutrition choices around your training will not only help you to maintain a consistent effort day after day, but will also help you to maintain motivation and encourage adaptation. In addition, studies have shown that timing of nutrition has an integral role to play in hormonal balance, bone health and maintaining your immune system. I always say, “a healthy athlete is a happy athlete!”

Carbohydrates are key

Carbohydrate is the key fuel source for exercise as it is broken down into glucose - the body’s preferred currency - and utilised by the body to provide energy.

Photograph by: ChrisVanLennepPhoto

Carbohydrate is stored as glycogen within the liver and muscles. It is this source within the muscle that provides the most readily available fuel, releasing energy quicker than other sources. However, this storage facility is limited. If the muscles are inadequately fueled, it can lead to fatigue, poor performance and a potential increased risk of injury.

To give you some context, it takes around 500g of carbohydrate to have completely full muscle glycogen stores, with an additional 80g in liver glycogen, mainly used to maintain energy to the brain. When muscle glycogen is at full capacity, this will last you approximately 60-120 minutes when running at around 65-75% of your maximal heart rate. The quicker you go, the faster your stores will deplete. Thus, for those of you training most days, your glycogen stores are always slightly depleted. Additionally, this highlights how important fueling during your ironman is also going to be.

For events over 3 hours, it is recommended to consume 60-90g of carbohydrate an hour. This should ideally be in the form of glucose and fructose. Common foods that provide a source of both glucose and fructose are some fruits, vegetables and honey.

It is worth noting that the body can absorb around 60g of glucose per hour and 30g of fructose. There are some new studies emerging that suggest that this upper limit of 90g could be increased, but nutrition is very personal so it’s good to start with the recommended amount and then build your own strategy.

Choosing synthetic products to fuel your race

During an Ironman, one of the key aspects is deciding what type of nutrition you are going to use and when. Will you use just sports nutrition or mix it up with some real food?

For events over 3 hours, it is recommended to consume 60-90g of carbohydrate an hour. This should ideally be in the form of glucose and fructose.

In general, most sports fueling products available on the market will be created on the understanding that the body requires carbohydrate for intra-endurance fueling.

Similarly, with the rise in individuals taking up ultra-distance events in particular, many companies have also picked up on the importance of the need for higher concentration on sodium. In general, it is recommended to take on 700-900 mg of sodium per litre of fluid you consume.

There is also a move towards more natural products which are based on fruit and fruit juice rather than sugar mixes. While these have a place and are often more palatable, it's worth checking that they do actually deliver your energy requirements and don’t overload the system with fructose, which can be much more difficult to tolerate.

How to fuel during a race

A lot of the athletes that I work with often find that they need to split their fueling up during an event. This would mean breaking down their fueling into different 'blocks':

Transition 1: ideally as soon as you get out of the water, even before you jump on the bike, you should take some energy on. I would suggest sips from a bottle ready for use on the bike, or a half gel attached to the bottle. This might contain sports drink, but a favourite with a lot of triathletes is to decant three gels into 750ml water.

On the Bike: you should aim to fuel every 30-40 minutes. If you are going to take on solid food, this would be the time to do it as your body is most likely to tolerate it. Some ideas to practise with include:

  • Cold salted potatoes

  • Scotch pancakes

  • Peanut M and Ms

  • Pretzels

  • Wraps with filling of choice but good options marmite, peanut butter and banana, cream cheese

  • Cereal bars

  • Salted peanuts

Transition 2: as you get off the bike, pick up some gels or chews and start taking these 20 minutes into the run. To get the best out of your energy gels take them on gradually over a period of five minutes to help with absorption and tolerance.

As you approach the last 10Km, you may want to take on some caffeine in the form of another gel or gum.

Caffeine works best as a performance enhancer in those who respond to it, and the suggested dose is 1-3 mg/kg BW about an hour before training / competing. Similarly, in longer events, you may want to consider a fueling aid with caffeine 40-60 minutes from the finish as this has been shown to help with reducing perceived exertion.

Photograph by: Peter Heckmeier

Key takeaways

  • Don’t try anything new on race day – this is why you practise in training.

  • Always have a contingency: while you can have an element of control over your food choice, don’t forget that external factors can still influence it such as weather conditions, hormonal changes (particularly in female athletes) nerves, and adrenalin.

  • Remember that intra-run fueling helps to ensure that you are not only meeting your nutritional requirements, but are providing the body with the fuel it needs to respond to the stimulus of training, which is going to help you with adaptation and progression.

  • Make it individual – take on board the fundamental practices and then work out what you like. There is nothing worse than trying to consume something that you can’t stand the taste of. Find fuel that is practical and easy for you and that you can tolerate.

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