If you have already done an iron-distance triathlon, you will know the impact that getting your nutrition right or wrong can have on your race. It is thought that between 30-50% of long distance triathletes experience gastro-intestinal problems while racing. Issues can include diarrhoea, nausea, vomiting, bloating, flatulence and abdominal discomfort. That’s a lot of unpleasant race day experiences. So, if you are new to Iron-distance triathlon, it’s important to take the time to develop a nutritional plan well before race day and to use your long bike and run training to practise it.

Ironman nutrition planEvery athlete is different, so there’s no such thing as a ‘one size fits all’ nutrition plan for Ironman (or any other endurance event). But to help you develop the right plan for you, I’ve created this list of questions to ask yourself as a starting point.

  • How much carbohydrate can I consume per hour? Research suggests that 60-90g per hour is optimal, but not everyone will be able to tolerate that. You are also unlikely to be able to consume as much carbohydrate on the run as the bike. 45g per hour is a good place to start experimenting on training rides and runs, then build this up to 60g per hour or more if you can. See how your body reacts and adjust accordingly. If you are going to go higher than 60g/hr, you will need to use products that contain both glucose/maltodextrin and fructose, as these different types of sugar are absorbed into the blood stream via different routes. Research suggests that 60g per hour is the maximum for glucose, but up to 30g of fructose can be absorbed at the same time.1 Both drinks and gels are available with a 2:1 ratio between glucose/maltodextrin and fructose, eg the range from Torq.
  • How many calories do I need to consume? In long distance triathlon, you are unlikely to consume just simple carbohydrates in the form of gels and sports drinks. You will probably find yourself craving some solid foods, possibly something savoury, at some point and should plan for this. Many triathletes aim for 50% of their calories to come from liquids or gels on the bike and run and 50% from solids on the bike. The bike leg enables you to eat energy bars, pretzels, rice cakes, nuts, or mini-sandwiches, for example. But it’s important not to overdo these types or food, or you could have a nasty time with GI distress. A useful guide is 4-5 calories (kcal) per kg per hour on the bike. For example, a 75kg male taking 6 hours for the bike leg could plan to eat/drink 300-375 kcals x 6 = 1800-2250 kcals during this time. With 4kcal per gram, carbohydrate is likely to make up 80-90% of your calorie intake, including gels and sports drinks. The rest come from protein and fats. Do practise eating a range of solid foods on your long training rides to assess your individual tolerance to them.
  • Do I have a history of gastro-intestinal (GI) problems? This could be just in races, occasionally in training, or in everyday life. You might have been diagnosed with Irritable Bowel Syndrome (IBS) by your doctor. Research has shown that a history of GI issues is strongly correlated with the likelihood of experiencing them in a race. 2 If you do have such a history, read this blog post for some helpful suggestions. Taking supplements to support your digestive system such as probiotics or glutamine in the build up to your race may help, particularly if you will be competing in hot temperatures. Click here to find out more about the latest research.
  • What is my race pace? Intensity influences your ability to digest and absorb carbohydrates. The higher your pace, the more blood is diverted towards the muscles to supply them with the oxygen needed, leaving less blood than normal to support digestion. The faster your race time, the less carbohydrate you will need to consume overall. On the other hand, you may benefit from training your gut to take on as much carbohydrate as possible to help you race competitively. For more on this, I recommend reading this article by highly respected sports scientist Prof Asker Jeukendrup.
  • How fat adapted am I? Some triathletes will have been following nutrition plans that aim to improve their capacity to burn fat and spare glycogen stores with a higher fat and lower carbohydrate approach to their day to day diet. These athletes, who may have a history of GI distress in races, will require less supplementary carbohydrate and calories than others following the more traditional carbohydrate-based fuelling approach that I have outlined above. This may be a great strategy for some iron-distance athletes, although certainly won’t suit all and currently lacks robust research. It isn’t one that you can just implement on race day or a few weeks beforehand, however, as it takes time and significant changes to your everyday way of eating to become fat adapted. This is best started in the off-season or at the start of your base training. Be aware that the low carbohydrate approach is likely to affect your efficiency in using carbohydrate as fuel, which could impact adversely on race times.
  • What is my sweat rate likely to be? If you are a heavy sweater, or competing in hot conditions, you will need to give consideration to replacing electrolytes, especially sodium, above and beyond that included in your sports drinks, gels or solid foods. This may involve adding electrolyte tablets or drops to your fluid bottles. I recommend taking the free Online Sweat Test that can be found here on the Precision Hydration website to help you create a personalised plan for electrolytes.
  • How will I carry my nutrition? There are plenty of options including traditional bottle cages, a bottle mounted on aerobars, a specially designed ‘bento box’, pockets on your tri-suit, taping gels to your bike frame and using a multi-bottle fuel belt or gel flask for the run. Think about this well in advance and have a plan. Don’t forget to carry some spare gels in case you accidentally lose some of your nutrition.
  • Where are the aid stations? Study the race briefing pack to ensure that you know exactly where each of aid station is. Then develop a plan to refill your water bottles or pick up sports nutrition products eg gels. If you are going to make use of the on course nutrition, make sure that you have practised with the exact product in training and that it suits you. Find out what solid foods, eg bananas, will be available at aid stations.
  • What needs to be in my Special Needs bag? Know where this will be picked up and plan its contents carefully as part of your overall nutrition plan. Then add some spare nutrition products in case you have lost any out on the course or underestimated your calorie/carbohydrate requirements.
  • How should I split nutrition between the bike and the run? It will probably be difficult to consume solid foods on the run, as the action of running makes the process of digestion and absorption harder. For this reason, stop consuming solid foods 20-30 minutes before the end of the bike course to give them the chance to be digested. It is also good idea to reduce your calorie intake by about 1/3 for the run compared with the bike, to minimise the risk of GI distress, and to use a combination of sports drinks and gels to meet your needs together with sufficient water to stay hydrated (which helps digestion and absorption). ‘Flat Coke’ is sometimes available at aid stations on the run, and you may find this works for you.

I hope this article helps you to plan your race and that you enjoy success in your iron-distance event.

Jo Scott-Dalgleish BSc (Hons), mBANT, CNHC, is a registered nutritional therapist specialising in nutrition for endurance sport, based in London. She works with triathletes, distance runners and cyclists to help optimise both their performance and their health through the creation of an individual nutritional plan.

For more details, please visit www.endurancesportsnutritionist.co.uk.



1 Currell & Jeukendrup. Superior exercise performance with ingestion of multiple transporter carbohydrates. Med Sci Sports Exerc. 2008. 40(2): 275-81.

2 Pfeiffer B et al. Nutritional intake and gastrointestinal problems during competitive endurance events. Med Sci Sports Exerc. 2012. 44:344-51