Planning ironman race nutrition

Your performance in any Ironman triathlon, or other long endurance race is determined to a great part by the food and drink you consume during the race. To get your nutrition right during the race, you need to think long and hard about the following things:

  1. Why do I need to eat and drink during a long distance event?
  2. What do I need to consume during the race?
  3. How do I plan my race nutrition schedule?
  4. When and where should I consume food and drink?

Why do I need to eat and drink during the race?

When you exercise, you need energy in order to keep your muscles contracting to help you swim, cycle and run. This energy comes from 3 main sources.

  • Glycogen stores in the muscles and liver.
  • Fat reserves around your organs and under your skin.
  • Proteins taken from muscle.

The longer you exercise, the more you deplete your stores. Glycogen stores tend to deplete after 90-120 minutes of intensive exercise. If you don't replace them, you won't perform as well. This is because glycogen provides the glucose that enables your muscles to work at full capacity. When relying on protein or fats you will not be able to make the muscles work as hard. This is because fats have to be broken down and then transported from fatty tissues to get to the muscle, while proteins also need to be broken down first. Also the enzymes in your muscles are faster at converting glycogen into energy yielding chemicals than are the enzymes that deal with fats and proteins.

Remember - A source of carbohydrate is required to provide glucose that muscles require to perform at their best.

Also, when you exercise, you generate waste energy in the form of heat. The hotter the conditions, the more you will need to cool yourself to prevent overheating. If you get too hot your performance will nosedive. Your body is not stupid and will try to prevent overheating by sweating. Water next to your skin will conduct heat away, either into clothes, or best of all, directly into the atmosphere from your skin. In this sweat you will also lose a certain amount of salt.

RememberA source of water and salt is required during warm conditions to replace any lost through sweat.

What should I consume during the race?

Whatever else you do, you should consume fluids, salts and carbohydrates. The obvious next question is, how much do I need?


Well, a benchmark for fluid consumption is one 750ml bottle per hour. If you are sweating a lot then this may increase. If you are not sweating very much, then this could be a lot less. The more you sweat the more fluid you are likely to need. Sweat rates vary between individuals, but the following factors are likely to mean you sweat more:

  1. Being male. Males produce a greater sweat output per sweat gland as they exercise harder1. This is probably in part due to the influence of testosterone on their sweat glands.
  2. Being of a larger build. The larger you are the more water you contain. Everything scales up and it is no surprise more sweat is lost.
  3. Being overweight or obese. Although you may not be well conditioned, fat is an insulating material and will lead to higher core temperatures. This will encourage greater sweat rates.
  4. Being fit. The fitter you are the more you sweat. As you get more accustomed to endurance exercise, your efficiency at cooling yourself by sweating increases.
  5. Acclimatisation to hot conditions. As with point 4, your sweat rate increases as you get used to hot conditions. If you train in the heat, then you sweat more at an equal intensity.
  6. Hotter temperatures or higher gravity. As it gets hotter your core temperature rises stimulating greater sweat rates. Interestingly you sweat less in outer space!
  7. Higher humidity. Humidity slows evaporation from the skin. As evaporation has the greatest cooling effect, humidity causes you to heat up and sweat more.
  8. Racial group. There is not much evidence that there is a difference between racial groups in sweat rate if they are equally conditioned.

The more you train in conditions  approximating those of race day the more you will be able to judge what your likely fluid needs will be. You are aiming to lose no more than 1-2% of your bodyweight during a typical bike leg in an Ironman. During the run you may be able to lose another 2-3%, but it is important to start the last 3 hours of your event in a well hydrated state.


Salts are lost in the sweat and consist primarily of sodium chloride (common table salt). How much salt you need varies.

All you need during an Ironman or any other race completed in one day is common salt. If you are racing over a number of days then other minerals like potassium, magnesium and zinc will be neededHow much salt you need depends on your sweat rate, and the saltiness of your sweat. As you become fitter, your sweat becomes less salty, as you adapt to conserve it in your body. There are some people who naturally have more salty sweat including those with conditions such as Cystic Fibrosis.

The amount of salt you need is typically 1g per litre of fluid lost in sweat. Bear in mind the difference between salt and sodium. Salt is sodium chloride and 1g of salt contains 0.4g of sodium. That is why in a 1 litre of many sports drinks you will find between 300-500mg of sodium.


Carbohydrates (carbs) are stored in the body as glycogen in the liver and muscles. These stores are depleted during long duration exercise. The amount we need to replace depends on our work rate and size. The more intense our work rate, the more important it will be to consume carbs. Generally speaking we need 75-100g of carbs per hour when competing in an Ironman event.


You will be able to get round an Ironman without any fats, proteins, vitamins or minerals, but undoubtedly your need for them will be increased after the event. Some products include them and taking them will probably not have a detrimental effect. In fact taking on protein during the event will probably help with post race recovery.

How do I plan my race nutrition schedule?

The first step you should take is to research your race beforehand. A long distance race takes a lot of planning to enable you to perform at your best, and possibly the most important part of this planning is your nutrition plan. Here are two real life examples to help you see what you need to do.

Scenario 1: You're racing Ironman Switzerland.

  1. Look up the race website and you will find a section on food and drink.


  1. Check the food and drink available on the bike feed stations. Check where they are. They are at: 29k-42k-62k-84k-94k-118k-131k-151k-173k. OK, about 30k before the first station then between 10-24k thereafter.
  2. Now how fast are you expecting to cycle? Lets say 30kph. Why not target feed stations 29k, 62k, 84k, 118k, 151k and 173k. They are about 1 hour apart.
  3. Underlined ones at 42, 94 and 131k have only water so I'm missing them out. You may use them if you require more water.
  4. What to pick up at each station? They have powerbar drink, water and coke, banana, powerbars and powergels. The drinks are dispensed in 500ml bottles. You will probably need at least 2 water bottle holders on your bike to ensure you have enough for 1 hour gap between feed stations.
  5. Typically pick up 2 bottles and discard 2 at each station. Don't take your favourite water bottles unless you want to lose them!
  6. Option 1 is to drink Powerbar drink throughout, with bananas and perhaps a couple of cheese and ham sandwiches broken into bite size pieces in your top tube food bag.
  7. Option 2 is to drink water and put salt tablets in them. You then consume powerbars and powergels as your carbohydrate sources. Bananas and cheese sandwiches may also be included.
  8. Option 3 is to use your own nutrition. This will be slower as you will have to carry your supplies with you. Unless you plan to carry 8 bottles you may well be short on fluid. You will have to pick up the water and add whatever carb or electrolyrte sources you have carried with you.
  9. At the final feed station at 173k it is worth drinking a bit more than you would normally to get your water and energy reserves up for the run.


  1. Check the food and drink available on the run feed stations. Check where they are. They are roughly 1.5k apart on average.
  2. Now how fast are you expecting to run? Lets say 10kph. You should reach feed stations every 10 minutes or so.
  3. They stock fruit, dried fruit, chips, pretzels, powerbar, powergels, bananas as well as coke, red bull, powerbar drink, soup and water.
  4. Typically pick up a plastic cup and drink 200ml every 2nd feed station (3k).
  5. Normally you are sick of the drink you had on the bike by this stage. Food may be hard to stomach so your best option is a mixture of gels and drinks.
  6. Option 1 is to drink water and consume 1 gel at every 2nd feed station for the first half and then just coke and bananas for the last half. The caffeine and fructose will give you a boost.
  7. Option 2 is to continue with the powerbar drink all the way.
  8. Option 3 is to use your own nutrition. Use the water provided, but carry a bum bag containing sachets of cordial, your own gels or salt tablets to see you through.

Scenario 2: You're racing Ironman UK.

  1. Look up the race website and you will find a section on nutrition under the race details for the bike and run courses. IMUK is typical of many Ironman triathlons in that there are separate transitions for T1 and T2. Typically you need to plan what items you will put in each transition bag. In nutritional terms you may want to put some solid foods, salt tablets or carb drink sachets in the bag for the bike leg. For the run leg bag you may want to put in gels and/or salt tablets.


  1. Check the food and drink available on the bike feed stations. Check where they are. There are 2 feed stations on each of a 3 lap course. You will need to use every feed station.
  2. You will encounter a feed station every 25k which probably equates to somewhere under an hour. You will need to swap for two new bottles each time whether or not you've finished your current bottles.
  3. They have Gatorade, powerbars and water. I assume the drinks are dispensed in 500ml bottles, you need to check this out. You will probably need at least 2 water bottle holders on your bike.
  4. Your options are similar to Ironman Switzerland, but this time there are no bananas or gels. If you plan to use these you will need to carry them in a top tube carrier or in your cycling jersey/trisuit back pocket.
  5. Again make sure you top up slightly more than usual at the last feed statino to carry a reserve into the run leg.


  1. Check the food and drink available on the run feed stations. Check where they are. They are roughly 5k apart on average. Note that this is longer than in Switzerland.
  2. Now how fast are you expecting to run? Lets say 10kph. You should reach feed stations every 30 minutes or so.
  3. They stock Gatorade, powergels, water, bananas as well as Pepsi.
  4. Typically pick up a plastic cup, steady your pace and drink 350ml every feed station (5k).
  5. Consider using the Pepsi during the 2nd half of the run. Once you've started on it, stay on it, as you'll rely on the increased rate of carbohydrate absorption and caffeine from it by this stage.

You may notice that the UK event will require more planning on our part as not so much is provided. You need to be more self sufficient and carrying food on the run could be sensible.

When and where should I consume food and drink?

 There are some places and times during an endurance event that are not so suitable for feeding and drinking. You should account for these as you plan your event nutrition. Things to consider are:

  1. Uphill efforts on the bike or run are more demanding on the body. The digestive system tends to shut down making it harder to eat and drink. Don't bother trying.
  2. Downhill sections on the bike can be tricky if wet or windy. Again don't try eating or drinking on these sections.
  3. It is not easy to eat or drink while swimming. You'd only attempt this if you are swimming for more than 5k. Just make sure you've had enough before you start the swim.
  4. Practice eating and drinking on the bike, when riding solo and in groups. In Ironman you could easily find yourself with riders around you for extended periods of time.
  5. Practice drinking when riding medium hard. During races this will be how you are feeling. You need to get used to it.
  6. Don't forget you can take smaller sips if the conditions demand it.
  7. Try to drink and eat when you will lose least momentum, for instance a flat or downhill section with the wind behind you.
  8. On an Ironman run you could choose to walk/slow jog through feed stations to make digestion easier. Don't let it be the catalyst for slowing down though.
  9. Beware of littering. It won't slow you down, but is not pleasant for others.