How To Fuel An Ironman - Complete Nutrition Guide

Hours spent swim, bike and running, and perhaps even a gym session or too… But have you practiced your nutrition?

This article is available in video form if you’d prefer - you can watch it by clicking the video above

In today’s article we’re going to go through a complete nutrition guide for an ironman triathlon. I’m going to cover everything you need so you can feel confident you’ve got the nutrition side of things sorted for your race. Whether this is your first ironman or you’re a seasoned veteran and are just looking to finetune it , this article should have it all.

Nutrition can absolutely make or break an ironman and sometimes it can seem a bit overwhelming or scary. But it doesn't need to be! Nutrition for an ironman? You’ve got this!

Today’s article is split into before, during and after an ironman triathlon

Nutrition before an ironman

How your body uses fuel during a triathlon

When it comes to an ironman you have two major sources of fuel for energy, fats and carbohydrates

Almost regardless of what intensity you're doing your ironman at, you'll use a combination of the two for energy, but the larger proportion will be carbohydrates.

The average person has over 50,000 calories worth of energy stored as fat, so in relation to an ironman that's essentially unlimited because that's not going to run out by the end of the race.

However the average person only has about 2,500 calories worth of energy stored as carbohydrates, as something called glycogen, and you've only got about 90 minutes worth of top end effort.

So in relation to ironman pace, perhaps a couple of hours worth

Now if you run out of carbohydrates you’ll bonk, or hit the wall. What this means is your stored carbohydrates get to such a low level that you can’t maintain the same pace or power, and you’ll have to slow down and you will feel dreadful.

If you've ever ran past someone towards the end a triathlon and they're just plodding, look a bit vacant and generally not particularly well then that's probably what's happened to them.

So, in terms of what your nutrition focus should be during your ironman, hopefully it's clear that if we’re purely talking numbers and what stores you have available or what might run out, your focus should be on carbohydrates

But the other thing to say to round this section out is that for the vast majority of triathletes, carbohydrates are the optimal fuel source for performance. In order to race as well as you can you need carbohydrates, so don’t go low carb or follow a ketogenic diet unless you have a specific reason to do that and have worked with a registered professional.

Carbs, carbs and more carbs

The first big topic to cover is carb loading.

This is one of my favourite topics because it's often misunderstood and actually quite hard to do but if you get it right it's so helpful.

The aim of it is to maximise your body’s carbohydrates stores so that you have more fuel in the tank before you even start the race.

Now for a lot of people carb loading means eating a big pasta meal the night before, but you actually need to increase your carb intake much earlier than that.

The big points of carb loading are:

• Start carb loading about 36-48 hours out from your race. Research shows it's not necessary to do a low carb period first to be able to carb load effectively. It's also not very nice to suddenly go low carb, and in the days leading up to your race you want to feel good.

• Eat 10 grams of carbs per kg of bodyweight per day. Don’t worry too much about protein because you’ll inevitably get enough anyway, and in general aim for low fat foods. In order to carb load properly you have to eat a lot, and the focus should be on carbs as the name suggests. Lots of protein or fat isn’t helpful and will just make you feel super full.

• Aim for low fibre foods. Generally the lower fibre the better. Again, high fibre foods will just make you feel full and bloated and isn't helpful for our main aim. In a normal diet yeah, lots of fibre! But not for carb loading.

• Eat more in the morning and less towards the evening. This is one I found personally to be hugely helpful so I now always recommend it. If you eat more in the morning and taper to the evening you'll sleep much better. If you've ever eaten loads of pizza in the evening and then had the pizza sweats you'll know what I mean.

• No super hard training during the carb load period. Hard training damages muscle tissue which impairs its ability to store carbohydrates as glycogen. Remember all your training is done and so light training and activation work is all that's needed.

Those are the big points of carb loading. I’ve created a carb load guide which you can download. It’s got the amount of carbs, fat and protein in and gives you an idea of what sort of foods you could aim for.

You can adapt it to what works well for you and your dietary preferences

Drink to thrist, or drink to plan?

Next on the list is pre race hydration. There’s not too much here to say other than keep well hydrated before your race. Drink plenty of water and aim for your pee to be somewhat towards clear. Be careful of pre race excitement and exploration; so don’t go touring the athlete village or the local area in the sun if it’s in a nice location because it’s not uncommon for athletes to unknowingly get dehydrated or even sunburnt just before their race which is really not ideal.

As a side note, you might find yourself getting really thirsty when you carb load. I can’t find anything to support the exact reason why but I suspect it’s to do with the fact that you store water with glycogen, so when you’re carb loading and storing more glycogen you need more water to compensate for it.

Breakfast before an Ironman

So breakfast before your race.

Important? Not important? Big breakfast? Little breakfast?

So the answer is that breakfast is not super important. I would always recommend it if you can have it, but the aim of it is not to be super filling and power you through your race.

The aim of breakfast is to give your energy stores a bit of a top up and to generally make you feel good before your race.

The main bulk of the energy you need for your triathlon is actually from the food you've eaten in the days before your race and the nutrition you have during it, not from your breakfast.

A big breakfast is much more likely to cause tummy upset and won't actually help much with performance.

You can go off sports nutrition guidelines, but honestly I find that reasonably impractical for triathletes before an ironman given the time of day you usually will have to eat breakfast, amongst other things.

Eat something that you enjoy or can at least stomach early in the morning, ticks the boxes and that you've practiced.

Like with most race nutrition things, low fibre, low fat, low to medium protein, carb focused. My favourite in the past year has been some low fat rice pudding and a banana, and that’s served me well.

Ironman pre-race snack

If you have managed to have breakfast a couple of hours out from your race then it’s common to have something else before your race to help top your stores up again

The general advice here is 1 gram of carbs per kg of body weight, and this can be solely carb focused. Drinks or gels are perfect here, and a strategy that works well is to be sipping on a carb drink in the hour or so before your start time and then a gel 10 to 15 minutes before the gun.

Practices makes… for not ending up in the toilet

Now as with most nutrition things it’s so important to practice this all of what we’ve just mentioned.

Literally practice all of it. Practice carb loading, your breakfast, your pre race snack, practice it all to make sure it feels ok and that you don’t need to change anything.

You also need to practice your nutrition at your race pace. As you work harder the amount of nutrition you can absorb decreases. So don't just practice your nutrition at easy paces below your ironman pace and think it's OK, because it's possible that once you increase your pace or watts you won't actually be able to tolerate that same amount.

Practicing all of this means you know what to expect, how you'll feel, how feasible breakfast is super early in the morning. This is just as important, if not more important, as the hours you've spent doing the actual exercise. Otherwise all that hard effort and training you’ve put in can unravel, and we don’t want that!

Now just a quick note on how to tell whether what you're practicing is working: if you're following the principles of this article in terms of recommended amounts, practicing at race pace and you're not getting stomach upset like cramps, bloating or diarrhoea then that suggests you're tolerating it all well.

If you're getting problems then you can reduce the nutrition until you get to a comfortable level again. Keep practicing because you should be able to improve your tolerance over time!

If you're still getting problems despite reducing your nutrition to under what's suggested then it might be worth trialling a different brand or type of product in case it's something in the mix that you don't get on with.

Nutrition intake during an Ironman

If you’ve never done an ironman before then you may not know this, but generally you don’t take anything in during the swim. Well except water from the triathlete next to you. Ha.

It’s way too impractical and will be far more trouble than it’s worth.

So onto the bike leg and the big question is when do you start eating or drinking?

For most triathletes I would say as soon as possible. You want to start getting the carbohydrates in so that your body can use them. It takes a while for them to get into your system so you don’t want to leave it for too long.

But the other big thing to mention is that the bike is super, super important for your nutrition.

During the bike leg your heart rate is generally lower, you don’t have the aggravation of running and you’ve got the nutrition already available on your bike, and all of that combined means the bike leg is where you get most nutrition in.

This is the sort of nutrition intake that happens during an ironman. As you go through the race generally the amount of nutrition you take in will decrease for multiple reasons, but that's why nutrition during the bike is so important.

Your highest nutrition intake should be during the bike leg, and will gradually drop off over it until it drops further during the run

The aim during the bike leg is to consume between 60-90 grams of carbohydrate per hour.

You want to use products that contain a mix of glucose and fructose, but you might see maltodextrin instead of glucose, it’s essentially the same thing.

You've got things called transporters in your gut and these help you to absorb carbohydrates, and glucose and fructose use different transporters. You want to max both transporters out, and the rough numbers to do so 60 grams of glucose and 30 grams of fructose.

So if you have a product with both, you maximise the amount of carbs you absorb which will help your performance.

Now there are plenty of different products out there that fit the bill and this is a highly personal area.

I don’t use any affiliate links or sponsorship because I want my videos to be free from any bias so I’m not going to push you in any specific direction, but here are some of the most common ones available and how you would reach the 60-90 grams of carbohydrates per hour.

You’ve got to find a product you like the taste of, that you tolerate ok and that you can practice repeatedly with.

I would strongly advise that you start practicing your race nutrition months out from your ironman. Literally months out.

Start practicing it before your swim, practice swim bike, bike run, all of it to make sure it’s ok. The swim bike one is often neglected but you need to know how your tummy feels after an open water swim and then onto the bike.

Aid stations during an ironman - friend or foe?

Now you might be thinking that actually in practical terms it’s quite hard to get 60-90 grams of carbs per hour repeatedly. You might have the nutrition on you to start with for the first couple of hours, but after that what do you do?

Well you make use of the aid stations and whatever bike storage you have, and that might include taping things to your top tube.

Have a look at what on course nutrition is available, and you can factor that into your nutrition plan for the day. Try to practice anything you're going to use from the course nutrition to make sure you tolerate that too.

When it comes to aid stations it's far better to make sure that you get the aid rather than just trying to keep up your speed. This is one of those things which triathletes fret about a lot.

You know, if you slow down you're going to lose valuable seconds!

Sure you might lose a couple of seconds, but I can promise you that come the end of the race you are going to be extremely grateful that you got that nutrition and you will easily make that time back and more.

Hydration during an ironman triathlon

There are lots of different schools of thought on hydration and the most important thing to say is that everyone is different and there isn't a one size fits all rule.

It's up to you to find the strategy that fits you best and also match it to your race conditions and climate. However that's not actually that helpful for the most part, so let's go over some rule of thumb guidance.

Now you can drink to thirst, but for the ironman distance I'm not the biggest fan of it. It's easy to get distracted, to keep debating whether or not you're actually thirsty, worry whether you're drinking too much.. The end result is you not drinking when you really should have.

Or perhaps you go the other way and drink loads because it's hot and humid and you've got a dry mouth.

I think it's sensible to have a game plan going in, and 500 ml of fluid per hour on the bike is a good starting point for most triathletes. This is enough to help mitigate the effects of dehydration but shouldn't be so much that you over hydrate.

Then you can play around from a personal point of view and find what works best.

There are different options for the fluid itself and that depends on your fuelling strategy. This might be water and a sports mix containing carbs and salt, or it might be just water and salt without carbs where your focus is solely hydration.

The critical point is that you shouldn't just have water on its own.

I'll say it again just to emphasise it, you shouldn't just drink water on its own during your ironman.

When you sweat you lose some of a mineral called sodium, and this mineral is vital for a load of bodily different functions. So you need to replace it, especially over an ironman distance because you are going to sweat.

If you don't replace sodium with your fluid you dilute the amount of sodium in your blood and that can lead to a condition called hyponatraemia, where your blood sodium levels are lower than the normal range, and that can be dangerous.

The aim is for your fluid to contain at least 250mg of sodium per 500mls of fluid, or 500mg of sodium per litre. Some people need more and some people need less, and that's quite individual and also depends on things like the climate, but those numbers are a pretty good starting point.

It should tell you on the packet of sports nutrition products how much salt or sodium it contains.

By the way salt is the generic term we use for sodium chloride. Sodium chloride is made up of 60% chloride and 40% sodium. That means if your packet says 1g of salt there's 400mg of sodium so you can still work out how much sodium your product contains.

The last thing to add is that you could have water and then use something like salt tablets or sticks, and you'd just need to use the packet instructions there as they can vary.

Run like the wind, but don’t produce lots of it

As I mentioned the bike is the really important time to get your nutrition on board, but the run nutrition is still important.

Whilst we generally say 60-90g per hour for the bike that's often unrealistic for the run.

If you can, awesome, but otherwise its reasonable to actively aim to consume less but make sure it goes well.

Better to consume a bit less and not get tummy upset then to go for 90 grams per hour and have to walk because you have an awful stitch.

The 2 big things here are to check the course nutrition to see what the aid stations contain and then to practice it.

Don't try anything new on the day. I know it might be tempting, but if you haven’t practiced eating crisps or pretzels, or even bananas, I wouldn’t recommend then doing it during your race. Work out what you're going to use for the run portion and practice that exact nutrition in training.

A perfect example would be to do a long brick session where you practice your exact bike and run nutrition in combination, on multiple different days.

‘Do I have to use sports products for fuel?’

Now a pretty common question is whether you have to use products like gels or sports drinks. Can you for example eat sandwiches?

The answer is yeah, it's just not optimal. As much as I'd love to say you could have other things, generally it's just far better to go for sport specific products.

They're simple, purpose made, easy to digest and absorb. If you really want solid foods have a look at energy bars or chewie blocks as these can help to break up that taste fatigue but still give you what you need.

Solid food like bars or sandwiches are more likely to cause stomach upset, especially on the run leg, so just bear that in mind. If you want something more solid you're better off having it earlier into the bike leg.

Special needs bag

You get the option of picking special needs bags up roughly half way through your bike and your run. There’s lots of different things you can put in them, including nutrition.

So if you can pick them up, should you include nutrition in them and plan that in?

I would say it’s probably best not to. For one reason or another it’s not guaranteed you’ll get your bag or that whatever is in it is still as expected. It’s better to plan your nutrition strategy without that in mind, because if that fails you’re then you’re stuck and things could easily unravel.

Of course you can still include nutrition in it and see it as a bonus, but I think it’s better to plan without that, know the course and the aid stations and have that as a fall back.

Should you use caffeine during an ironman?

Now let's talk caffeine. Is caffeine useful during an ironman?

Heck yeah it is. Caffeine has clear benefits for triathletes. It reduces the perception of pain and fatigue and provides alertness, all of which are helpful for you.

Generally the advice is to use caffeine towards the latter parts of the race because that’s when you’re starting to fatigue and will really feel the benefits.

Any time after the second half of your bike is a good time to start taking it.

You can use whatever you want here as long as you've practiced it; flat coke, caffeinated gum, drinks or gels with caffeine in

These are all great options for giving a caffeine hit which will help give you that pick up which you need. Generally 1-3 mg of caffeine per kg of bodyweight is an effective dose, so what you can do is have that in one go or as multiple little hits over a period of time. The half life of caffeine is about 6 hours, so you can factor that in to consider whether you want more later in the race.

Make sure to practice this in training too to ensure that you tolerate it, as sometimes adding caffeine can cause gastrointestinal upset.

But caffeine can be an awesome tool for triathletes, as it's inevitable that you'll start to get tired, things will hurt and you're not always going to feel great...

But you've just got to keep on going even when it's tough, until you hear those words...

You are an ironman

Congratulations on completing your ironman! What an incredible achievement! Let’s imagine you have just finished and give you some quick tips on post race nutrition, because it doesn’t feel like this would be a complete guide without mentioning it.

Nutrition to recover after an Ironman

Of course you’re going to want to celebrate and you absolutely should, but you can help your body to recover, soak up that amazing feeling and probably feel much better afterwards too so that you can really enjoy it.

The best way to remember your post race nutrition is with 4 Rs

They are refuel, repair, rehydrate and rest

To refuel we want to start replenishing your body’s carb stores. The aim is 1g of easy to absorb carbohydrates per kg of bodyweight. Now you might have had enough of carby sports drinks by this point, but they are great for this. Otherwise you’ve got things like sweets, white bread or pasta, just easy, readily absorbable carbs.

To repair we want to give your body protein to help repair the damaged muscle tissue. At least 20 grams of protein here is a great start, and that could be from a protein powder, meat or fish, or protein found in milks like cow’s milk or soya milk. Any of these are good options.

You don't have to be too exact on the carbs or protein front, it's just to make you aware and prompt you.

To rehydrate, simply drink some fluid. The current advice is to replace 125-150% of your sweat losses over the 4-6 hours after your race, but let's be honest that's not super helpful haha. Instead, something like 300-500mls of fluid per hour is a good starting point and see how you feel. Essentially you just want to make sure you are continuing to drink and not just forgetting about it.

Like during your race you’ll want water plus sodium because you’ll be dehydrated, so you can either use electrolyte tablets or eat salty food.

To rest... Well that’s obvious. Enjoy the feeling of your incredible accomplishment and don’t return to training too early. Give your body some TLC and it will really thank you for it.

So ironman triathletes, that’s the end of this complete nutrition guide.

I really hope it was useful and that it covered everything for you. If you still have questions then let me know in the comments and I’d be happy to help out. But I’d also love to hear if you’ve got an ironman race coming up and how you get on with it!