Ironman Nutrition Plan: The Complete 140.6 Fuelling Guide

Quick answer: what is an Ironman nutrition plan?

An Ironman nutrition plan is a written, rehearsed schedule of carbohydrate, fluid and sodium for all 140.6 miles (226km) of racing, built around what your gut can actually absorb. For most age-group triathletes that means 60g to 90g of carbohydrate per hour on the bike, 45g to 75g per hour on the run, fluid matched to your measured sweat rate, and sodium matched to how salty you are. The plan is set by the hour, not by the kilometre, and it is practised in training for at least 12 weeks before race day.

Written by Taryn Richardson, Advanced Sports Dietitian and former Sports Dietitian for Triathlon Australia.

Why does an Ironman nutrition plan need its own set of rules?

Ironman is the only triathlon distance where nutrition is almost guaranteed to decide your result. You can be slightly underfuelled through a Sprint and still run fine. You can get a 70.3 wrong and limp home 10 minutes down. Get 140.6 wrong and you are walking the last 15km of the marathon doing sums about how early you should have started drinking.

The maths is brutal. Your muscles and liver hold somewhere around 500g to 600g of glycogen (the storage form of carbohydrate your body runs on) if you have loaded properly. At Ironman intensity you can burn through that in roughly two to three hours. The race takes most age-groupers nine to 15 hours. Everything after that third hour has to come out of your pockets and your bottles.

This is the single biggest difference between a 70.3 and a full. I walked through the half in the 70.3 nutrition plan guide, and the short version is this: at the half you can get away with a decent plan. At the full, you need a rehearsed one.

How many carbs per hour does an Ironman nutrition plan need?

Start with the evidence. A single carbohydrate source, usually glucose or maltodextrin (glucose molecules joined together in a chain), can only be oxidised at around 60g per hour. Add fructose and you tap a second intestinal transporter, which lifts the ceiling to roughly 90g per hour for ultra-endurance events (Jeukendrup, 2014, Sports Medicine).

That 90g per hour figure has been poked at hard since. A 2022 review of the newer research concluded that the 90g per hour maximum should stand for now, because intakes of 120g per hour increase how much of that carbohydrate you burn without reliably making you faster, and can increase your own muscle glycogen use (Podlogar and Wallis, 2022, Sports Medicine). The same review made a more useful point for Ironman athletes: a glucose to fructose ratio closer to 1:0.8 is better tolerated and better oxidised than the old 2:1 standard.

So the race-day ceiling is not the interesting number. Your personal ceiling is. Here is how I set targets for age-group athletes racing 140.6:

Notice the run number is lower than the bike number. That is deliberate and it is where a lot of plans fall apart. Athletes hold a beautiful 85g per hour on the bike, roll into T2 feeling like a genius, keep pushing the same rate on the run and spend the next four hours regretting it.

If you are at the top of your range on the bike, then plan to drop 15g to 25g per hour for the run and make up the difference with fluid carbohydrate, which empties out of your stomach faster than a chewy bar.

I go much deeper on how to pick your own number in carbs per hour for triathlon, and it is worth reading before you set your race plan, because more is not automatically faster.

A worked example (hypothetical, so do not copy the numbers)

Say you are a 72kg athlete targeting an 11:30 Ironman: a 1:15 swim, a 6:00 bike and a 4:00 run. At 80g per hour on the bike that is 480g of carbohydrate out of your bento box and bottles. At 60g per hour on the run that is another 240g. Add the 100g you take in during the last two hours before the start and you are looking at roughly 820g of carbohydrate across race day.

That is somewhere between 27 and 33 gels' worth depending on the brand you use. Written down like that, two things become obvious: you need a system rather than a vibe, and you need to have practised carrying and swallowing that volume long before race week.

How much fluid and sodium does your Ironman nutrition plan need?

Sweat rates in Ironman athletes commonly sit somewhere between 500ml and 1.5L per hour, and sodium (the electrolyte you lose most of in sweat) varies enormously from one athlete to the next. Which is exactly why I will not give you a number here. The honest answer is that you have to measure it.

Do a sweat rate test at home in conditions that match your race, then read sodium for triathletes and work out whether you are a salty sweater or not. Those two numbers are the backbone of the hydration half of your plan.

Two rules I will give you:

• If you are drinking to a schedule rather than to thirst in an Ironman, then cap replacement at about 80% of your measured sweat rate. Chasing 100% is how athletes end up overdrinking, which is far more dangerous than being mildly dehydrated.
• If your race is hot or humid, then your sodium goes up before your fluid does. More fluid with the same sodium just dilutes you further.

For context on how small the numbers actually are: two slices of bread carry more sodium than a 600ml bottle of most sports drinks. If you are counting on your drink alone to cover a 10-hour day of salty sweating, the arithmetic does not work.

How do you carb load for an Ironman without feeling like a bloated whale?

Carbohydrate loading is well established for events over 90 minutes, and the daily targets for athletes training at a high load sit around 6g to 10g per kilogram of body mass, rising to 8g to 12g per kilogram for very heavy training or loading days (Thomas, Erdman and Burke, 2016, Medicine and Science in Sports and Exercise).

For a 72kg athlete, the top of that range is about 860g of carbohydrate a day. That is a genuinely large amount of food, and the bloating most triathletes complain about is almost always a fibre and volume issue rather than a carbohydrate issue. Swap the brown rice for white, the wholegrain bread for white, the bowl of vegetables for a smaller one, and lean on juice, white toast, honey, jam, sports drink and lollies for the last 48 hours.

The full 48-hour protocol with actual meals is in the carb loading for triathlon guide, so I will not repeat it here. What I will say is this: the scales will go up by 1kg to 2kg and that is the plan working, not you getting fat. Water is stored alongside glycogen. You are carrying your own aid station.

What should you eat on Ironman race morning?

A 3:30am alarm for a 6:40am swim start gives you a three-hour runway, and most athletes waste it.

• Three hours out: 1g to 4g of carbohydrate per kilogram of body mass, low in fibre and low in fat. White toast with honey, a bowl of white rice porridge, or whatever you have practised. For a 72kg athlete the middle of that range is around 150g, which looks like four slices of white toast with honey plus a banana and a glass of juice.
• Two hours out: sip 500ml to 750ml of sports drink slowly. Slowly is the operative word.
• Thirty minutes out: stop drinking so you are not queueing for a portaloo in your wetsuit.
• Ten minutes out: one gel with a mouthful of water, if your swim is on the longer side.

Caffeine goes in here too if you use it, and the dose should be worked out from your body weight rather than from how many coffees your mate has. I covered the dosing in caffeine for triathlon.

Never try anything new on race morning. Not a new brand, not a bigger breakfast, not the free product in the race bag (please).

How do you fuel the Ironman run when your gut has had enough?

By the time you reach T2 you have been pushing carbohydrate into a jostled stomach for six or seven hours, and blood flow has been diverted away from your digestive system toward your working muscles. Your gut is not broken. It is just busy. The body prioritises the same way it would if you were running away from a lion: heart, lungs and legs first, digestion last.

So the run plan is built differently:

• Drop to the lower end of your carbohydrate range and accept it.
• Shift from solids to fluids and gels, because liquid empties faster.
• Take small amounts more often rather than a big hit every 45 minutes.
• If you feel a brick sitting in your stomach, then walk the next aid station, sip water only, and restart fuelling 10 minutes later at a lower rate. A two-minute walk is cheaper than a 40-minute death march.
• Cola in the last 90 minutes is legitimate, not a failure. It is sugar, caffeine and something that tastes different when everything sweet has become unbearable.

Gut tolerance is trainable, and that is the good news. Repeated exposure to high carbohydrate intakes during training appears to improve how well athletes tolerate fuel, although it is still unclear whether that is better absorption or simply better comfort (Podlogar and Wallis, 2022, Sports Medicine). Either way, the practical message is the same: your gut gets better at this if you train it. The what and why of that process is in gut training for triathlon.

How far out should you start practising your Ironman nutrition plan?

Twelve weeks, minimum. Your nutrition plan is the fourth leg of triathlon, and nobody shows up to an Ironman having done three swims.

If your race is inside eight weeks and you have never measured any of this, then do not try to do all six rows at once. Pick the hourly carbohydrate rate and the sweat rate test. Those two give you the biggest return.

What goes wrong with most Ironman nutrition plans?

After two decades of working with triathletes, the failures are remarkably consistent:

1. Daily fuelling is a mess, so the race plan has nothing to stand on. You cannot put the sprinkles on the icing if you have not baked the cake. If you are underfuelled day to day, your glycogen stores are not full enough for the race plan to work no matter how good the spreadsheet is.
2. The plan is set by kilometre, not by hour. Course profile, wind and a mechanical all change your timing. Your stomach runs on a clock.
3. Copying a pro's numbers. A pro racing eight hours at 300 watts is not solving your problem. Their protocol is worth studying. Their numbers are not yours.
4. Set and forget. What worked at Busselton in November will not automatically work in Cairns in June. Heat changes everything.
5. No plan B. If you drop a bottle at 90km, what happens? If the on-course product has changed brand since last year, what happens? Write the fallback down.

If more than one of those sounds familiar, do not stress. All five are fixable with the right sequence, and almost every athlete I work with starts somewhere on that list.

Frequently asked questions about Ironman nutrition plans

Q: How many carbs do you need for an Ironman?
A: Most age-group triathletes need 60g to 90g of carbohydrate per hour on the bike and 45g to 75g per hour on the run, which adds up to roughly 600g to 900g across a full Ironman depending on your finish time. The exact number depends on what your gut has been trained to tolerate, so build it in training rather than choosing it on race week.

Q: What should I eat the night before an Ironman?
A: A low fibre, low fat, high carbohydrate dinner you have eaten before, such as white rice or pasta with a simple sauce and a lean protein. Keep the portion sensible rather than enormous, because the real loading work happens across the previous 48 hours, not at one dinner. Avoid anything spicy, creamy or unfamiliar.

Q: Can you do an Ironman on low carb or fat adapted fuelling?
A: You can finish one, but the evidence does not support it for performance at Ironman intensity. Fat oxidation cannot release energy fast enough to sustain race pace, and carbohydrate remains the limiting fuel for events of this length and intensity. If you want to go faster rather than just finish, train your gut to use carbohydrate.

Q: How much sodium do I need for an Ironman?
A: It depends on your sweat rate and your sweat sodium concentration, both of which vary hugely between athletes, so there is no single number worth quoting. Do a sweat rate test and assess how salty your sweat is, then set your hourly sodium from that. Guessing a round number off the internet is how athletes end up cramping or bloated.

Q: Is an Ironman nutrition plan different from a 70.3 plan?
A: Yes, substantially. A 70.3 is short enough that you can carry most of what you need and tolerate the top of your carbohydrate range throughout, whereas an Ironman requires you to drop your rate for the run, plan for aid station products, and solve fluid and sodium over eight to 15 hours rather than four to six.

Q: When should I take caffeine in an Ironman?
A: Most athletes do best splitting the dose, with some before the swim and the rest in the back third of the bike or early run rather than loading it all at the start. Work the dose from your body mass and trial it in training first, because caffeine on an empty, sloshing stomach late in a race can backfire.

Bottom line

An Ironman nutrition plan is not a list of products. It is an hourly schedule of carbohydrate, fluid and sodium that you have rehearsed enough times to execute while tired, hot and nine hours into the worst and best day of your season. Build the daily fuelling first, set your hourly carbohydrate rate from what your gut can handle, measure your sweat rate rather than guessing it, drop your rate for the run on purpose, and write down the fallback for when something goes sideways.

The best time to work this out was 12 months ago. The second best time is today, and 12 weeks is genuinely enough to change your race.

If you want to stop guessing and learn how to build your own plan properly, with your numbers rather than someone else's, register your interest in the next cohort of the Triathlon Nutrition Academy at dietitianapproved.com/academy.