The Essential Ironman Nutrition Guide

What to consume during an Ironman or Half Ironman triathlon, to ensure you stay strong right through to the finish line…

In an Ironman or half Ironman you’ll burn four times more calories per hour than normal. And yet in the latter stages of the race you’ll feel so crap that you’ll barely want to eat or drink.

The energy you need for an Ironman event comes from a ratio of 65% carbohydrate and 35% fat. Thankfully we all have enough fat in our bodies, so we don’t need to ingest additional fats during the race. However, our carbohydrate stores will run out after around 90-120 minutes.

The ingredients you need to give you energy and keep you healthy during an Ironman event are a) carbohydrate b) water c) and salt (arguably). The more palatable your nutrition choices, the more you’ll be able to consume. However, there are so many different nutrition options to choose from it can be bewildering.  Here’s what we recommend:

My Preference for Ironman Race Day:

The bike:  
– Drink water and eat Clif Shot Bloks for carbohydrate. Swallow a Saltstick capsule every hour, depending on your sweat rate.

The run:
– Consume energy gels and water throughout
– If you feel too crap to eat gels, regularly sip Coke, water and energy drink. Consume anything else you can handle, such as fruit.

Why Water and Clif Shot Bloks?

I recommend water and Clif Shot Bloks on the bike because its a cleaner combination than energy drinks and energy gels. You won’t get sticky hands and you won’t feel sick from too many energy products combined.  The other benefit is that you can measure your hydration and carbohydrate intake more accurately, as they come from separate sources (water for hydration, Shot Bloks for carbohydrate, Saltstick for salt).

By the time you get to the run, your gut will be compromised so you need to treat it kindly. Sip gels and drink water for the first hour, and then move on to Coke at every aid station. Coke is like pure sugar and it provides instant energy without your gut needing to process it first.

That’s just my preference, it may not work for you. You’ll need to do your own research on the best products for you.

How Much to Eat and Drink

In addition to knowing what you like to consume, you also need to work out how much you need to consume before and during your race. Working out your nutritional requirements is a dull and time consuming exercise, but it’s totally worthwhile – it could make or break your big race. Here are the guidelines you need:

Ironman and Half Ironman Nutrition Guidelines for Race Day

​This information tells you how many grams of carbohydrate per KG of bodyweight you’ll need to consume at various times, according to Ironman University. You’ll need to study the nutritional information on packets, and stick to products that are almost entirely carbohydrate.

4 hours before race
4g/kg of carbohydrate (both solid and liquid according to individual tolerances)
For example, if you weigh 70kg that would be 280 grams of carbohydrate.

5–7 ml/kg (1 oz. per 10 lb. bw)
For example, if you weigh 70kg that would be 350-490ml of fluid.

450–1120 mg per litre (or 32 fl. oz.) from sports drink, salt capsules or small amounts of salty food

Small amounts of low fat protein 4 hours prior (if well-tolerated in training)

2 hours before race 
2g/kg (mainly liquid and easily digested carbohydrates from foods and sports nutrition products)Fluid:
3–5 ml/kgSodium: 
450–1120 mg per litre (or 32 fl. oz.) from sports drink, salt capsules or small amounts of salty food

Up to the race
5–30 grams, 5 minutes before (gels, blocks, and liquid shots)Fluid:
Ad lib – to thirst

During the race
60-70 grams per hour (some athletes may tolerate up to 90 grams). Little and often.
Use products with a mix of glucose and fructose for maximal absorption. An energy gel typically contains 20 grams of carbohydrate.Fluid:
Maximum absorption is usually 1–1.2 liter per hour or 32 to 40 oz. Depends on individual sweat rate.Sodium:
500-700 mg per litre of fluid (or 32 fl. oz.). Salty Sweaters: up to 1,000 mg/Liter (or 32 fl. Oz)


After reading these Ironman nutrition guidelines you’ll probably realise that you’re eating less than you should before and during triathlons. It can be hard to consume so much, but it helps if you get plenty of your carbohydrate from sipping a sports drink in addition to your breakfast. During the race, the secret is to refuel little and often. I recommend setting a countdown alarm to sound every 10-minutes as a reminder to eat and drink,

Thankfully evidence suggests that the gut is trainable – in other words if you practice your nutrition in training you’ll improve your ability to handle it on race day. And so it’s 100% vital to practice your nutrition strategy regularly on long rides and runs, rather than waiting until race day itself.

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