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Ironman Nutrition Tips: An Ultimate Guide

Updated: Feb 6

Whether you're an experienced triathlete or a newcomer wondering how to fuel the training, you will need to consider nutrition. Nutrition can be the difference between crushing your session and struggling to complete it. It can also be the difference between clicking the snooze button and jumping out of bed.

standing on Ironman podium with nutrition

Through this blog I shall discuss some nutrition tips to make ironman training possible and make it easier. If you are unsure how best achieve the nutritional ideas discussed in this blog I have an Ironman Training Meal Plan to use as a starting point.


Energy Sources

Firstly lets establish what fuel you will be using when doing your training. Your body has several fuel sources, but the main two are fat and carbs. We all know where fat is stored on us and we know it is not in the muscles where energy is needed for exercise. This means it takes time to use fat as energy; it has to move from [insert fatty body part here] to our muscles.

Meanwhile, carbs are stored in our muscles as glycogen. This is very easy for our muscles to use and, therefore, is the preferred energy source, especially at high intensities when energy is needed fast.

So, you need carbs when training, this is what your body will be using. Your body will always burn a little fat, but everyone has plenty of this stored. Compare this to carbohydrates where your body stores very little, normally enough for 1 hour of exercise.

What To Eat

Now we know what energy sources we are using we know what we need to eat. You guessed it. Carbs! You want to make sure your carb stores in your muscle are full before you start your sessions. Good carb sources in our diet are starch: potatoes, bread, rice, pasta and other grains. These should make up half of each meal. If you are increasing your training increase the carbs you are eating. Use this table below to calculate how many carbs you should be eating a day.

nutrition you need when training for an ironman

If you're feeling lethargic or light headed during training it could be your carb stores are still low and you may need to be eating more carbs through the day to maintain your stores at 100% for when you want to do you exercise.

Causes of Fatigue

In this image you can see causes of fatigue. Reduced glycogen storage and low blood sugar are causes of fatigue. Glycogen is your bodies way of storing carbohydrate. Eating carbs throughout to match your energy expenditure and training load will reduce your fatigue.

nutrition causes of fatigue during ironman training

Image from: Newsholme, E. A., & Blomstrand, E. (2006). Branched-Chain Amino Acids and Central Fatigue. The Journal of Nutrition, 136(1), 274S-276S.

You can also see reduced amino acids in your blood are a cause of fatigue. Amino acids are the molecules used to make proteins. This shows the importance of eating protein after a training session. The closer to finishing training the better as blood supply is higher to the muscles immediately after training.


Make sure you get regular protein with each meal. Animal proteins are the best sources. Plants can be just as good if you combine several plant protein sources in one meal. Aim for 1.5g of protein per kilo of body weight a day. Your intestines struggle to absorb more than 30g per meal, so spread protein intake through the day.

Protein does not rot your teeth and makes a good snack to have between meals.

Just Before Training

Now you're eating carbs with each meal, when should you eat a meal to fuel a training session. 1-2 hours before your training have a high carb snack or meal. This should contain 1 - 4g of carbs per kilo of body weight. Take a look at my instagram posts for ideas. This tops up your carbohydrate stores and makes sure you have the energy to perform your session to the best of your ability.

For a diet surrounding training I have a generic Ironman training meal plan.

meal plan for ironman training


You also want to make sure you are hydrated before training. Your blood is mostly water and, like a gravy get thicker as water evaporates from it, your blood gets thicker when you are dehydrated. This makes it harder for you heart to pump blood around your body and makes exercise harder. A good gauge of hydration is your urine colour. Clear means hydrated. Other symptoms of dehydration are headaches, dizziness and poor focus.

You'll likely only need 500ml the hour before exercise for proper hydration. I have a nutrition plan for 70.3 triathlons which has more specific instructions on hydration.

Fuelling During Training

Next is eating during. See the graph below demonstrating why you should start eating from the first hour of your training. You can't replace the carbohydrate at the same rate you burn it. So begin taking it in from the first hour. There are some sugars which are better to eat than others. Eating the wrong amount, the wrong thing or the wrong time causes under fuelling and gut issues.

I have 2 nutrition plans available which discuss this in detail.

carbohydrate stores during exercise in response to eating and not eating


  1. You need to be eating carbohydrates for training and performance

  2. If you feel fatigued eat more carbohydrates

  3. Eat a high carbohydrate snack 1-2 hours before your training

  4. In training session longer than 1 hour eat carbs during. Start eating in the first hour.

  5. Eat enough calories

  6. Have regular protein through the day.

This has been my Ironman Training Nutrition Ultimate Guide. Nutrition is highly individual as people react differently to nutrition and have different preferences. For this reason it is hard to offer more specific advice than this over a blog. I have event specific nutrition plans available and offer 1-2-1 nutrition coaching to make individualised plans. See the links below.

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