Ironman Nutrition Strategy: How to Fuel a Long Distance Triathlon?

If you are a triathlete in the northern hemisphere, you are most probably in the build phase for your main races this season, your training is getting specific and you are fine-tuning the final aspects of your performance. As the saying goes; nutrition is the fourth discipline of triathlon, which is especially true for the long distance races. In case you take your training and racing seriously, we are sure you would have your pacing strategy thought through, tested and clearly defined before the race. Just as it would be foolish to enter an ironman race without having a clear idea about the pace you should be able to hold in each of the disciplines, we are convinced it is crucial to have your nutrition strategy defined and tested beforehand. In this blog, we look into the basics of ironman nutrition and lay out a strategy you can test and implement in your racing.

Let's start with the practical advice first

The aim of your nutrition strategy is pretty simple really - take in the highest amount of energy your body can tolerate for the duration of the race. Since carbohydrates are the most easily digested macronutrient, it is widely accepted that you should build your race nutrition on carbs exclusively. You will definitely hear stories and urban legends of athletes finishing their races on 2 gels and 1 bar only, keto warriors racing on water or an irondad carrying a tasty sandwich or baguette taped to his bike. In any case, we can assure you that neither of these strategies leads to the best possible performance.

We could destil the nutrition strategy to the following:

Consume 80 - 100g or carbs per hour in the most easily digestible form - gels or high-carb drinks composed of a combination of glucose and fructose. If you prefer some solid food during the race, you can throw in a race-day bar or chews. However, be careful to test your nutrition strategy in training and never exceed the maximum amount of carbs you are able to digest per hour. Avoid other macronutrients (fat and protein) in large amounts, although some protein on the bike might be beneficial if you can tolerate it.

Consume 80 - 100g carbs per hour using high-carb drinks, gels or chews.

What does it mean in practice? My race nutrition would look like this:

I would have the Skratch Superfuel before the race, as it releases energy slower than other drinks. This should cover me for the entire swim. The post swim gel is a good way to get some carbs in and a little caffeine kick. On the bike, I would carry my own low-carb hydration in an aero bottle and one 750ml bottle, and 2x Maurten Drink 320 in one 750ml bottle. I can digest the most carbs by using Maurten hydrogel products and I can tolerate the taste for a long time as well. It is a major advantage for me that they don't contain artificial sweeteners which always caused me trouble after 3-4 gels. I would carry Clif Blok Chews just to add a bit of variety. On the run, I would keep consuming the Maurten gels, even though by this point there is no appetite for them, that's for sure. I would throw in some iso, redbull and coke from the aid stations - once you start with redbull and coke tho, you should not stop, so stay on your own nutrition as long as you can.

My hourly carb intake on the run would be a bit lower on the run than on the bike. I believe most of us can digest better when our stomach is more or less stationary. Keep in mind that the on-course hydration usually contains carbs (I would guess around 25g per bottle) so you need to count that towards your maximum carb intake per hour! 

Rigorously test your race nutrition in training - different products work for different athletes und different conditions!

A deeper dive into the science of fueling

If you want to better understand why we have to go to the carb-digestion limit to maximize ironman performance, let’s look at what science says!

The sources of energy - fat is always on hand

There are two major sources of energy our body can tap during excercise - fat and carbohydrates. Human body has (for our purposes) an unlimited amount of energy from fat (1kg of fat represents 9.000 kcal of energy) and the game comes down to how much fat you can oxidize (burn) in an hour. The maximum fat oxidation (MFO) can lie anywhere between 0,3 - 1g per minute which depends on your training, diet as well as gender. An MFO of 0,5g/min could be considered a decent baseline, which we are going to use for the purposes of this article. We look at fat-burning and how you can enhance it in a previous blog. Higher MFO would not really influence your nutrition strategy. However, it would increase the pace you can sustain for the entire event, as it would increase the energy available to you. We will demonstrate this.

Glycogen - the carbs we store in the muscles

As mentioned above, the second source of energy is carbs. We could split the carbs into 2 categories - the carbs we carry in our glycogen stores (endogenous) and those that we consume just before or during the event (exogenous). The endogenous carbs are stored in skeletal muscles and liver. The amount of carbs in muscle glycogen stores will vary between individuals based on factors such as gender, body weight, body composition (more muscles = more glycogen), fitness level and diet (high carb diet = more glycogen), but will generally lie around 500g of carbs. Additionally, we carry around 100g of carbs stored in the liver; however, we may ignore those for our purposes, as the liver stores are reserved for our brain and cannot be utilized for physical activity.

In comes the race nutrition

The last missing piece of the puzzle then are the exogenous carbs. As stated above, we should take in as much of those as possible during a long endurance event. Why? Let's do some math - during an ironman, we will burn between 700 - 800 kcal per hour. For a 9,5-hour ironman (which is pretty impressive for an age-group athlete), this means around 7.000 kcal. Let’s say we can burn fat at 0,5g/min. That will supply 2.560 kcal during the entire event. (0,5g*60min*9kcal*9,5hours). Let’s also assume we completely deplete the muscle glycogen stores. This will provide additional 2.200 kcal (550g*4kcal). The stores we carry in our body thus provide around 4.800 kcal for the event, which means we are still some 4.200 kcal short of being able to complete the event in the given time.

There is no way around race nutrition in an ironman. Even if you are a great fat-burner and deplete all your glycogen stores, you will run out of fuel before you get to the marathon.

In comes race nutrition. In the ideal case, a trained human body is able to digest 80 - 100g of carbs per hour. By consuming 100g of carbs per hour, we are still barely able to compensate for the energy deficit of 4.200 kcal. (100g*4 kcal*9,5hours=3.800kcal), which means we will probably suffer in the last couple Ks on the run (oh well).

It is neccessary to state here, that some pro athletes are able to digest as much as 150g of carbs per hour, but those are extreme numbers not acheivable to any of us, age-groupers. 

What happens if you don’t fuel right?

Even when fueling to the max, our ironman performance is limited by the energy available to the body. If we further decrease the energy availability, the regulatory mechanism in our brain will literally force us to go slower, in order to decrease the energy consumption to match the level of energy available. In simple terms, if there is no fuel, the engine cannot run. The brain will notice you are running out of energy too fast and will switch to energy saving mode to protect you from catastrophic consequences. This is what happens when you hit the wall or feel like you are running on empty.

All being said, how do we improve our ironman performance?

I believe we have clearly demonstrated that in a long endurance event such as ironman, the energy availability is the main limiting factor of performance. So how does the actual training factor in? Well, quite heavily actually! With higher pace comes higher energy consumption, and higher share of the energy has to be delivered from carbs. The main focus of ironman training (once you have mastered the basics and build some base) is to economize your body to consume as little energy as possible at any given pace on one hand, and to be able to burn fat as fast as possible. This will allow you to increase your race pace without running out of energy. And don't forget: TEST YOUR RACE NUTRITION AS MUCH AS POSSIBLE.