Ironman Arizona Nutrition Report

I always get a lot of questions about nutrition for Ironman. Actually, “fueling” is probably a better term, since we’re talking about race day fuel strategy rather than day-to-day healthy eating.

Fuel is definitely the “4th discipline” in an Ironman, and in my view is as important as swim, bike and run. The longer the distance, the more critical it becomes. Many an athlete has been relegated to a slow walk half way through the marathon because of issues relating to fueling (too much, too little, or just the wrong approach).

Despite starting with a solid understanding of the theory, and with several references to build on, it still took me a lot of races to really figure out my nutrition for Ironman racing. Ironman Los Cabos was the first race where I felt that I totally nailed my nutrition plan. My subsequent races built on top of that, but still have to be tweaked depending on conditions. For example in cold weather I can absorb a lot more than in hot conditions. And in very windy conditions it can sometimes be difficult to fuel on a specific schedule, because you prioritize not crashing over taking in extra calories!

So going into Ironman Arizona, I used my Los Cabos nutrition plan as a base, but I still had a few tweaks to make:

  • in the 10 days before the race I would predominantly eat a high fat diet. Based on all the testing I’ve done, what you eat in this window has a large impact on how your body uses fat vs carb on race day. If you’ve never done this before, it will probably take longer than 10 days. I followed that protocol for Ironman South Africa which worked well for me. The change I made this time, was to reintroduce carbohydrate the day before the race, instead of 2 days before the race.
  • The biggest change I made was my race day breakfast. In the past I’ve eaten a lot of calories, mainly high carb with a bit of protein and fat. My breakfast consisted of 4 scoops of UCAN, 1 scoop of IsoPure Colombian Coffee Whey protein, and 3 small “crepes” filled with butter, peanut butter and honey. About 900 calories, a lot from protein and fat but still a decent number of carbs. Based on my testing, a breakfast higher in fat would result in a higher % of fat used as a fuel in the early parts of the race.  The reason for burning more fat is not so that I can get ripped, but so that the precious glycogen (carbohydrate) stores can be spared. Even a very lean athlete has enough fat stores to fuel several back-to-back marathons (in terms of caloric value), yet glycogen stored in the muscles and liver might be 2000 calories if you are lucky. So, the more you can spare glycogen, the better.

So, back to Arizona. Before a major race, I always do another metabolic test, at my specific power output goals on the bike, to validate both my total and my carbohydrate calorie requirements. I do this test during a long ride on the trainer, where I’m riding at Ironman race pace. Each “bucket” in the chart below is a 15 second average measurement. I just take the peak bucket any time after 3 mins into a 5 min interval and use that for fuel planning. In this case those values are 645 kCal/hour CARB and 478 kCal/hour FAT at 260 watts.IMAZ fuel test


I then make an assumption about starting glycogen (I conservatively estimated 1200 calories), before calculating the burn rate of swim/bike/run. This calculation is purely an estimate, since the actual energy requirements can vary quite a bit on race day. But it’s a reasonably good estimate, that if you are conservative in your estimations can help you plan for “worst case scenario”. It’s also a useful mental exercise to do this, just to be very aware of the different factors that affect this, so that on race day you can make some accurate adjustments based on what actually happens.

day plan


Note that the above calories are ONLY CARBOHYDRATE calories. Fat and protein have very little fueling benefit when ingested. Protein does have some benefit in that it prevents muscle breakdown, and of course fat and protein can make you “feel better”. So I tell people to eat fat and protein if they like it, or if it makes them feel good, but they need to be aware that by doing so they are using valuable “stomach space”, essentially leaving less space for carbohydrate, which is the thing that is actually going to fuel better performance. Your body can get more than enough fat to use as fuel from it’s own stores. There is no need to eat it too (other than to make you feel nice). I do take in a little protein and amino acids, but I don’t factor those in to my calorie calculations.

Ironman Arizona Race day nutrition

Ok, so finally we get to the point of this post, which is what I took in on race day

As described above, my breakfast consisted of 4 scoops of UCAN, 1 scoop of IsoPure Colombian Coffee Whey protein, and 3 small “crepes” filled with butter, peanut butter and honey. About 900 calories, a lot from protein and fat but still a decent number of carbs. Between breakfast and the start of the race, I just drank water and a light BCAA (amino acid) solution. No more calories until I got on the bike. I wish I had taken a 2nd bottle of water, because I was super thirsty by the time we started the swim. I’m guessing this was due to the dryer air in Arizona.

I use one bottle between the bars, and another bottle behind my seat. I saw a lot of people with 3 or 4 bottles on their bikes, which I think is really unnecessary. With aid stations every 10 miles you certainly don’t need 3/4 bottles. It’s just extra weight for no reason.

  • 2 bike bottles with just over 1000 calories each. I make my own simple “liquid gel” with 8oz tart cherry juice, 160g maltodextrin, 80g fructose.
  • 2 packets of power bar cola shots (200 calories each)
  • 2 gels in my pocket (200 calories)

The goal was to get through about 500 calories per hour on the bike. I managed to do this until the wind really picked up, then I was holding on to my bike more than drinking from a bottle! For 2015 I’m experimenting with the Torhans Aero 30 bottle – it has a straw so you can drink without taking your hands off the bars. Anyway, at least I was conscious of the fact that I needed to get the calories in, so I would take every opportunity to get it done, whenever I could. I ended up getting through both bottles, but none of the cola shots. As I came into T2 I took one of the cola shot packets with me for the run. So, even though I was under my calorie goal, my power was also less than planned so I felt that I was covered.


I tried something new on the run at Arizona. Instead of starting with coke, I would start with a bottle of UCAN (2 servings) for the first hour. I froze my bottle so it was nice and cold. I could get a few sips out but then I had to add water in order to thaw it a bit. I was done with the UCAN after about an hour, after which I would stop every 5th aid station or so and refill the bottle with coke. I ate a few power bar cola shots whenever I felt like it (mile 13 onwards) and that was it. I was initially a bit concerned that the UCAN would be too slow to release, but it seemed to work quite well for me. I felt constant energy throughout the run, and the coke definitely gave a boost when it was needed in the latter part of the marathon.


High fat breakfast: definitely worked well for me. I’ll be doing this again for sure. Next time will drink more water up till race start.
Windy bike: will be experimenting with the Torhans vs my current “bottle between the bars”
Run: will definitely do the split approach of starting with UCAN then switching to coke. I also like the little hand strap of the camelbak bottle, better than running with just a bike bottle in hand. Maybe I’ll experiment with one of those “bottle holsters” – which I’ve avoided in the past because I don’t like having anything around my waist.

1 thought on “Ironman Arizona Nutrition Report

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