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Fueling for Ironman

Self-coaching notes

T-minus 25 days until my first Ironman, and in a typical last minute self-coaching attempt, I'm going to try to figure out if I'm fueling correctly. They say, nutrition is the 4th discipline of an Ironman, and my nutrition approach has been far from scientific.

I've bonked on a couple long bike rides and learned that I need to fuel more. Trying to save $2 here or there by eating less is stupid, and planning pit stops to re-up on fluids and foods on long rides is smart. I've also eaten too much before a run, and had stomach issues. Note to self: Don't eat +700 calories within 1.5 hours of a run.

It's a tricky balance between getting enough calories down, and tolerating the intake. It's an art and a science. So far, my approach has been all art and no science. Fueling and nutrition has definitely been present in my training. I feel like I have a pretty good grasp on fueling by feel, and what I like or don't like to consume. But I've also never done a full Ironman before. So my goal in this post is to bring some science into the self-coaching program, and dive into the hard numbers.

Fueling for Endurance

About a year ago, I attended a Fueling For Endurance webinar put on by Jesse Kropelnicki from Fieldwork Nutrition. It was jam packed with good info, and I learned a lot. But to be honest, the high level theoretical stuff resonated with me more than the nitty gritty details.The details - lean body weight, carbohydrate intake, and milligrams of sodium - sound like a foreign language to me. I am going to force myself to dive into the nitty gritty in a second, but first I want to touch on Jesse's high level approach.

Race outcome is the factor of these 5 cornerstones...


(1) Training

(2) Nutrition/Recovery


(3) Race Fueling

(4) Pacing


(5) Mental Fitness, which applies to both preparation and execution. It includes your love of the sport and the process, waking up early and getting after it, and good self talk on race day.

Training and race day are fun, while the nutrition, recovery and fueling portions usually not as fun. Case in point, I've logged 128 hours of training so far this year and enjoyed most of it, but I'm only now spending the time diving into my fueling approach.

One thing worth noting that Jesse changed my mind on in that webinar was fasted workouts. At the time, I was doing a lot of fasted runs first thing in the morning, and could pump out 9-12 miles without eating, no problem. It was convenient not having to plan what to eat before or wake up early to let it digest. And in my mind, I assumed fasted workouts were a good thing, assuming that I was burning fat instead of glycogen, and working on metabolic efficiency (*see side note below).

But Jesse changed my perspective, reframing the "fasted" workout as "starvation" workouts, and explained potential risks. Especially for someone like me, with low body fat % and BMI already, there could be catabolic effects where my body breaks down lean muscle mass for fuel (not good). If my workouts are limited by a lack of fuel, how can that help me increase fitness and performance? And most important, as I was starting to ramp up training miles in preparation for ultramarathons, I was missing an opportunity to train my digestive system to handle the fueling. The gut needs to be trained to absorb the fuel, just as the muscloskeletal system need to be trained to handle the distance. A-ha moment!

So from that point forward, I started experimenting with different pre-workout meals, and kept a log to document what I ate and how I felt. I also experimented with different gels for fueling on my runs. This experimentation has been the extent to my fueling discipline.

*Side Note: In Training for the Uphill Athlete, the most comprehensive book I've read on the topic of endurance training, the authors say that becoming fat adapted (burning fat instead of glycogen) is one of the simplest and highly advantageous training prescriptions. The best way to do this is with long duration, low-intensity training sessions. They say that you can also boost your fat adaptation by doing "some" of your aerobic-capacity building workouts in a fasted state, and by modifying your diet to low carbohydrates and higher in fat. However, they also say that if you do more than 12 hours of weekly training, diet modifications will have less of an effect and the low-intensity training volume will be ample stimulus for fat adaptation.

Pre-Workout Fueling Recommendations -

  • Hydrate - 16-24oz of fluids within 2 hours
  • Eat 25-60g of easy cabs within 1 hour
  • Keep the fat and fiber (harder to digest) low for runs especially

Now fast forward a year and I have an Ironman 70.3 under my belt. I'm pretty sure that my fueling sucked during my 70.3. I was happy with my overall time (hit my sub-6 goal), but my run split was UGLY AS HELL. I barely broke the 2 hour mark, and felt sluggish from the minute I got off the bike. Granted, I had only started cycling 1 month before was was undertrained, and it was a hot 95 degree race day in Whistler (looking around I was not the only one out there struggling). But I also think I didn't take fueling seriously enough, and underestimated how much I needed to intake as a result.

Now that I'm gearing up for a full Ironman in 25 days (lol), I'm about to dive into the nitty gritty and try and self-coach a more solid race day fueling plan.

How to Fuel for Ironman

So let's start with this article from the official Ironman website - How Do I Fuel For Ironman? 

"As a general rule of thumb, endurance athletes should aim to eat 60-90 grams of carbohydrate per hour during IRONMAN events, with athletes typically able to consume more calories and fluids during the bike leg and fewer calories during the run portion of the event... In hot and humid races, athletes may benefit from a sodium intake of 500-1,000 milligrams per hour."

But since I was smart enough to attend Jesse's webinar last year (although I was not smart enough to apply it until now), I can go a little deeper than the Ironman "general rule of thumb."

Here is what Jesse prescribes -

  • Carb loading - for an Ironman, start at lunch 2 days before, with 2.7 X body weight. The day before race day should be 4.5 X body weight, with breakfast being biggest meal and taper meals throughout the rest of the day with something light and close to bed time. (For 70.3, its 2.4 and 4.5)
  • Race Day Breakfast - 2.5-3 hours before, 1.25 grams x lean body weight for carbohydrates (CHO). For 70.3 drop down to 1X. Ideally, something low glycemic, hydrating, sodium rich, moderate protein, low in fat and fiber.
  • The Big Three for Training/Racing - Fluids, Carbohydrates, Sodium
  • Rule of thumb for fluids - Drink every 10 min, pee every 2 hours
  • Consume 25g of CHO every 30-45 min depending on body weight. On the bike, CHO intake 5/8 X lean body weight. 50% of that for the run.
  • Sodium intake 600-1800mg per hour, depending on sweat rate
  • Optional - build caffeine throughout the day, 1-2X body weight in mg total for the day

My Magic Numbers

My body weight is around 140 lbs and 7% body fat, making my lean body weight around 130. Let's do the math to find my magic numbers...

  • Carb loading - 2 days before 378g lunch+dinner. Day before 630g breakfast+lunch+dinner.
  • Race day breakfast - 162g CHO
  • On the bike - 80g CHO/hr. (6.5 hr bike = 520g)
  • One the run - 40g CHO/hr. (4 hr run = 160g)
  • Total estimated CHO intake over 10.5 hrs on bike+run legs is 680g. That's about 65g per hour, which is also in range for what the Ironman website recommends as a general rule of thumb.

My Fueling From 2 Brick Workouts

Now, I will break down 2 brick workouts I did where I tracked my numbers to see where I am at compared to the above recommendations.

Brick 1 - April 2nd, 2019

54 mile bike, 3 hr 14 min. 6 mile run, 51 min. Total duration - 4 hr 5 min.

  • Nuun Electrolyte - 10 cals, 4g CHO, 360mg sodium
  • CarboPro - 150 cals, 37g CHO
  • ClifBar - 260 cals, 42g CHO, 220mg sodium
  • LaraBar - 220 cals, 28g CHO, 5mg sodium
  • LaraBar - 190 cals, 27g CHO
  • Spring gel - 100 cals, 17g CHO, 60mg sodium
    • Totals - 920 cals, 155g CHO, 645mg sodium
    • Per hour - 230 cals, 39g CHO, 161mg sodium

Brick 2 - April 12, 2019

100 mile bike, 5 hr 55 min. 3 mile run, 24 min. Total duration - 6 hr 20 min.

  • Nuun Electrolyte X2 - 20 cals, 8g CHO, 720 sodium
  • CarboPro - 400 cals, 100g CHO
  • ClifBar X3 - 780 cals, 126g CHO, 660mg sodium
  • LaraBar X2 - 440 cals, 46g CHO, 170mg sodium
  • Muir gel - 115 cals, 25g CHO, 100 sodium 
  • 1/2 cup trail mix - 140 cals, 15g CHO, 5mg sodium
  • 3X cuties - 120 cals, 25g CHO
    • Totals - 2015 cals, 345g CHO, 1655mg sodium
    • Per hour - 318 cals, 54.5g CHO, 261mg sodium

During both workouts, I felt pretty good - stable energy, no GI issues. Also to note, the weather on both days was sunny but cool, with a pretty low sweat rate.

My Takeaways

I will admit, April 2nd was the first time I looked at the nutrition labels of the products I used to see what I was actually consuming. The first thing I realized is that ClifBars are far superior than LaraBars for fuel, as LaraBars have 35% less CHO and no sodium.

During my century brick on April 12, I increased my CarboPro intake since those are very easy calories to consume, and opted for more ClifBars. This helped my CHO intake reach 54.5g per hour. If racing requires 65g CHO per hour, it seems like 55g per hour for a training brick is sufficient, although I could benefit from training my gut to take in the full 65g. Either way, I had good energy through the workout, all considering.

My sodium intake, at 260mg per hour, is far below the recommended the 500-1000mg or 600-1800mg per hour that is recommended above. My justification for this is a couple things - (1) I don't sweat a lot in general, (2) I especially don't sweat a lot on the bike with all the cool air blowing on me (3) both those days were pretty cool days. I'd assume that since I sweat a lot more on the run, I might want to up my sodium intake during the marathon leg of the Ironman. And of course, if it's a hot day, like the 95 degrees it was for my 70.3 in Whistler last summer, I need to get a lot more sodium in.

Potential Race Day Fueling Plan

4am race day breakfast (2hr40min before swim start) - target 162g CHO.

  • 1cup of muesli - 84g
  • Smoothie - 57g (Fieldwork Primo Mix 18g, banana 27g, strawberries 6g, coconut water 6g)
  • Cordyceps drink - 4g
  • 6am Spring Energy gel - 17g
  • TOTAL: 162g

Bike fueling - target 80g CHO per hour.

  • ClifBar every 40 min (3 every 2 hours, 10 total) - 63g per hour 
  • Nuun Endurance drink - 16g per hour, which is 1 20oz bottle per hour (6.5 total)
  • Total - 79g per hour
  • Sodium - 275mg + 380mg = 655mg per hour

Run fueling - target 40g CHO per hour

  • Spring Energy gel every 30 min (7 total) - 34g per hour (also 120mg sodium/hr)
  • Plus sports drink at aid stations will bring number close to 40g CHO and increase electrolytes as well

Here is another great article from Jesse, on the Fieldwork Nutrition blog on race fueling - 10 Nutrition Do's and Don'ts for Racing the Kona IM Championships

Dress Rehearsal - April 22, 2019

After I wrote the above, I went out for a 4 hour (1+2+1) dress rehearsal to test everything out. I planned to wear exactly what I would wear race day, fuel exactly how I planned above, and push it at about 95% race day effort.

  • Swim - 3200 yds, 55 min, 1:43/100yd. Projected 1h10m IM swim leg.
  • Bike - 35.5 miles, 2h3m, 17.3 mph. Projected 6h30m IM bike leg.
  • Run - 8.1 miles, 1h1m, 7:31 pace. That projects about a 3h16m marathon which won't happen, so hoping for a 3h45m IM run leg.
  • Total - Projecting between 11h30m to 12hr IM time on a good day.

Fueling - 1 Spring Energy before the swim. 1 Clifbar in T1, and 2 more on the bike, plus 40oz of fluids on the bike with CarboPro in one bottle and Nuun Electrolyte mix with caffeine in the other.

Fueling is where things got interesting. Had the pre-race breakfast about 2.5 hours before, then a Spring Energy right before the swim, and everything felt good up to this point. When I was in T1, I ate my first Clifbar and then got on my bike. At 40min in, my stomach felt full still from the1st Clifbar, so I waited an extra 5 min and ate my 2nd Clifbar at the 45min mark. This made me feel very full, and on top of the fluids, made me very bloated. Being crouched over in aero position was uncomfortable. The GI issues did not go away, and at the 1h30m mark on the bike, I ate my 3rd Clifbar to try and stay on schedule. I got off the bike VERY full, and for the first 5-6 miles of the run had stomach issues. I was unable to fuel on the run at all. Despite the stomach issues though, everything else felt very strong.

My plan for my 2nd dress rehearsal is to not eat my first Clifbar in T1, but instead get on my bike, and only take in calories once I feel like I'm ready, sometime within the first 45min on the bike hopefully. I'll also wait to take in any fluids until I feel necessary. From then on, I'll decide to eat again between 45min-1hr depending on how I feel. What I think might happen is that for the first 2-3 hours of the bike I might only eat every 1hr, and then for the next 3-4 hours reduce that to 45min. This is more similar to how I fueled during my long brick workouts.

Either way, I learned that forcing the fuel in based on what's recommended doesn't work, and that I should combine the recommendations with how I feel and how I trained. I also learned that dress rehearsals are key, and I'm glad that I'm making these mistakes in training a few weeks before race day.

Notes on dress rehearsal 2 coming soon...

*Dress rehearsal 2 never happened, my bike was in the shop 1 week longer than expected due to parts on back order.

Race Day Fueling - Ironman Santa Rosa

Ironman Santa Rosa is now complete! It was an amazing experience, and I will write a full race recap on it, but for now I want to document my race day fueling to keep all of this in one organized post. Overall, I feel like I fueled well, and my race was not limited by nutrition.

  • Pre-race Breakfast: 160g CHO, 1082 calories
  • Bike leg: 424g CHO, 2028 calories (65g CHO and 312 cals per hour) - about 100oz of fluids, and went pee about 5 times on the bike.
  • Run leg: 185g CHO, 1000 calories (41g CHO and 222 calories per hour) - not sure how much fluids but went pee 3 times on the run.

Race day breakfast was exactly as planned, a cup of Seven Sunday's muesli and a Fieldwork Nutrition smoothie about 2 h 40 min before gun time, a cordyceps mushroom elixir, and a Spring energy gel about 15 min before gun time, for a total of about 160g CHO and 1082 calories. It digested well, and I felt great during the swim and the start of the bike.

On the bike, I started the day with 2 20oz bottles of CarboPro, and decided to do that instead of Nuun Endurance because I thought that I would want the carbs versus the electrolytes early on. The morning was cold (mid-50s) and I didn't anticipate myself sweating all that much for the 1st half of the bike or needing electrolytes. I'm especially happy with that decision because for some reason the Clifbars just weren't going down all that easily, and I was eating them a half at a time, or less, which is something I never did in training. I was halfway through the bike at exactly 3 hours in, and had consumed 40oz of fluids with CarboPro, 100g CHO and 400 cals, and 2 Clifbars, 90g CHO and 500 cals, for 190g CHO and 900 cals (63g CHO and 300 cals per hour).

On the second half of the bike, I had 2 more Clifbars (84g CHO, 520 cals), 3 bottles (60oz of fluids) of Gatorade Endurance (110g CHO and 450 cals), and 1.5 bananas (40g CHO and 158 cals). I switched to bananas because I couldn't eat more Clifbars. That brings the totals during the 3.5 hour duration of the 2nd half of the bike leg - 234g CHO and 1128 calories, 67g CHO and 322 cals per hour.

I got off the bike feeling great, legs were springy, and I felt hydrated and fueled. I had half a bottle of CarboPro in T2 before heading out to the run, about 25g CHO and 100 cals. I had a Spring Energy gel around the 35 min mark, and another one around the 1:15 mark. Then the plan just went out the window, and I started walking aid stations and eating/drinking whatever sounded good. Over the course of the rest of the run, I had 2 more Springs, maybe 3, I started to lose track. 4 total would have been 60g CHO and 470 cals. I drank a bunch of water and Gatorade Endurance, had coke once, and ate a few bananas, oranges and handful of pretzels when real food started to sound better than gels which probably totaled another 100g CHO and 430 cals. Total for the 4.5 hour run was probably around 185g CHO and 1000 calories, 41g CHO and 222 calories per hour.

Overall learning lessons

  • Pre-race breakfast was perfect, and I will want to replicate that for future races.
  • Bike fueling - I had 5 different Clifbar flavors which I thought would be enough variety, but it wasn't. I need to find a new bar to mix things up with, maybe Larabar, or Picky Bars. And once I realized the Clifbars weren't really working, drinking more calories and eating bananas from the aid stations seemed to work great as a backup plan.
  • Run fueling - I'm not sure what I learned yet related to run fueling. My run ugly, but I'm not sure if that was related to fueling at all, or training. I think it was training, and not fueling.
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