Nutrition & IM racing

Description of my approach to Ironman race nutrition.

Nutrition tapering

I consider racing nutrition to start long before the race itself. It takes quite some time for your body to adapt to using greater amounts of fat for fuel, so I believe the main training load must be done in lower carb state to initiate this adaptation. Based on my experience, it took me approx. 4-6 weeks to become more efficient in fat burning and then additional 4-6 week to roughly find my optimal carb intake range. After this period, your body becomes less dependent of carbs. After completing the major block of training for A race, I begin to taper 2-3 weeks before the event. This is the time for me to reduce the carb intake from 200 g per day to 150 g 2 weeks out and then to 100 g on penultimate week. I further reduce the carb intake to under 100g on the last 5 days in order to really amplify my reliance on fat as a fuel, so the performance drops quite substantially in the final week despite greatly reduced training load. I start to carbo-load on the evening on penultimate day, ingesting approx. 150 g of carbs, and then on the last day before the race, when I consume approx. 450 g of carbs. According to literature, one day of carb loading is enough to replenish all glycogen stores. And when compared to more traditional 3-day carb loading, it doesn’t offset the fat-burning mode back to greater carb-reliance. 

My carb intake in final 3 weeks before IM race

My carb intake in final 3 weeks before IM race

Race nutrition

On the morning of the race I eat 50 g carb breakfast and in the final minutes before the race start I consume 1 energy gel (25 g of carbs). On IM races I have two bottles with carb solution and one with water. The first bottle contains only 40g of carbs and is intended just for immediate hydration after the swim, if I need it. The main bulk of carbs is in other bottle, where I mix 300 g of carbs with water and salt. I use table sugar and maltodextrin in 2:1 ratio, which then gives me approx. 2:1 ratio of glucose to fructose. It has been shown in studies that absorption of multiple carbohydrates is quicker that absorption of single type carbohydrate. By using concentrated solution and plain water in separate bottles, it is easier for me to regulate carb intake and hydration, especially in hot races like Hawaii, where the water consumption is greater than the need for carbs. On the run, I rely on gels and / or coke. I consumed 4 gels in Lanzarote while drinking only water, while in Hawaii I had only 1 gel and drank coke on aid stations. It was probably the hot conditions that made me prefer diluted concentration of carbs in the coke more frequently than taking down larger amounts of carbs on fewer occasions.

So altogether I consumed approx. 370 g of carbs during the IM Hawaii and 470 g in Lanzarote. The difference of 100 g is due to smaller consumption of carbs on the bike, as I spend 40 minutes less on Hawaii bike course and I felt that I don’t need more carbs.

My carb intake during Ironman race day

My carb intake during Ironman race day

Overall, I think that greater care must be taken to avoid overstuffing yourself before and during the race. It’s really easy to get into the mainstream hype of “carbo-loading” and taking every single opportunity to gulp down carbs (just think Expo samples!). In the past I also struggled to hold back at carbo-loading, as I would often go to races with overfull stomach, causing me slight discomfort and reflux during swim that would often last into the first section on the bike. But when fat adapted, the amount of carbs needed before and during the race is far smaller, which also means lower chance of some kind of gastric distress. And of course better performance!

One thought on “Nutrition & IM racing

  1. Josh Shadle

    Wow, spot on article. Are you part of the runketo group on facebook? If your not, you need to join, i can invite you. I basically did this at my last half ironman, I went sub-threshold on the bike so i over did it big time, stupid. However, I only took gu’s on the bike and a gu and coke on the run. I should of bonked, but thankfully doing a keto diet for about 4 months really saved me. Ill check out the rest of your site. Good stuff!


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