Nutrition for Ironman races
The complete fueling playbook for full distance triathlon events.
By Lotte
Ironman nutrition is the fourth discipline. Plan to consume 5,000-7,000 calories on race day, including 60-90g carbs/hour on the bike and 40-60g on the run. Have Plans A, B, and C — flexibility is essential.
Key takeaways
- 1You'll burn 8,000-10,000+ calories — nutrition determines your race outcome
- 2Carb-load 2-3 days before with 8-10g/kg body weight of carbohydrates
- 3Bike: 60-90g carbs/hour, set a timer to eat every 20-30 minutes
- 4Run: Switch to easily digestible sources — gels, cola, broth
- 5Practice your plan 8-10 times in training — nothing new on race day
In this article
The scale of fueling an Ironman
During an Ironman, you'll burn 8,000-10,000+ calories. You cannot replace all of them, but you need to consume 5,000-7,000 calories throughout the day including pre-race nutrition.
Nutrition is genuinely the fourth discipline at this distance. Get it wrong and no amount of fitness will save you.
Pre-race loading
Carb-load for 2-3 days before the race by increasing carbohydrate intake to 8-10g per kg of body weight. This maximizes glycogen stores.
Race morning: eat your practiced breakfast 3 hours before start — typically 600-800 calories of easily digestible carbohydrates.
Bike nutrition plan
Aim for 60-90g of carbohydrates per hour on the bike. Use a combination of sports drink in your bottles and solid foods in your pockets.
Set a timer to eat every 20-30 minutes rather than waiting until you're hungry. By the time you feel hungry, you're already behind.
Good bike leg foods: bars, gels, PB&J sandwiches, rice cakes, bananas.
Run nutrition plan
Continue consuming 40-60g of carbs per hour during the marathon. Switch to easily digestible sources — gels, flat cola, broth.
Walk through aid stations to eat and drink effectively. The 30 seconds spent walking saves stomach issues later.
Late in the marathon, solid food may not appeal. Cola and broth provide calories, sodium, and psychological comfort.
Contingency planning
Have backup nutrition in your special needs bags. Know what's available at aid stations as a fallback. If your stomach rebels, switch to small sips of cola and broth until it settles.
Flexibility is key. Have a Plan A, B, and C for nutrition.
Frequently asked questions
How many calories should I consume during an Ironman?
Aim for 60-90g of carbohydrates per hour on the bike (240-360 calories/hour) and 40-60g on the run (160-240 calories/hour). Total on-course intake is typically 3,000-4,500 calories including pre-race breakfast.
What if I feel sick during the race?
Slow down, switch to small sips of water or cola, and walk if needed. Nausea usually passes in 10-20 minutes. Resume eating with small amounts once your stomach settles. Cold cola and chicken broth are often the most tolerable options.