If you’ve ever faded late in an Ironman, there’s a good chance fueling was the reason. Your body can only store a limited amount of carbohydrate, and once it’s gone, no amount of fitness will save the day. Ironman fueling is about keeping energy steady for hours, not just surviving the early miles.
How Many Carbs Per Hour during the IRONMAN Bike?
For most athletes, the ideal target is 80–100 grams of carbs per hour, especially during the bike leg. The Ironman bike is the best time to fuel because intensity is controlled and digestion is easier. Lighter or less experienced athletes may start closer to 80 grams, while trained athletes can often handle 100 grams or more. Dialing in carbs per hour on the bike is one of the biggest performance gains in long-course racing.
How Many Carbs Per Hour during the IRONMAN Run?
During the Ironman run, carb intake should be simple, consistent, and realistic. Most athletes do best aiming for 50–80 grams of carbs per hour, depending on body size, race intensity, and how well they fueled on the bike. Unlike the bike, digestion is harder while running, so liquid carbs, gels, or small frequent sips at aid stations tend to work best. The goal isn’t to “catch up” on calories, but to maintain blood sugar and slow fatigue as glycogen runs low. Athletes who start fueling early on the run and keep intake steady are far more likely to hold pace and avoid the late-race fade that defines so many Ironman marathons.
It’s important to understand that endurance fueling is trainable. You shouldn’t wait until race day to test Ironman bike nutrition. Use long rides to practice your intake, monitor stomach comfort, and see how your energy holds late in the session. Many athletes do better using multiple carb sources to improve absorption and reduce gut issues.
Finally, proper Ironman fueling isn’t just about the bike, it’s about protecting the run. Athletes who under-fuel early often pay for it in the final miles, even with conservative pacing. Start simple, fuel consistently, and build your carb intake gradually in training. When carbs per hour are right, Ironman racing becomes far more controlled and predictable.
Top Recommendations for Carb Fueling
1) Raw Endurance (3-4 Scoops per hour)
2) Tailwind (3-4 Scoops per hour)
4) First Endurance Regular Mix (great electrolyte count)
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