Carb Loading for Female Endurance Athletes: What New Ironman Research Reveals

In Episode 163 of the Find Your Edge Podcast, registered dietitian and triathlon coach Chris Newport reviews a 2026 study of 27 women at the IRONMAN World Championship. Only 26% met carbohydrate loading guidelines of 8-12 g/kg, higher carb intake was linked to faster finishes, and higher fiber to more GI symptoms. Chris explains how to practice carb loading, train your gut and plan race-day logistics.

Key takeaways

• Only 26% (6 of 23) of women studied at IRONMAN Worlds met carb loading guidelines, averaging about 6.4 g of carbohydrate per kg of body weight instead of 8-12.
• Higher carbohydrate intake before the race was associated with faster finish times.
• Higher fiber intake before the race was strongly associated with worse GI symptoms.
• Knowing the guidelines wasn’t enough. Mindset, race nerves, travel and logistics shaped what athletes actually ate.
• Start gut training once your workouts reach 90 minutes or more, so race week is a repeat of what you’ve already practiced.

“My race is this weekend. What should I eat?”

I get this call ALL the time. You’ve done the long rides and long runs, you’ve put in the work… and suddenly it’s race week and you realize you haven’t quite figured out your nutrition. If that’s you, you’re not alone.

The honest answer is that race week nutrition starts months earlier, while you’re training your body AND your gut. New research on female endurance athletes shows exactly why.

What did the study on female Ironman athletes find?

Researchers followed 27 women racing the 2024 IRONMAN World Championship using questionnaires, 48-hour food diaries and interviews before and after the race. Of the 23 athletes with complete food data, only 6 (26%) met carbohydrate loading guidelines. The average intake was about 6.4 g of carbohydrate per kilogram of body weight, well below the recommended 8-12 g/kg.

Two other findings stood out. Women who ate more carbohydrate tended to finish faster (an association, not proof of cause, but consistent with what we know about carbs and endurance performance). And higher fiber intake was strongly linked to more GI symptoms.

How many carbs do you need to carb load?

Current guidelines recommend 8-12 grams of carbohydrate per kilogram of body weight per day for 1-3 days before a long endurance race. Here’s the quick math:

1. Divide your weight in pounds by 2.2 to get kilograms.
2. Multiply by 10 (the middle of the range) to get grams of carbohydrate per day.
3. Multiply that by 4 to see the calories from carbohydrate alone.

For a 132-pound (60 kg) athlete, that’s about 600 grams of carbohydrate and roughly 2,400 calories from carbs in a single day. That surprises a lot of athletes, especially women who have spent years thinking of carbs as something to limit. It’s also why carb loading needs to be practiced, not attempted for the first time the week of your Ironman. (I once worked with an athlete who tried exactly that. It did not go well.)

Why can fiber cause GI problems before a race?

For everyday health, we encourage plenty of fiber, vegetables and whole grains. But right before a long race, that same fiber can sit heavy and trigger bloating, cramping or bathroom stops. Race nutrition isn’t always the same as your everyday healthy eating, and it’s okay to temporarily shift toward lower-fiber carbohydrate sources in the final days.

Why isn’t knowing what to eat enough?

This was my favorite part of the study. Athletes who saw themselves as “competers” tended to plan carefully and follow their strategy. Athletes who saw themselves as “completers” took a more intuitive approach. As one said, “I’m not fast, you know. I don’t need all that sugar.”

Then add real life: travel, flight delays, a hotel without your usual foods, athlete check-in, and race nerves that make you lose your appetite. A plan that looks simple at home gets complicated fast.

One athlete in the study summed it up beautifully: “Why would you not want to set yourself up for the most success, or at least for a good experience?” You don’t need to be chasing a podium to benefit from a practiced plan.

How many carbs are right for YOU?

The guidelines are a starting point, not a one-size-fits-all rule. Your health matters too. If you have gout or high uric acid, high-fructose fueling products may not be your friend. If your A1C is creeping up, or you’re managing PCOS or type 1 diabetes, we look at the types and timing of carbohydrates that support both blood sugar and performance. And if you’ve been underfueling (very common in female athletes), jumping straight to 10 g/kg can feel physically and emotionally overwhelming. Sometimes we start at 3, 4 or 5 g/kg and build from there.

When should you start training your gut?

Start as soon as your workouts reach 90 minutes or longer. That might be two, three or eight months before your event. Use your long sessions as your nutrition lab:

• Practice the foods, drinks and gels you’ll use on race day, and research what the race provides.
• Build your carbohydrate intake gradually if your gut is sensitive.
• Practice your carb load before a long training day (2-3 days of mostly carbohydrate, then very light training).
• Practice the skills: grabbing bottles, opening gels, aid station handoffs.
• Plan your logistics: how much can you carry, and where will you refill?

Want to test it? Try your own experiment: race a 10K or sprint triathlon with and without a practiced carb load in similar conditions, and compare.

Don’t forget hydration

Your carbohydrate needs stay fairly steady on race day, but your fluid and sodium needs change with heat, humidity and intensity. Knowing your sweat rate is the only way to get close. That’s where our Fueling & Hydration Test and the Hydration Edge app come in: you get your personal starting point, then log sessions to learn how your needs change.

Your challenge

After your next long session, don’t just look at pace, power or heart rate. Ask yourself: Did I execute my nutrition plan? What worked, what didn’t, and what can I make easier next time? Jot it in TrainingPeaks or the Hydration Edge app. The goal is to reach your start line with fewer unanswered questions and more confidence in the work you’ve already done.

“Race-day nutrition isn’t just a calorie problem. It’s a behavioral, psychological and logistical one.” Coach Chris Newport

🎧 Listen above or watch on YouTube.

Related episodes

• How I Developed a Personalized Race Fueling Plan That Actually Works (Ep 95): https://www.theenduranceedge.com/how-i-developed-a-personalized-race-fueling-plan-that-actually-works/
• How to Prevent GI Distress in Endurance Athletes (Ep 105): https://www.theenduranceedge.com/how-to-prevent-gi-distress-in-endurance-athletes/
• Race Day Nutrition for Endurance Athletes (Ep 92): https://www.theenduranceedge.com/race-day-nutrition-for-endurance-athletes/

Stop guessing on race day

Our Fueling & Hydration Test measures your calorie, carbohydrate, fluid and electrolyte needs so you can build a race plan around YOUR body, not someone else’s. Then practice it with the Hydration Edge app.

Book My Metabolic & Sweat Test:
https://www.theenduranceedge.com/sweat-and-metabolic-vo2max-testing/

Short on time before race day?
Book a 30-minute Quick Start consult:
https://www.theenduranceedge.com/sports-nutrition-for-performance-longevity/

About the host: Chris Newport, MS, RDN, LDN, EP, CISSN, is the founder and head coach of The Endurance Edge in Cary, NC. She is a registered dietitian, exercise physiologist, certified sports nutritionist and triathlete who helps endurance athletes stop guessing about their training, nutrition and long-term health.

Research cited: From Intention to Execution: Pre-Race Nutrition Behaviours, Influences, and Performance Outcomes in Female Endurance Athletes at the IRONMAN World Championships. European Journal of Sport Science, 2026. https://onlinelibrary.wiley.com/doi/10.1002/ejsc.70193

FAQs

How many carbs should I eat to carb load for an Ironman?

Current guidelines recommend 8-12 grams of carbohydrate per kilogram of body weight per day for 1-3 days before a long endurance race. Divide your weight in pounds by 2.2, then multiply by 8-12. Practice this in training first, especially if you usually eat fewer carbohydrates.

Do female endurance athletes carb load enough?

Often not. In a 2026 study of women at the IRONMAN World Championship, only 26% met carb loading guidelines, averaging about 6.4 g/kg. Travel, race nerves and concerns about bloating or weight influenced what they ate.

Should I eat less fiber before a race?

Many athletes benefit from lowering fiber in the final 1-2 days before a long race. In the study, higher fiber intake was strongly associated with more GI symptoms. Shift to easy-to-digest carbohydrates and test this before a long training day.

When should I start gut training?

Start once your workouts reach about 90 minutes or longer, which is often 2-6 months before your event. Practice the exact foods, drinks and gels you plan to use, and build your intake gradually if your gut is sensitive.

Is carb loading worth it if I just want to finish?

Yes. You don’t have to be chasing a podium to benefit. A practiced fueling plan helps you feel stronger, avoid GI issues and enjoy the race more, whatever your goal.