The Carbohydrate Revolution: How We Got Here

The evolution of endurance fueling recommendations tells a fascinating story of scientific discovery outpacing itself. Before 2010, the conventional wisdom capped carbohydrate intake at 60 grams per hour, based on what researchers believed was the maximum our intestines could absorb.

Everything changed with the discovery of multiple transportable carbohydrates. Scientists found that combining glucose and fructose—which use different absorption pathways—could dramatically increase the body's ability to process carbs during exercise. This breakthrough pushed recommendations from 60 grams to the current 60-90 grams per hour for events lasting 2.5 hours or longer.

But elite athletes didn't stop there. Recent evidence from the Tour de France, Giro d'Italia, and now Ironman World Championships suggests that 90-120 grams per hour might be optimal for peak performance. Today's Ironman pros are consuming 120-180+ grams hourly, essentially beta-testing the future of endurance nutrition.

The gap between research and practice has never been wider. While scientific studies struggle to keep pace with rapidly evolving protocols, elite athletes are conducting real-world experiments at the highest level of competition—and the results speak for themselves.

Inside the Pros' Fuel Tanks: What Champions Actually Eat

The Men's Strategies (Nice, France)

The Women's Strategies (Kona, Hawaii)

The Science Behind Extreme Fueling

Understanding why these extreme strategies work requires grasping the fundamental relationship between exercise intensity and fuel utilization. As intensity increases, carbohydrate becomes the dominant fuel source. While recreational athletes might burn a 50/50 mix of fat and carbs, elite athletes at race pace are running almost entirely on carbohydrates.

The Physiology of High-Carb Fueling

Professional Ironman athletes sustain intensities that demand massive carbohydrate oxidation rates—often 3-4 grams per minute. Without adequate fueling, their bodies would rapidly deplete glycogen stores, leading to dramatic performance decline within hours.

Gut training is the secret weapon that makes high intake possible. Like training any other system, the digestive tract adapts to regular high-carb exposure by:

• Increasing glucose and fructose transporter proteins
• Enhancing gastric emptying rates
• Improving intestinal absorption capacity
• Reducing GI distress at higher intake levels

This adaptation takes months of consistent training and forms the foundation of every successful high-carb strategy.

The Role of Multiple Carb Sources

Modern fueling strategies rely heavily on glucose-fructose combinations to maximize absorption. Glucose uses SGLT1 transporters, while fructose uses GLUT5 transporters—by utilizing both pathways simultaneously, athletes can exceed the ~60-gram hourly limit of single-source carbs.

The most effective ratios appear to be:

• 2:1 glucose to fructose (most common)
• Maltodextrin-fructose combinations
• Glucose-sucrose-fructose blends

Metabolic Testing: The Foundation

Every elite fueling strategy begins with metabolic testing—laboratory analysis that measures exactly how much carb and fat an athlete burns at different intensities. This data reveals:

• Personal carb oxidation rates at race pace
• Optimal fueling zones for different efforts
• Individual responses to various carb sources
• Gut tolerance thresholds

Without this baseline data, high-carb strategies become dangerous guesswork.

Age-Group Reality Check: Why More Isn't Always Better

Before you start planning your own 180-gram hourly intake, consider this crucial reality: age-group athletes race at fundamentally different intensities than professionals.

The Intensity Gap

Most age-group athletes complete Ironman at 60-75% of their maximum sustainable power, while pros race at 85-90%. This intensity difference dramatically impacts carbohydrate requirements:

• Lower intensity = higher fat oxidation
• Longer race time = different fueling timeline
• Less trained digestive system = lower absorption capacity

For most age-groupers, consuming 70-90 grams per hour provides optimal performance without the risks associated with extreme intake.

The "Train Low, Race High" Trap

Susan Kitchen identifies a common age-group mistake: "Far too often, I see athletes who underfuel during training but plan to fuel with 90-plus grams per hour on race day." This "train low, race high" approach is like attempting an Ironman without proper training—it rarely works.

Your gut needs training just like your muscles. If you can't comfortably consume and process 90 grams per hour during training, you certainly can't do it under race stress.

Lifestyle Reality

Professional athletes structure their entire lives around optimization. Their daily routines include:

• 8-12 grams of carbs per kilogram of body weight
• Multiple daily training sessions with fueling practice
• Regular metabolic testing and strategy refinement
• Professional nutrition and coaching support

Age-group athletes juggle careers, families, and other commitments. While admirable, this lifestyle difference means what works for pros often isn't practical or necessary for recreational competitors.

Risk vs. Reward Analysis

High-carb fueling carries real risks:

• GI distress if gut isn't properly trained
• Bonking if fueling plan fails mid-race
• Overcomplication of an already challenging event
• Performance anxiety from untested strategies

For age-groupers, the performance gain from extreme fueling rarely justifies these risks. A conservative, well-practiced strategy typically produces better results than an aggressive, untested approach.

Building Your Personal Fueling Strategy

Creating an effective fueling plan requires systematic development over months, not days. Here's how to approach it intelligently:

Step 1: Assess Your Current Capacity

• How many grams can you comfortably consume per hour?
• Which products work best for your gut?
• At what point do you experience GI issues?
• How does heat affect your tolerance?

Step 2: Choose Appropriate Targets

• Conservative approach: 60-70 grams per hour
• Moderate approach: 70-90 grams per hour
• Aggressive approach: 90+ grams per hour (requires extensive preparation)

Remember: it's better to slightly underfuel than to blow up from overconsumption.

Step 3: Progressive Gut Training

If you want to increase intake, follow a systematic progression:

Weeks 1-4: Establish baseline tolerance

• Practice current intake during long sessions
• Identify preferred products and timing
• Note any GI issues or patterns

Weeks 5-8: Gradual increase

• Add 10-15 grams per hour to long sessions
• Monitor gut response and adjust accordingly
• Practice race-day timing and products

Weeks 9-12: Refinement and testing

• Simulate race conditions during key workouts
• Practice backup plans and contingencies
• Fine-tune product combinations and timing

Step 4: Product Selection and Combinations

Choose products that combine glucose and fructose for optimal absorption. Consider using quality electrolyte supplements to maintain hydration alongside your carb intake:

• Drink mixes: Look for maltodextrin-fructose or glucose-fructose blends
• Gels: Rotate between different brands to prevent flavor fatigue
• Solid foods: Consider for ultra-distance events or personal preference
• Electrolytes: Don't forget sodium, especially in hot conditions - magnesium and potassium supplements can help prevent cramping

Step 5: Backup Planning

• Dropped bottles: Extra gels or course nutrition
• GI distress: Simplified fueling protocol
• Heat stress: Increased fluid, reduced carbs
• Longer-than-expected finish: Extended fueling timeline

When to Consider Professional Help

• Consider working with a sports dietitian if you consistently struggle with fueling during long training
• Want to optimize performance through metabolic testing
• Experience frequent GI issues during exercise
• Are targeting highly competitive age-group placement

Key Takeaways and Action Steps

The carbohydrate revolution at the 2025 Ironman World Championships offers valuable insights, but the key lesson isn't about consuming more carbs—it's about systematic preparation and individual optimization.

Essential Principles

1. Pros' extreme fueling requires extreme preparation that most age-groupers can't replicate
2. Individual testing trumps copying elite strategies regardless of how impressive they seem
3. Consistent practice matters more than peak numbers for race-day success
4. Conservative, well-executed plans typically outperform aggressive, untested strategies

Your Next Steps

1. Assess your current fueling capacity during the next long training session
2. Choose realistic carb targets based on your race intensity and experience
3. Begin systematic gut training if you want to increase intake
4. Test and refine your strategy over multiple training cycles before race day

The Future of Fueling

As research catches up to elite practice, expect continued evolution in fueling recommendations. However, the fundamentals remain constant: individual testing, progressive training, and systematic preparation will always matter more than copying someone else's numbers.

Start developing your personalized fueling strategy now. Your next race performance depends on months of preparation, not race-day heroics. The pros didn't stumble upon their 180-gram strategies overnight—they built them through systematic work that you can adapt to your own goals and capabilities.

Remember: the best fueling plan isn't the most extreme one. It's the one you can execute flawlessly when it matters most.