"Carb-Loading Before a Race Is Non-Negotiable: Or Is It?"

Introduction: The Carb-Loading Commandment

For decades, carb-loading has been hailed as the golden rule for endurance athletes. Runners are told to stock up on pasta, rice, and bread in the days leading up to a race, with the promise of maximized glycogen stores and peak performance. But is this age-old ritual truly necessary—or is it an overhyped tradition that often causes more harm than good?

The truth? Carb-loading has its place, but it’s not a universal requirement. Depending on your race distance, training adaptations, and fueling strategies, blindly following the carb-loading mantra might not only be unnecessary but also counterproductive. Let’s take a closer look at the science behind carb-loading and when (or if) it’s worth the effort.

The Science of Carb-Loading

1. What Is Carb-Loading?
   Carb-loading, or carbohydrate supercompensation, involves consuming high amounts of carbohydrates (7-12 grams per kilogram of body weight) in the 1-3 days leading up to a race. The goal is to saturate glycogen stores in the muscles and liver, ensuring you have ample energy for prolonged efforts.
2. Why Glycogen Matters
   Glycogen is your body’s primary fuel source during high-intensity or long-duration exercise. When glycogen stores deplete, runners hit "the wall"—a dramatic drop in energy and performance.
3. Does It Work?
   For endurance events lasting 90 minutes or longer, studies consistently show that carb-loading can:

• Increase time to exhaustion.
• Delay the onset of fatigue.
• Enhance performance by 2-3%.

For shorter races, the benefits are minimal or nonexistent. Sprinting, 5Ks, or even 10Ks rely more on muscle phosphates and less on glycogen, making carb-loading largely irrelevant.

When Carb-Loading Works—and When It Doesn’t

1. Marathon or Ultra-Distance Events

Carb-loading is most beneficial for races lasting 90 minutes or more at moderate-to-high intensity. In these scenarios, your body’s glycogen stores are likely to be fully depleted without strategic fueling.

2. Shorter Races (5K to 10K)

For shorter races, your glycogen stores are unlikely to run out during the event. Instead of carb-loading, focus on eating a balanced diet that supports optimal energy and recovery.

3. Runners on Low-Carb Diets

For athletes following ketogenic or low-carb diets, fat adaptation minimizes reliance on glycogen. Carb-loading may offer little benefit in these cases, as fat becomes the primary fuel source during exercise.

4. Poor Execution Can Backfire

Carb-loading done incorrectly often causes:

• Weight gain: Every gram of glycogen stored retains 3 grams of water, potentially leading to bloating and sluggishness.
• Gastrointestinal distress: Overloading on fiber-rich or unfamiliar foods can disrupt digestion.
• Overeating: Consuming too many calories overall can leave runners feeling heavy and lethargic.

Common Carb-Loading Mistakes

1. Starting Too Early
   Some runners begin carb-loading a week before the race, leading to unnecessary calorie surpluses and weight gain. The effective window is 1-3 days before the event.
2. Overloading Without Adjusting Training
   Carb-loading is effective after a taper period. Consuming extra carbs while still maintaining high mileage won’t maximize glycogen stores.
3. Ignoring Protein and Fat
   Carb-loading doesn’t mean neglecting other macronutrients. Protein aids recovery, and fats help balance caloric intake without overloading the stomach.
4. Choosing the Wrong Carbs
   Complex carbs (e.g., whole grains) are often too fiber-heavy for effective carb-loading. Opt for simple, easily digestible options like white rice, pasta, or potatoes.

Alternatives to Traditional Carb-Loading

1. Fat Adaptation
   Some runners train their bodies to burn fat more efficiently, reducing dependence on glycogen. This approach involves lower-carb diets during training and strategic reintroduction of carbs closer to race day.
2. Carb Periodization
   Instead of a massive carb influx before a race, this method involves alternating low- and high-carb days during training to optimize fuel use.
3. Race-Day Fueling
   For shorter races or less intense efforts, pre-race meals and mid-race fueling (e.g., energy gels) can provide sufficient energy without full-scale carb-loading.
4. Modified Loading
   For those prone to GI distress or weight gain, a moderate increase in carbs (4-6 grams per kilogram of body weight) may offer similar benefits without the risks.

How to Carb-Load Properly (When It’s Needed)

1. Know Your Numbers
   Aim for 7-12 grams of carbs per kilogram of body weight daily for 1-3 days before the race. For a 70 kg runner, this translates to 490-840 grams of carbs per day.
2. Choose Smart Carbs
   Stick to low-fiber, easily digestible options like:

• White rice or pasta.
• Potatoes.
• Bread.
• Low-fiber cereals.
• Fruit juices or sports drinks.

1. Pair with Protein and Fats
   Balance carb-rich meals with lean protein (e.g., chicken or fish) and healthy fats (e.g., olive oil or avocado) to support digestion and satiety.
2. Avoid Last-Minute Binges
   Your pre-race dinner should be carb-focused but not excessively large. Overeating the night before can lead to discomfort on race morning.
3. Hydrate Strategically
   Glycogen binds to water, so staying hydrated is essential during carb-loading. Avoid sugary sodas or juices that can cause spikes and crashes.

Case Studies: Runners Who Broke the Carb-Loading Mold

1. Zach Bitter: The Low-Carb Ultra Runner

Zach Bitter, a world-record-holding ultrarunner, relies on a low-carb, high-fat (LCHF) diet to fuel his races. By training his body to burn fat efficiently, he minimizes glycogen depletion and skips the traditional carb-loading protocol altogether.

2. Eliud Kipchoge: Precision Carb Strategy

Kipchoge, the marathon world record holder, follows a meticulously controlled diet that incorporates carbs during taper week but avoids the overeating often associated with carb-loading. His focus is on balance and digestibility rather than sheer volume.

3. Mirinda Carfrae: Carb-Periodization Advocate

Ironman champion Mirinda Carfrae practices carb periodization, alternating low-carb and high-carb days during training to maximize glycogen use on race day without overloading.

Breaking the Carb-Loading Stereotype

For too long, carb-loading has been treated as an unquestionable pillar of endurance running. However, it’s not the only—or even the best—approach for every runner. A more nuanced view reveals that fueling strategies should be personalized based on:

• Race distance.
• Training adaptations.
• Digestive tolerance.
• Individual performance goals.

Conclusion: Carb-Loading Isn’t One-Size-Fits-All

Carb-loading remains a valuable tool for certain races and runners, but it’s not a universal requirement. Blindly following the tradition can lead to unnecessary weight gain, discomfort, or even diminished performance. Instead, runners should focus on understanding their own energy needs, experimenting with fueling strategies during training, and tailoring their pre-race nutrition to suit their goals.

So, is carb-loading essential? Sometimes—but not always. Run smart, fuel smarter, and let your body—not outdated advice—guide you to the finish line.

References

1. Sherman, W. M., et al. (1981). "Effect of Carbohydrate Loading on Performance." Journal of Applied Physiology.
2. Burke, L. M., et al. (2017). "Carbohydrates for training and competition." Journal of Sports Medicine.
3. Volek, J. S., et al. (2016). "Low-Carbohydrate Diets and Endurance Performance." Metabolism.

Additional Resources

Podcasts:

• The Science of Ultra: "The Truth About Carb-Loading."
• Fueling for the Long Run by Trail Runner Nation.

Videos:

• "How to Carb-Load Correctly" by The Running Channel (YouTube).
• "Do You Really Need to Carb-Load?" by Sage Canaday (YouTube).

Books:

• The Endurance Diet by Matt Fitzgerald: Insights into balanced fueling for endurance athletes.
• ROAR by Stacy Sims: A tailored approach to fueling for female athletes.