Who Really Needs Carbs? Not 95% of You.

Introduction

For decades, runners have been told to slam carbs to survive long races. Gels, sports drinks, carb-loading dinners—these are treated like gospel in endurance culture. But here’s the honest truth:

Unless you're an elite athlete pushing near your physiological limit, you don’t need to flood your system with sugar to finish strong.

In fact, most runners—yes, the overwhelming majority—could improve performance, reduce gut issues, and avoid mid-race crashes by fueling smarter. That means rethinking the overreliance on carbohydrates.

This article is for the 95% of runners who aren’t racing at sub-2:30 marathon pace. We’ll break down how the body really produces energy, what different intensity levels demand, and how fat—your most powerful fuel—can do more than you think.

Ready to run smarter, not just sugar-harder? Let’s get into it.

Metabolic Pathways 101: How Your Body Actually Produces Energy

Your body has multiple energy systems. Most discussions around marathon fueling fixate on carbs—but that’s only part of the picture. Let’s get clinical for a second.

Carbohydrate Oxidation

• Fast source of ATP (your cellular energy currency).

• Relies on blood glucose and stored muscle/liver glycogen.

• Glycogen storage is limited: ~400–500g total.

• Dominates at very high intensities (>70% VO₂ max).
  👉 Great for short bursts or elite-level pace. Not built for the long haul at submaximal effort.

Fat Oxidation

• Traditionally seen as “slow,” but in trained athletes, that’s outdated thinking.

• Trained endurance runners oxidize ~0.8 g/min.

• Fat-adapted athletes can reach up to 1.5 g/min.

• Even lean athletes carry >50,000 kcal of fat.

• Best utilized at ≤70% VO₂ max.
  👉 Steady, powerful, nearly unlimited fuel source. Ideal for marathon and ultramarathon efforts.

Lactate Utilization

• Often misunderstood as "waste." It's not.

• Lactate is a byproduct of glycolysis (carb metabolism), but your body recycles it—fast.

• Used efficiently by the heart, brain, and muscles, especially near the lactate threshold.
  👉 A flexible, high-performance fuel source when managed correctly.

Real-World Example: 3-Hour Marathoner Fueling at a 50/50 Carb-Fat Split

Let’s crunch the numbers.

Athlete:

• 70 kg male

• 3-hour marathon

• Fuel split: 50% carbs / 50% fats

Total Energy Demand:

• 42.195 km x 70 kcal/km = ~2954 kcal

From Carbohydrates:

• 1477 kcal / 4 = ~369 g of carbs

• That’s ~123 g/hour

From Fat:

• 1477 kcal / 9 = ~164 g of fat

• That’s ~55 g/hour

Key Insight:

• The gut can only absorb ~90–120 g of carbs per hour (best-case scenario).

• Anything beyond that depends on internal glycogen and fat oxidation.

• With fat oxidation rates at 0.8–1.5 g/min, trained athletes can easily cover up to half their energy needs from fat.

👉 You don’t need to overload carbs to perform. You need to fuel according to how your body actually works.

Marathon and Ultramarathon Energy Realities

Let’s kill the myth: Only about 5% of marathoners run above 70% VO₂ max, where carbs become mandatory. That means:

95% of runners are operating in a zone where fat should be doing the heavy lifting.

Still carb-loading like a Tour de France cyclist? You’re not just wasting effort—you’re probably wrecking your gut and risking a crash.

How Much Carbohydrate Do You Actually Need?

Let’s go back to our 3-hour marathoner:

• At a 50/50 fuel split, 10–30 g of carbs per hour is enough to stabilize blood glucose.

• Glycogen + fat oxidation do the rest.

So who needs 60+ g/hour?

Only a tiny elite segment of runners performing at consistently high intensities (>70% VO₂ max). For the rest, that level of carb intake isn’t just unnecessary—it’s counterproductive.

Ultramarathons: The Fat-Fueled Frontier

Run 6+ hours and things shift even further. Welcome to ultramarathons, where fat reigns.

• The longer the race, the lower the intensity.

• Lower intensity = more fat utilization.

• At this point, 10–30 g of carbs/hour is plenty to keep blood sugar stable.

• The real threat isn’t underfueling—it’s gut destruction.

Reality Check:

• Carb intake recommendations have climbed for years.

• But GI distress remains the #1 cause of DNFs in ultras.

👉 More sugar doesn't equal more success. Protect your gut. Prioritize metabolic flexibility. Trust your fat adaptation.

Summary Table: Who Actually Needs Carbs?

Fuel Reality Check: Stop Copying the Elites.

The Honest Question: Which One Are You?

Most runners blindly copy elite strategies, but here’s the hard truth:

You’re not Kipchoge. You’re not racing at 90% VO₂ max. And your gut knows it.

If you're a real-world runner—juggling work, stress, and life—your best performance won't come from mimicking elite carb loading. It will come from:

• Trusting your fat metabolism

• Fueling according to your pace and physiology

• Minimizing gut disruption

• Avoiding sugar spikes and crashes

Conclusion: Ditch the Sugar Spiral. Fuel Like You Mean It.

You don’t need to be a keto zealot. But you do need to stop fueling like a candy machine.

• Fat is not the enemy—it’s your backup generator and your main engine.

• Carbs are a tool—not the foundation.

• Gut health is performance. Period.

Fuel Intelligently. Run Relentlessly. Be the One Who Finishes.