Carbohydrates: who really needs them? Not the vast majority of athletes.

Introduction

For decades, runners have been told that they need to load up on carbohydrates to survive long distances.
Gels, isotonic drinks, carb-loading meals: all of this has become a kind of dogma in endurance culture.

But here is the truth, without mincing words:

Unless you are an elite athlete running close to your physiological limits, you don't need to flood your body with sugar to finish a race well.

In reality, the majority of runners — yes, the overwhelming majority — could improve their performance, reduce digestive problems and avoid fatigue by eating more intelligently.
This implies rethinking excessive dependence on carbohydrates .

This article is for the 95% of runners who do not run a marathon in less than 2 hours 30 minutes.
We'll look at how the body actually produces energy, what different intensity levels require, and why lipids — your most powerful fuel — are widely underestimated .

Ready to run smarter, not just sweeter?
Let's get down to business.

---

Metabolic pathways: how your body actually produces energy

The human body has several energy systems.
Most discussions about marathon fueling focus solely on carbohydrates — but that's only part of the equation.

Let's take a slightly more scientific approach.

---

Carbohydrate oxidation

– A rapid source of ATP (the energy currency of cells)
– Depends on blood glucose and glycogen stored in the muscles and liver
– Glycogen reserves are limited: approximately 400 to 500 g in total
– Becomes dominant at very high intensity ( > 70% of VO₂ max )

👉 Perfect for short efforts or elite paces.
👉 Not designed to last long periods at sub-maximal intensity.

---

Lipid oxidation

Long considered "slow", this view is now outdated among trained athletes.

– A trained endurance runner oxidizes approximately 0.8 g of lipids per minute
– A fat-adapted athlete can reach 1.5 g/min
– Even a very lean athlete carries more than 50,000 kcal in the form of fat
– Primarily used at ≤ 70% of VO₂ max

👉 A stable, powerful and virtually unlimited energy source.
👉 Ideal for marathons and ultra-endurance events.

---

Use of lactate

Often misunderstood, lactate is not a waste product .

It is a by-product of carbohydrate metabolism, which the body recycles very efficiently.
The heart, brain, and muscles use it as fuel, particularly around the lactate threshold.

👉 A flexible and efficient fuel, when properly managed.

---

Concrete example: a marathon in 3 hours with a 50% carbohydrate / 50% fat distribution

Let's do the calculations.

Athlete :
– Male, 70 kg
– Marathon in 3 hours
– Energy breakdown: 50% carbohydrates / 50% lipids

Total energy expenditure:
42.195 km × 70 kcal/km ≈ 2954 kcal

Contribution via carbohydrates:
1477 kcal ÷ 4 = ≈ 369 g of carbohydrates
➡️ ≈ 123 g/hour

Contribution via lipids:
1477 kcal ÷ 9 = ≈ 164 g of lipids
➡️ ≈ 55 g/hour

Key point

The intestine can absorb approximately 90 to 120 g of carbohydrates per hour , in the best of circumstances.
Beyond that, the organization must rely on:
– internal glycogen
– lipid oxidation

With fat oxidation between 0.8 and 1.5 g/min , a trained athlete can cover up to half of their energy needs with lipids .

👉 It is not necessary to overload on carbohydrates to perform.
👉 You need to eat according to the body's actual function.

---

Marathon and ultra: the energy reality

Let's debunk a myth: only about 5% of marathon runners run above 70% of VO₂ max , where carbohydrates become essential.

This means that 95% of runners operate in a zone where lipids should be doing most of the work .

Continuing to carb-load like a Tour de France cyclist is not only pointless:
This is often the best way to ruin your digestive system and cause a crash.

---

How many carbohydrates do you actually need?

Let's get back to our marathon runner in 3 hours.

With a 50/50 split:
– 10 to 30 g of carbohydrates per hour is sufficient to stabilize blood sugar
– glycogen and lipids do the rest

So, who actually needs 60 g/h or more ?

👉 A tiny minority of elite athletes run at high intensity continuously.
For everyone else, this level of input is unnecessary — or even counterproductive .

---

Ultra-trail running: the natural territory of lipids

Beyond 6 hours of effort , the logic changes even more.

– The longer the race, the lower the intensity
– The lower the intensity, the greater the use of lipids

In this context, 10 to 30 g of carbohydrates per hour is more than enough to maintain stable blood sugar levels.

The real danger is not a lack of energy.
👉 This is the destruction of the digestive system.

On-the-ground reality

Carbohydrate recommendations have been steadily increasing.
However, gastrointestinal disorders remain the leading cause of withdrawal in ultramarathons.

👉 More sugar ≠ more success.
👉 Protecting your gut, developing your metabolic flexibility and trusting lipids is often the key.

---

Summary table: who really needs carbohydrates?

Stop copying the elites.

The real question is: which category are you in?

---

Eat smart.
Course with consistency.
Be the one who finishes.