Picture this:
It’s the early 1900s, and a group of grueling cyclists are tearing through the French countryside, covering insane distances on rickety bikes. They don’t have energy gels, fancy nutrition bars, or scientific fueling plans. Instead, they survive by raiding the occasional village, grabbing whatever bread, cheese, or fruit they can find. Snack time was basically a high-speed scavenger hunt.
Fast forward over a hundred years, and everything has changed. Today’s riders consume up to 120 grams of carbohydrates per hour—not just to fill their stomachs, but as part of a precise endurance fueling strategy powered by cutting-edge sports nutrition science.
Why carbs and calories matter in the Tour de France
The Tour de France is no ordinary bike race. Covering roughly 3,400 kilometers over 21 days, riders burn between 5,000 and 9,000 calories every single day—about four times the energy needs of an average person. That’s like eating four full Thanksgiving dinners while pedaling uphill.
But how do we actually measure something so colossal and constantly changing?
Power meters: measuring energy burn precisely
Enter the power meter—a tiny gadget revolutionizing cycling. Unlike heart rate or pace, which estimate effort indirectly, the power meter measures mechanical power output directly, in watts. Think of it as a speedometer that doesn’t just tell you how fast you’re going, but exactly how hard you’re pushing the pedals at any moment.
This precise data allows coaches and scientists to calculate the exact amount of energy a rider is burning, measured in kilojoules (kJ).
Kilojoules vs. calories: understanding energy units
Now, you might wonder how kilojoules relate to calories—the energy units we see on nutrition labels.
One Calorie equals 4.184 kilojoules, but the human body isn’t 100% efficient at converting that energy into mechanical work. This efficiency, called Gross Metabolic Efficiency (GME), typically ranges from 20% to 25%.
In other words, when your body burns one Calorie (4.184 kJ), only about 20–25% of that energy is actually used for work; the rest is lost as heat.
Putting this into numbers:
1 Calorie × 25% = 0.25 → 0.25 × 4.184 kJ = roughly 1 kJ of mechanical work.
For practical purposes, cyclists approximate this as a 1:1 ratio between kilojoules of work and calories burned.
The carb absorption problem
For years, scientists thought the human gut could only absorb about 60 grams of carbohydrates per hour during exercise without causing stomach distress. That became the golden rule for endurance fueling.
But here’s the problem: 1 gram of carbohydrate holds 4 calories of energy.
Let’s break it down:
A pro rider averaging 250 watts for six hours—a typical mountainous stage—does 1,500 watt-hours of work, about 5,400 kilojoules.
That’s roughly 5,400 Calories, or about 900 Calories burned per hour.
If the rider ingests 60 grams of carbs per hour (240 Calories), they’re replacing just 27% of their hourly energy needs.
Today, most riders double that to 120 grams of carbs hourly—but even then, they only replace about 53% of their energy burn.
How do riders avoid bonking?
That means even high modern carb recommendations cover only about half the fuel tank. The rest comes from fat and stored glycogen—but those reserves are limited. When glycogen runs out, you hit “bonk city”—a total energy crash.
So, how do these athletes avoid hitting the wall every day?
The answer lies in meticulous nutrition planning before and after each stage. Teams have known the race routes for over six months and finalize their rider lineups about six weeks out. This lead time allows dietitians and chefs to craft precise meal plans to fill energy gaps and ensure the right foods are sourced and transported.
Smarter fueling with AI—and how you can fuel smarter too
Nowadays, this planning is getting even smarter thanks to AI. Advanced systems analyze rider biometric and power data, predict energy demands based on terrain and race conditions, and dynamically adjust fueling strategies on the fly.
No more guesswork. While teams plan ahead, nutrition has become a real-time, data-driven strategy perfectly synced to a rider’s body and race-day challenges—all the gaps covered at the breakfast table and after the stage to recover.
Fuel smarter, ride stronger, snack like a pro
But you don’t need a pro contract or fancy AI to snack smart.
Today, many fueling algorithms are right in your pocket, syncing with your own training data to deliver personalized snack math.
Even easier—try our Carb Calculator, built on the very science in this story, to fuel smarter, ride stronger, and snack like a pro.
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