Here is a Calorie Burn Calculator for the cyclists to check how much fuel (calories) of their body exerts in the cycling activity. You have to burn 7716 calories to lose one kilogram of weight. The results are approximate.
"Your body's carbohydrate reserves amount to two or three thousand calories, and your fat reserves are more like 70,000 calories. For a typical rider, about 21% of your energy comes from fat, on average, and the rest from carbohydrates; with more carbohydrates being burned at higher levels of exertion. caffeine will increase the percentage of fat consumed for energy to 40% for the same exertion. When you run out of carbohydrates as an energy source, you "bonk" and have to slow right down unless you replace the energy as you use it." - BicycleSource.com