[maaaats]

> The metabolic efficiency of a human on a bicycle is remarkably good. Calorimetric studies have shown that a properly trained athlete will have efficiencies of 22 to 26% depending on pedal cadence and power output.

Anectdote about this, is that my watt meter on my bicycle gives out the total amount of work done in kJ at the end. To convert that to kcal in food, one can convert 1-to-1, as the metabolic efficiency matches roughly the ratio between kcal and kJ.