As I said you have to make an assumption about your metabolic efficiency in turning your food/stored energy into mechanical work. There are about 4.2 kJ in a kcal (food calorie), so if we were 100% efficient, we would only need to eat about .24 calories for every kJ our power meter shows us. But we are not that efficient. Testing has shown that most people are between 18 to 24% efficient. So if you assume 24% efficiency, then 1kJ would be 1kcal, but if you took the other end of that, you are looking at a factor around 1.15, and that's a big difference.
understood and thank you for going into such detail...
i am doing this cycling study for a new powerade drink and they are giving me the whole max power, vo2, etc tests next week (
cycling study ) and believe that they will be doing efficiency tests over the next five weeks to measure the usage of the product (they specifically said that they would be measuring intake and exit of gases, so i think they will be doing what you referred to earlier. this would really benefit me and give me honest to goodness numbers to work off of for diet control.