Originally Posted by
rubiksoval
Rule of thumb is 1 kJ = 1 calorie. 276 average watts = 1 mJ an hour.
1 mJ an hour = 1,000 calories.
Zero reason to make it any more complicated than that. 6 calories = 1.5 grams of sugar. Not consequential in the least.
For completeness, it is not mJ, but MJ what you mean. Small m is used for milli and capital M is used for mega. And it is not calories but k calories, also written as kcal.
But yes, in general you can say that 1kJ of work amounts to 1 kcal of food. (for people that plug these numbers in some type of online converter and get different figures, you also have to consider that there is an additional factor of 4 to account for efficiency of body, i.e. you need to eat 4 times more energie than the energie that was needed to move the bike)
I normally think of it in terms of average power and multiply by 3.5 to get to kcal per hour, as I find it easier when I envision a certain ride to estimate average power than it is to estimate total kJ.