Cycling at more than 16mph is deemed ‘racing’ by the Wisconsin Department of Health (2005). When cycling between 16-19mph, an average 75kg person is thought to burn approx 48kcal for every mile cycled.
The Tour de France covers 2100+ miles over the course of the 3 weeks, with each rider averaging between 25-30 mph! This equates to each athlete burning approx 126,000kcal over the 20 stages (not factoring the gruelling hill climbs)!
This comes out at approx 6300kcal a day...and that’s without considering the extra calories needed to accommodate the spike in resting basal metabolic after the race!!
Department of Health and Family Services, State of Wisconsin. Division of Public Health (2005). Calories Burned Per Hour. Retrieved 23rd March, 2012, from http://www.dhs.wisconsin.gov/health/physicalactivity/pdf_files/caloriesperhour.pdf