I actually know this because I did count Calories for some long strenuous hiking trips (the PCT, CDT, AT, etc.). And I push myself on bike tours in a similar fashion, averaging over 80 mpd, with lots of centuries. I always carry between 4000 and 5000 Calories per day, then supplement that when I can in town, with pints of Ben & Jerry's, orders of fries, fresh fruit and veg (preferred diet is plant-based). Some days exceed 6000, some are as low as 4000.
I maintain body weight and muscle mass, with decent nutrition, and stay healthy on long (five to six month) trips. On a couple of the hiking trips, I took a leave of absence from a job as a firefighter, and returned to work without noticeable loss of upper body muscle.